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| author | Frederic Weisbecker <frederic@kernel.org> | 2024-05-30 15:45:46 +0200 |
|---|---|---|
| committer | Neeraj Upadhyay <neeraj.upadhyay@kernel.org> | 2024-07-29 07:34:31 +0530 |
| commit | 4e26ce423116e9f48f73723cc33add295e56ad31 (patch) | |
| tree | 8fd07d1103d07ca79f91290b9d9ec83d809e196f /lib/test_fortify/write_overflow-memmove.c | |
| parent | 7121dd915a262aee1f5a88cf86b1543f3a9439d7 (diff) | |
rcu/nocb: (De-)offload callbacks on offline CPUs only
Currently callbacks can be (de-)offloaded only on online CPUs. This
involves an overly elaborated state machine in order to make sure that
callbacks are always handled during the process while ensuring
synchronization between rcu_core and NOCB kthreads.
The only potential user of NOCB (de-)offloading appears to be a
nohz_full toggling interface through cpusets. And the general agreement
is now to work toward toggling the nohz_full state on offline CPUs to
simplify the whole picture.
Therefore, convert the (de-)offloading to only support offline CPUs.
This involves the following changes:
* Call rcu_barrier() before deoffloading. An offline offloaded CPU may
still carry callbacks in its queue ignored by
rcutree_migrate_callbacks(). Those callbacks must all be flushed
before switching to a regular queue because no more kthreads will
handle those before the CPU ever gets re-onlined.
This means that further calls to rcu_barrier() will find an empty
queue until the CPU goes through rcutree_report_cpu_starting(). As a
result it is guaranteed that further rcu_barrier() won't try to lock
the nocb_lock for that target and thus won't risk an imbalance.
Therefore barrier_mutex doesn't need to be locked anymore upon
deoffloading.
* Assume the queue is empty before offloading, as
rcutree_migrate_callbacks() took care of everything.
This means that further calls to rcu_barrier() will find an empty
queue until the CPU goes through rcutree_report_cpu_starting(). As a
result it is guaranteed that further rcu_barrier() won't risk a
nocb_lock imbalance.
Therefore barrier_mutex doesn't need to be locked anymore upon
offloading.
* No need to flush bypass anymore.
Further simplifications will follow in upcoming patches.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Diffstat (limited to 'lib/test_fortify/write_overflow-memmove.c')
0 files changed, 0 insertions, 0 deletions