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The rt_mutex structure's ->owner field is read locklessly, so this
commit adds the WRITE_ONCE() to an update in order to provide proper
documentation and READ_ONCE()/WRITE_ONCE() pairing.
This data race was reported by KCSAN. Not appropriate for backporting
due to failure being unlikely.
Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Will Deacon <[email protected]>
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We are missing this annotation in percpu_down_write(). Correct
this.
Signed-off-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Waiman Long <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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Now that __percpu_up_read() is only ever used from percpu_up_read()
merge them, it's a small function.
Signed-off-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Waiman Long <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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Remove the now unused RWSEM_OWNER_UNKNOWN hack. This hack breaks
PREEMPT_RT and getting rid of it was the entire motivation for
re-writing the percpu rwsem.
The biggest problem is that it is fundamentally incompatible with any
form of Priority Inheritance, any exclusively held lock must have a
distinct owner.
Requested-by: Christoph Hellwig <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Waiman Long <[email protected]>
Tested-by: Juri Lelli <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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The filesystem freezer uses percpu-rwsem in a way that is effectively
write_non_owner() and achieves this with a few horrible hacks that
rely on the rwsem (!percpu) implementation.
When PREEMPT_RT replaces the rwsem implementation with a PI aware
variant this comes apart.
Remove the embedded rwsem and implement it using a waitqueue and an
atomic_t.
- make readers_block an atomic, and use it, with the waitqueue
for a blocking test-and-set write-side.
- have the read-side wait for the 'lock' state to clear.
Have the waiters use FIFO queueing and mark them (reader/writer) with
a new WQ_FLAG. Use a custom wake_function to wake either a single
writer or all readers until a writer.
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Waiman Long <[email protected]>
Tested-by: Juri Lelli <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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In preparation for removing the embedded rwsem and building a custom
lock, extract the read-trylock primitive.
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Waiman Long <[email protected]>
Tested-by: Juri Lelli <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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As preparation to rework __percpu_down_read() move the
__this_cpu_inc() into it.
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Waiman Long <[email protected]>
Tested-by: Juri Lelli <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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Use bool where possible.
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Waiman Long <[email protected]>
Tested-by: Juri Lelli <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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As preparation for replacing the embedded rwsem, give percpu-rwsem its
own lockdep_map.
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Waiman Long <[email protected]>
Tested-by: Juri Lelli <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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Once a lock class is zapped, all the lock chains that include the zapped
class are essentially useless. The lock_chain structure itself can be
reused, but not the corresponding chain_hlocks[] entries. Over time,
we will run out of chain_hlocks entries while there are still plenty
of other lockdep array entries available.
To fix this imbalance, we have to make chain_hlocks entries reusable
just like the others. As the freed chain_hlocks entries are in blocks of
various lengths. A simple bitmap like the one used in the other reusable
lockdep arrays isn't applicable. Instead the chain_hlocks entries are
put into bucketed lists (MAX_CHAIN_BUCKETS) of chain blocks. Bucket 0
is the variable size bucket which houses chain blocks of size larger than
MAX_CHAIN_BUCKETS sorted in decreasing size order. Initially, the whole
array is in one chain block (the primordial chain block) in bucket 0.
The minimum size of a chain block is 2 chain_hlocks entries. That will
be the minimum allocation size. In other word, allocation requests
for one chain_hlocks entry will cause 2-entry block to be returned and
hence 1 entry will be wasted.
Allocation requests for the chain_hlocks are fulfilled first by looking
for chain block of matching size. If not found, the first chain block
from bucket[0] (the largest one) is split. That can cause hlock entries
fragmentation and reduce allocation efficiency if a chain block of size >
MAX_CHAIN_BUCKETS is ever zapped and put back to after the primordial
chain block. So the MAX_CHAIN_BUCKETS must be large enough that this
should seldom happen.
By reusing the chain_hlocks entries, we are able to handle workloads
that add and zap a lot of lock classes without the risk of running out
of chain_hlocks entries as long as the total number of outstanding lock
classes at any time remain within a reasonable limit.
Two new tracking counters, nr_free_chain_hlocks & nr_large_chain_blocks,
are added to track the total number of chain_hlocks entries in the
free bucketed lists and the number of large chain blocks in buckets[0]
respectively. The nr_free_chain_hlocks replaces nr_chain_hlocks.
The nr_large_chain_blocks counter enables to see if we should increase
the number of buckets (MAX_CHAIN_BUCKETS) available so as to avoid to
avoid the fragmentation problem in bucket[0].
An internal nfsd test that ran for more than an hour and kept on
loading and unloading kernel modules could cause the following message
to be displayed.
[ 4318.443670] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
The patched kernel was able to complete the test with a lot of free
chain_hlocks entries to spare:
# cat /proc/lockdep_stats
:
dependency chains: 18867 [max: 65536]
dependency chain hlocks: 74926 [max: 327680]
dependency chain hlocks lost: 0
:
zapped classes: 1541
zapped lock chains: 56765
large chain blocks: 1
By changing MAX_CHAIN_BUCKETS to 3 and add a counter for the size of the
largest chain block. The system still worked and We got the following
lockdep_stats data:
dependency chains: 18601 [max: 65536]
dependency chain hlocks used: 73133 [max: 327680]
dependency chain hlocks lost: 0
:
zapped classes: 1541
zapped lock chains: 56702
large chain blocks: 45165
large chain block size: 20165
By running the test again, I was indeed able to cause chain_hlocks
entries to get lost:
dependency chain hlocks used: 74806 [max: 327680]
dependency chain hlocks lost: 575
:
large chain blocks: 48737
large chain block size: 7
Due to the fragmentation, it is possible that the
"MAX_LOCKDEP_CHAIN_HLOCKS too low!" error can happen even if a lot of
of chain_hlocks entries appear to be free.
Fortunately, a MAX_CHAIN_BUCKETS value of 16 should be big enough that
few variable sized chain blocks, other than the initial one, should
ever be present in bucket 0.
Suggested-by: Peter Zijlstra <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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Add a new counter nr_zapped_lock_chains to track the number lock chains
that have been removed.
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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If a lock chain contains a class that is zapped, the whole lock chain is
likely to be invalid. If the zapped class is at the end of the chain,
the partial chain without the zapped class should have been stored
already as the current code will store all its predecessor chains. If
the zapped class is somewhere in the middle, there is no guarantee that
the partial chain will actually happen. It may just clutter up the hash
and make searching slower. I would rather prefer storing the chain only
when it actually happens.
So just dump the corresponding chain_hlocks entries for now. A latter
patch will try to reuse the freed chain_hlocks entries.
This patch also changes the type of nr_chain_hlocks to unsigned integer
to be consistent with the other counters.
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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The whole point of the lockdep dynamic key patch is to allow unused
locks to be removed from the lockdep data buffers so that existing
buffer space can be reused. However, there is no way to find out how
many unused locks are zapped and so we don't know if the zapping process
is working properly.
Add a new nr_zapped_classes counter to track that and show it in
/proc/lockdep_stats.
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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Currently, the irq_context field of a lock chains displayed in
/proc/lockdep_chains is just a number. It is likely that many people
may not know what a non-zero number means. To make the information more
useful, print the actual irq names ("softirq" and "hardirq") instead.
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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There are currently three counters to track the IRQ context of a lock
chain - nr_hardirq_chains, nr_softirq_chains and nr_process_chains.
They are incremented when a new lock chain is added, but they are
not decremented when a lock chain is removed. That causes some of the
statistic counts reported by /proc/lockdep_stats to be incorrect.
IRQ
Fix that by decrementing the right counter when a lock chain is removed.
Since inc_chains() no longer accesses hardirq_context and softirq_context
directly, it is moved out from the CONFIG_TRACE_IRQFLAGS conditional
compilation block.
Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer in use")
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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The most notable change is DEFINE_SHOW_ATTRIBUTE macro split in
seq_file.h.
Conversion rule is:
llseek => proc_lseek
unlocked_ioctl => proc_ioctl
xxx => proc_xxx
delete ".owner = THIS_MODULE" line
[[email protected]: fix drivers/isdn/capi/kcapi_proc.c]
[[email protected]: fix kernel/sched/psi.c]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/20191225172546.GB13378@avx2
Signed-off-by: Alexey Dobriyan <[email protected]>
Signed-off-by: Stephen Rothwell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
"Just a handful of changes in this cycle: an ARM64 performance
optimization, a comment fix and a debug output fix"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
locking/osq: Use optimized spinning loop for arm64
locking/qspinlock: Fix inaccessible URL of MCS lock paper
locking/lockdep: Fix lockdep_stats indentation problem
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Arm64 has a more optimized spinning loop (atomic_cond_read_acquire)
using wfe for spinlock that can boost performance of sibling threads
by putting the current cpu to a wait state that is broken only when
the monitored variable changes or an external event happens.
OSQ has a more complicated spinning loop. Besides the lock value, it
also checks for need_resched() and vcpu_is_preempted(). The check for
need_resched() is not a problem as it is only set by the tick interrupt
handler. That will be detected by the spinning cpu right after iret.
The vcpu_is_preempted() check, however, is a problem as changes to the
preempt state of of previous node will not affect the wait state. For
ARM64, vcpu_is_preempted is not currently defined and so is a no-op.
Will has indicated that he is planning to para-virtualize wfe instead
of defining vcpu_is_preempted for PV support. So just add a comment in
arch/arm64/include/asm/spinlock.h to indicate that vcpu_is_preempted()
should not be defined as suggested.
On a 2-socket 56-core 224-thread ARM64 system, a kernel mutex locking
microbenchmark was run for 10s with and without the patch. The
performance numbers before patch were:
Running locktest with mutex [runtime = 10s, load = 1]
Threads = 224, Min/Mean/Max = 316/123,143/2,121,269
Threads = 224, Total Rate = 2,757 kop/s; Percpu Rate = 12 kop/s
After patch, the numbers were:
Running locktest with mutex [runtime = 10s, load = 1]
Threads = 224, Min/Mean/Max = 334/147,836/1,304,787
Threads = 224, Total Rate = 3,311 kop/s; Percpu Rate = 15 kop/s
So there was about 20% performance improvement.
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Will Deacon <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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It turns out that the URL of the MCS lock paper listed in the source
code is no longer accessible. I did got question about where the paper
was. This patch updates the URL to BZ 206115 which contains a copy of
the paper from
https://www.cs.rochester.edu/u/scott/papers/1991_TOCS_synch.pdf
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Will Deacon <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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It was found that two lines in the output of /proc/lockdep_stats have
indentation problem:
# cat /proc/lockdep_stats
:
in-process chains: 25057
stack-trace entries: 137827 [max: 524288]
number of stack traces: 7973
number of stack hash chains: 6355
combined max dependencies: 1356414598
hardirq-safe locks: 57
hardirq-unsafe locks: 1286
:
All the numbers displayed in /proc/lockdep_stats except the two stack
trace numbers are formatted with a field with of 11. To properly align
all the numbers, a field width of 11 is now added to the two stack
trace numbers.
Fixes: 8c779229d0f4 ("locking/lockdep: Report more stack trace statistics")
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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The commit 91d2a812dfb9 ("locking/rwsem: Make handoff writer
optimistically spin on owner") will allow a recently woken up waiting
writer to spin on the owner. Unfortunately, if the owner happens to be
RWSEM_OWNER_UNKNOWN, the code will incorrectly spin on it leading to a
kernel crash. This is fixed by passing the proper non-spinnable bits
to rwsem_spin_on_owner() so that RWSEM_OWNER_UNKNOWN will be treated
as a non-spinnable target.
Fixes: 91d2a812dfb9 ("locking/rwsem: Make handoff writer optimistically spin on owner")
Reported-by: Christoph Hellwig <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Christoph Hellwig <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
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If the lockdep code is really running out of the stack_trace entries,
it is likely that buffer overrun can happen and the data immediately
after stack_trace[] will be corrupted.
If there is less than LOCK_TRACE_SIZE_IN_LONGS entries left before
the call to save_trace(), the max_entries computation will leave it
with a very large positive number because of its unsigned nature. The
subsequent call to stack_trace_save() will then corrupt the data after
stack_trace[]. Fix that by changing max_entries to a signed integer
and check for negative value before calling stack_trace_save().
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: 12593b7467f9 ("locking/lockdep: Reduce space occupied by stack traces")
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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This ended up causing some noise in places such as rxrpc running in softirq.
The warning is misleading in this case as the mutex trylock and unlock
operations are done within the same context; and therefore we need not
worry about the PI-boosting issues that comes along with no single-owner
lock guarantees.
While we don't want to support this in mutexes, there is no way out of
this yet; so lets get rid of the WARNs for now, as it is only fair to
code that has historically relied on non-preemptible softirq guarantees.
In addition, changing the lock type is also unviable: exclusive rwsems
have the same issue (just not the WARN_ON) and counting semaphores
would introduce a performance hit as mutexes are a lot more optimized.
This reverts:
a0855d24fc22: ("locking/mutex: Complain upon mutex API misuse in IRQ contexts")
Fixes: a0855d24fc22: ("locking/mutex: Complain upon mutex API misuse in IRQ contexts")
Signed-off-by: Davidlohr Bueso <[email protected]>
Tested-by: David Howells <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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This fixes various data races in spinlock_debug. By testing with KCSAN,
it is observable that the console gets spammed with data races reports,
suggesting these are extremely frequent.
Example data race report:
read to 0xffff8ab24f403c48 of 4 bytes by task 221 on cpu 2:
debug_spin_lock_before kernel/locking/spinlock_debug.c:85 [inline]
do_raw_spin_lock+0x9b/0x210 kernel/locking/spinlock_debug.c:112
__raw_spin_lock include/linux/spinlock_api_smp.h:143 [inline]
_raw_spin_lock+0x39/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
get_partial_node.isra.0.part.0+0x32/0x2f0 mm/slub.c:1873
get_partial_node mm/slub.c:1870 [inline]
<snip>
write to 0xffff8ab24f403c48 of 4 bytes by task 167 on cpu 3:
debug_spin_unlock kernel/locking/spinlock_debug.c:103 [inline]
do_raw_spin_unlock+0xc9/0x1a0 kernel/locking/spinlock_debug.c:138
__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:159 [inline]
_raw_spin_unlock_irqrestore+0x2d/0x50 kernel/locking/spinlock.c:191
spin_unlock_irqrestore include/linux/spinlock.h:393 [inline]
free_debug_processing+0x1b3/0x210 mm/slub.c:1214
__slab_free+0x292/0x400 mm/slub.c:2864
<snip>
As a side-effect, with KCSAN, this eventually locks up the console, most
likely due to deadlock, e.g. .. -> printk lock -> spinlock_debug ->
KCSAN detects data race -> kcsan_print_report() -> printk lock ->
deadlock.
This fix will 1) avoid the data races, and 2) allow using lock debugging
together with KCSAN.
Reported-by: Qian Cai <[email protected]>
Signed-off-by: Marco Elver <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
"The main changes in this cycle were:
- A comprehensive rewrite of the robust/PI futex code's exit handling
to fix various exit races. (Thomas Gleixner et al)
- Rework the generic REFCOUNT_FULL implementation using
atomic_fetch_* operations so that the performance impact of the
cmpxchg() loops is mitigated for common refcount operations.
With these performance improvements the generic implementation of
refcount_t should be good enough for everybody - and this got
confirmed by performance testing, so remove ARCH_HAS_REFCOUNT and
REFCOUNT_FULL entirely, leaving the generic implementation enabled
unconditionally. (Will Deacon)
- Other misc changes, fixes, cleanups"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (27 commits)
lkdtm: Remove references to CONFIG_REFCOUNT_FULL
locking/refcount: Remove unused 'refcount_error_report()' function
locking/refcount: Consolidate implementations of refcount_t
locking/refcount: Consolidate REFCOUNT_{MAX,SATURATED} definitions
locking/refcount: Move saturation warnings out of line
locking/refcount: Improve performance of generic REFCOUNT_FULL code
locking/refcount: Move the bulk of the REFCOUNT_FULL implementation into the <linux/refcount.h> header
locking/refcount: Remove unused refcount_*_checked() variants
locking/refcount: Ensure integer operands are treated as signed
locking/refcount: Define constants for saturation and max refcount values
futex: Prevent exit livelock
futex: Provide distinct return value when owner is exiting
futex: Add mutex around futex exit
futex: Provide state handling for exec() as well
futex: Sanitize exit state handling
futex: Mark the begin of futex exit explicitly
futex: Set task::futex_state to DEAD right after handling futex exit
futex: Split futex_mm_release() for exit/exec
exit/exec: Seperate mm_release()
futex: Replace PF_EXITPIDONE with a state
...
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This changes "to the list" to "from the list" and also deletes the
obsolete comment about the "@nested" argument.
The "nested" argument was removed in this commit, earlier this year:
5facae4f3549 ("locking/lockdep: Remove unused @nested argument from lock_release()").
Signed-off-by: Dan Carpenter <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Will Deacon <[email protected]>
Link: https://lkml.kernel.org/r/20191104091252.GA31509@mwanda
Signed-off-by: Ingo Molnar <[email protected]>
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Add warning checks if mutex_trylock() or mutex_unlock() are used in
IRQ contexts, under CONFIG_DEBUG_MUTEXES=y.
While the mutex rules and semantics are explicitly documented, this allows
to expose any abusers and robustifies the whole thing.
While trylock and unlock are non-blocking, calling from IRQ context
is still forbidden (lock must be within the same context as unlock).
Signed-off-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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Since the following commit:
b4adfe8e05f1 ("locking/lockdep: Remove unused argument in __lock_release")
@nested is no longer used in lock_release(), so remove it from all
lock_release() calls and friends.
Signed-off-by: Qian Cai <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Daniel Vetter <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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Including rwlock.h directly will cause kernel builds to fail
if CONFIG_PREEMPT_RT is defined. The correct header file
(rwlock_rt.h OR rwlock.h) will be included by spinlock.h which
is included by locktorture.c anyway.
Remove the include of linux/rwlock.h.
Signed-off-by: Wolfgang M. Reimer <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Acked-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
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The strncmp() function is error-prone because it is easy to get the
length wrong, especially if the string is subject to change, especially
given the need to account for the terminating nul byte. This commit
therefore substitutes the newly introduced str_has_prefix(), which
does not require a separately specified length.
Signed-off-by: Chuhong Yuan <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
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This patch reverts commit 75437bb304b20 (locking/pvqspinlock: Don't
wait if vCPU is preempted). A large performance regression was caused
by this commit. on over-subscription scenarios.
The test was run on a Xeon Skylake box, 2 sockets, 40 cores, 80 threads,
with three VMs of 80 vCPUs each. The score of ebizzy -M is reduced from
13000-14000 records/s to 1700-1800 records/s:
Host Guest score
vanilla w/o kvm optimizations upstream 1700-1800 records/s
vanilla w/o kvm optimizations revert 13000-14000 records/s
vanilla w/ kvm optimizations upstream 4500-5000 records/s
vanilla w/ kvm optimizations revert 14000-15500 records/s
Exit from aggressive wait-early mechanism can result in premature yield
and extra scheduling latency.
Actually, only 6% of wait_early events are caused by vcpu_is_preempted()
being true. However, when one vCPU voluntarily releases its vCPU, all
the subsequently waiters in the queue will do the same and the cascading
effect leads to bad performance.
kvm optimizations:
[1] commit d73eb57b80b (KVM: Boost vCPUs that are delivering interrupts)
[2] commit 266e85a5ec9 (KVM: X86: Boost queue head vCPU to mitigate lock waiter preemption)
Tested-by: [email protected]
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: [email protected]
Cc: [email protected]
Fixes: 75437bb304b20 (locking/pvqspinlock: Don't wait if vCPU is preempted)
Signed-off-by: Wanpeng Li <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler updates from Ingo Molnar:
- MAINTAINERS: Add Mark Rutland as perf submaintainer, Juri Lelli and
Vincent Guittot as scheduler submaintainers. Add Dietmar Eggemann,
Steven Rostedt, Ben Segall and Mel Gorman as scheduler reviewers.
As perf and the scheduler is getting bigger and more complex,
document the status quo of current responsibilities and interests,
and spread the review pain^H^H^H^H fun via an increase in the Cc:
linecount generated by scripts/get_maintainer.pl. :-)
- Add another series of patches that brings the -rt (PREEMPT_RT) tree
closer to mainline: split the monolithic CONFIG_PREEMPT dependencies
into a new CONFIG_PREEMPTION category that will allow the eventual
introduction of CONFIG_PREEMPT_RT. Still a few more hundred patches
to go though.
- Extend the CPU cgroup controller with uclamp.min and uclamp.max to
allow the finer shaping of CPU bandwidth usage.
- Micro-optimize energy-aware wake-ups from O(CPUS^2) to O(CPUS).
- Improve the behavior of high CPU count, high thread count
applications running under cpu.cfs_quota_us constraints.
- Improve balancing with SCHED_IDLE (SCHED_BATCH) tasks present.
- Improve CPU isolation housekeeping CPU allocation NUMA locality.
- Fix deadline scheduler bandwidth calculations and logic when cpusets
rebuilds the topology, or when it gets deadline-throttled while it's
being offlined.
- Convert the cpuset_mutex to percpu_rwsem, to allow it to be used from
setscheduler() system calls without creating global serialization.
Add new synchronization between cpuset topology-changing events and
the deadline acceptance tests in setscheduler(), which were broken
before.
- Rework the active_mm state machine to be less confusing and more
optimal.
- Rework (simplify) the pick_next_task() slowpath.
- Improve load-balancing on AMD EPYC systems.
- ... and misc cleanups, smaller fixes and improvements - please see
the Git log for more details.
* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (53 commits)
sched/psi: Correct overly pessimistic size calculation
sched/fair: Speed-up energy-aware wake-ups
sched/uclamp: Always use 'enum uclamp_id' for clamp_id values
sched/uclamp: Update CPU's refcount on TG's clamp changes
sched/uclamp: Use TG's clamps to restrict TASK's clamps
sched/uclamp: Propagate system defaults to the root group
sched/uclamp: Propagate parent clamps
sched/uclamp: Extend CPU's cgroup controller
sched/topology: Improve load balancing on AMD EPYC systems
arch, ia64: Make NUMA select SMP
sched, perf: MAINTAINERS update, add submaintainers and reviewers
sched/fair: Use rq_lock/unlock in online_fair_sched_group
cpufreq: schedutil: fix equation in comment
sched: Rework pick_next_task() slow-path
sched: Allow put_prev_task() to drop rq->lock
sched/fair: Expose newidle_balance()
sched: Add task_struct pointer to sched_class::set_curr_task
sched: Rework CPU hotplug task selection
sched/{rt,deadline}: Fix set_next_task vs pick_next_task
sched: Fix kerneldoc comment for ia64_set_curr_task
...
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
- improve rwsem scalability
- add uninitialized rwsem debugging check
- reduce lockdep's stacktrace memory usage and add diagnostics
- misc cleanups, code consolidation and constification
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
mutex: Fix up mutex_waiter usage
locking/mutex: Use mutex flags macro instead of hard code
locking/mutex: Make __mutex_owner static to mutex.c
locking/qspinlock,x86: Clarify virt_spin_lock_key
locking/rwsem: Check for operations on an uninitialized rwsem
locking/rwsem: Make handoff writer optimistically spin on owner
locking/lockdep: Report more stack trace statistics
locking/lockdep: Reduce space occupied by stack traces
stacktrace: Constify 'entries' arguments
locking/lockdep: Make it clear that what lock_class::key points at is not modified
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Pick up the first couple of patches working towards PREEMPT_RT.
Signed-off-by: Ingo Molnar <[email protected]>
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The patch moving bits into mutex.c was a little too much; by also
moving struct mutex_waiter a few less common CONFIGs would no longer
build.
Fixes: 5f35d5a66b3e ("locking/mutex: Make __mutex_owner static to mutex.c")
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
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Use the mutex flag macro instead of hard code value inside
__mutex_owner().
Signed-off-by: Mukesh Ojha <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
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__mutex_owner() should only be used by the mutex api's.
So, to put this restiction let's move the __mutex_owner()
function definition from linux/mutex.h to mutex.c file.
There exist functions that uses __mutex_owner() like
mutex_is_locked() and mutex_trylock_recursive(), So
to keep legacy thing intact move them as well and
export them.
Move mutex_waiter structure also to keep it private to the
file.
Signed-off-by: Mukesh Ojha <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
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Currently rwsems is the only locking primitive that lacks this
debug feature. Add it under CONFIG_DEBUG_RWSEMS and do the magic
checking in the locking fastpath (trylock) operation such that
we cover all cases. The unlocking part is pretty straightforward.
Signed-off-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Waiman Long <[email protected]>
Cc: [email protected]
Cc: Davidlohr Bueso <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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When the handoff bit is set by a writer, no other tasks other than
the setting writer itself is allowed to acquire the lock. If the
to-be-handoff'ed writer goes to sleep, there will be a wakeup latency
period where the lock is free, but no one can acquire it. That is less
than ideal.
To reduce that latency, the handoff writer will now optimistically spin
on the owner if it happens to be a on-cpu writer. It will spin until
it releases the lock and the to-be-handoff'ed writer can then acquire
the lock immediately without any delay. Of course, if the owner is not
a on-cpu writer, the to-be-handoff'ed writer will have to sleep anyway.
The optimistic spinning code is also modified to not stop spinning
when the handoff bit is set. This will prevent an occasional setting of
handoff bit from causing a bunch of optimistic spinners from entering
into the wait queue causing significant reduction in throughput.
On a 1-socket 22-core 44-thread Skylake system, the AIM7 shared_memory
workload was run with 7000 users. The throughput (jobs/min) of the
following kernels were as follows:
1) 5.2-rc6
- 8,092,486
2) 5.2-rc6 + tip's rwsem patches
- 7,567,568
3) 5.2-rc6 + tip's rwsem patches + this patch
- 7,954,545
Using perf-record(1), the %cpu time used by rwsem_down_write_slowpath(),
rwsem_down_write_failed() and their callees for the 3 kernels were 1.70%,
5.46% and 2.08% respectively.
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: [email protected]
Cc: Ingo Molnar <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: huang ying <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
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Security is a wonderful thing, but so is the ability to debug based on
lockdep warnings. This commit therefore makes lockdep lock addresses
visible in the clear.
Signed-off-by: Paul E. McKenney <[email protected]>
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Returning the pointer that was passed in allows us to write
slightly more idiomatic code. Convert a few users.
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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Report the number of stack traces and the number of stack trace hash
chains. These two numbers are useful because these allow to estimate
the number of stack trace hash collisions.
Signed-off-by: Bart Van Assche <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Will Deacon <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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Although commit 669de8bda87b ("kernel/workqueue: Use dynamic lockdep keys
for workqueues") unregisters dynamic lockdep keys when a workqueue is
destroyed, a side effect of that commit is that all stack traces
associated with the lockdep key are leaked when a workqueue is destroyed.
Fix this by storing each unique stack trace once. Other changes in this
patch are:
- Use NULL instead of { .nr_entries = 0 } to represent 'no trace'.
- Store a pointer to a stack trace in struct lock_class and struct
lock_list instead of storing 'nr_entries' and 'offset'.
This patch avoids that the following program triggers the "BUG:
MAX_STACK_TRACE_ENTRIES too low!" complaint:
#include <fcntl.h>
#include <unistd.h>
int main()
{
for (;;) {
int fd = open("/dev/infiniband/rdma_cm", O_RDWR);
close(fd);
}
}
Suggested-by: Peter Zijlstra <[email protected]>
Reported-by: Eric Biggers <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yuyang Du <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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modified
This patch does not change the behavior of the lockdep code.
Signed-off-by: Bart Van Assche <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Will Deacon <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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An uninitialized/ zeroed mutex will go unnoticed because there is no
check for it. There is a magic check in the unlock's slowpath path which
might go unnoticed if the unlock happens in the fastpath.
Add a ->magic check early in the mutex_lock() and mutex_trylock() path.
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Will Deacon <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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As Will Deacon points out, CONFIG_PROVE_LOCKING implies TRACE_IRQFLAGS,
so the conditions I added in the previous patch, and some others in the
same file can be simplified by only checking for the former.
No functional change.
Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Will Deacon <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Bart Van Assche <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Yuyang Du <[email protected]>
Fixes: 886532aee3cd ("locking/lockdep: Move mark_lock() inside CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING")
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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The usage is now hidden in an #ifdef, so we need to move
the variable itself in there as well to avoid this warning:
kernel/locking/lockdep_proc.c:203:21: error: unused variable 'class' [-Werror,-Wunused-variable]
Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Bart Van Assche <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Qian Cai <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yuyang Du <[email protected]>
Cc: [email protected]
Fixes: 68d41d8c94a3 ("locking/lockdep: Fix lock used or unused stats error")
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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Since we just reviewed read_slowpath for ACQUIRE correctness, add a
few coments to retain our findings.
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Will Deacon <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
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While reviewing another read_slowpath patch, both Will and I noticed
another missing ACQUIRE, namely:
X = 0;
CPU0 CPU1
rwsem_down_read()
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
X = 1;
rwsem_up_write();
rwsem_mark_wake()
atomic_long_add(adjustment, &sem->count);
smp_store_release(&waiter->task, NULL);
if (!waiter.task)
break;
...
}
r = X;
Allows 'r == 0'.
Reported-by: Peter Zijlstra (Intel) <[email protected]>
Reported-by: Will Deacon <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Will Deacon <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Ingo Molnar <[email protected]>
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LTP mtest06 has been observed to occasionally hit "still mapped when
deleted" and following BUG_ON on arm64.
The extra mapcount originated from pagefault handler, which handled
pagefault for vma that has already been detached. vma is detached
under mmap_sem write lock by detach_vmas_to_be_unmapped(), which
also invalidates vmacache.
When the pagefault handler (under mmap_sem read lock) calls
find_vma(), vmacache_valid() wrongly reports vmacache as valid.
After rwsem down_read() returns via 'queue empty' path (as of v5.2),
it does so without an ACQUIRE on sem->count:
down_read()
__down_read()
rwsem_down_read_failed()
__rwsem_down_read_failed_common()
raw_spin_lock_irq(&sem->wait_lock);
if (list_empty(&sem->wait_list)) {
if (atomic_long_read(&sem->count) >= 0) {
raw_spin_unlock_irq(&sem->wait_lock);
return sem;
The problem can be reproduced by running LTP mtest06 in a loop and
building the kernel (-j $NCPUS) in parallel. It does reproduces since
v4.20 on arm64 HPE Apollo 70 (224 CPUs, 256GB RAM, 2 nodes). It
triggers reliably in about an hour.
The patched kernel ran fine for 10+ hours.
Signed-off-by: Jan Stancek <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Will Deacon <[email protected]>
Acked-by: Waiman Long <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Fixes: 4b486b535c33 ("locking/rwsem: Exit read lock slowpath if queue empty & no writer")
Link: https://lkml.kernel.org/r/50b8914e20d1d62bb2dee42d342836c2c16ebee7.1563438048.git.jstancek@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>
|