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| author | Peter Zijlstra <peterz@infradead.org> | 2012-05-15 08:06:19 -0700 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2012-05-15 08:08:31 -0700 |
| commit | 4d82a1debbffec129cc387aafa8f40b7bbab3297 (patch) | |
| tree | 64e7bc03962b99fa9b8c4cdb603d1784185a2a20 /kernel/timer.c | |
| parent | 544ecf310f0e7f51fa057ac2a295fc1b3b35a9d3 (diff) | |
| download | lwn-4d82a1debbffec129cc387aafa8f40b7bbab3297.tar.gz lwn-4d82a1debbffec129cc387aafa8f40b7bbab3297.zip | |
lockdep: fix oops in processing workqueue
Under memory load, on x86_64, with lockdep enabled, the workqueue's
process_one_work() has been seen to oops in __lock_acquire(), barfing
on a 0xffffffff00000000 pointer in the lockdep_map's class_cache[].
Because it's permissible to free a work_struct from its callout function,
the map used is an onstack copy of the map given in the work_struct: and
that copy is made without any locking.
Surprisingly, gcc (4.5.1 in Hugh's case) uses "rep movsl" rather than
"rep movsq" for that structure copy: which might race with a workqueue
user's wait_on_work() doing lock_map_acquire() on the source of the
copy, putting a pointer into the class_cache[], but only in time for
the top half of that pointer to be copied to the destination map.
Boom when process_one_work() subsequently does lock_map_acquire()
on its onstack copy of the lockdep_map.
Fix this, and a similar instance in call_timer_fn(), with a
lockdep_copy_map() function which additionally NULLs the class_cache[].
Note: this oops was actually seen on 3.4-next, where flush_work() newly
does the racing lock_map_acquire(); but Tejun points out that 3.4 and
earlier are already vulnerable to the same through wait_on_work().
* Patch orginally from Peter. Hugh modified it a bit and wrote the
description.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Reported-by: Hugh Dickins <hughd@google.com>
LKML-Reference: <alpine.LSU.2.00.1205070951170.1544@eggly.anvils>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/timer.c')
| -rw-r--r-- | kernel/timer.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/kernel/timer.c b/kernel/timer.c index a297ffcf888e..b12385244bb5 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -1102,7 +1102,9 @@ static void call_timer_fn(struct timer_list *timer, void (*fn)(unsigned long), * warnings as well as problems when looking into * timer->lockdep_map, make a copy and use that here. */ - struct lockdep_map lockdep_map = timer->lockdep_map; + struct lockdep_map lockdep_map; + + lockdep_copy_map(&lockdep_map, &timer->lockdep_map); #endif /* * Couple the lock chain with the lock chain at |