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author | Peter Zijlstra <peterz@infradead.org> | 2012-05-15 08:06:19 -0700 |
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committer | Tejun Heo <tj@kernel.org> | 2012-05-15 08:08:31 -0700 |
commit | 4d82a1debbffec129cc387aafa8f40b7bbab3297 (patch) | |
tree | 64e7bc03962b99fa9b8c4cdb603d1784185a2a20 /include/linux/lockdep.h | |
parent | 544ecf310f0e7f51fa057ac2a295fc1b3b35a9d3 (diff) | |
download | linux-stable-4d82a1debbffec129cc387aafa8f40b7bbab3297.tar.gz linux-stable-4d82a1debbffec129cc387aafa8f40b7bbab3297.tar.bz2 linux-stable-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 'include/linux/lockdep.h')
-rw-r--r-- | include/linux/lockdep.h | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index d36619ead3ba..00e46376e28f 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -157,6 +157,24 @@ struct lockdep_map { #endif }; +static inline void lockdep_copy_map(struct lockdep_map *to, + struct lockdep_map *from) +{ + int i; + + *to = *from; + /* + * Since the class cache can be modified concurrently we could observe + * half pointers (64bit arch using 32bit copy insns). Therefore clear + * the caches and take the performance hit. + * + * XXX it doesn't work well with lockdep_set_class_and_subclass(), since + * that relies on cache abuse. + */ + for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++) + to->class_cache[i] = NULL; +} + /* * Every lock has a list of other locks that were taken after it. * We only grow the list, never remove from it: |