lockdep: Fix a race between /proc/lock_stat and module unload

The lock_class iteration of /proc/lock_stat is not serialized against
the lockdep_free_key_range() call from module unload.

Therefore it can happen that we find a class of which ->name/->key are
no longer valid.

There is a further bug in zap_class() that left ->name dangling. Cure
this. Use RCU_INIT_POINTER() because NULL.

Since lockdep_free_key_range() is rcu_sched serialized, we can read
both ->name and ->key under rcu_read_lock_sched() (preempt-disable)
and be assured that if we observe a !NULL value it stays safe to use
for as long as we hold that lock.

If we observe both NULL, skip the entry.

Reported-by: Jerome Marchand <[email protected]>
Tested-by: Jerome Marchand <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions