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authorPeter Zijlstra <peterz@infradead.org>2012-05-15 08:06:19 -0700
committerTejun Heo <tj@kernel.org>2012-05-15 08:08:31 -0700
commit4d82a1debbffec129cc387aafa8f40b7bbab3297 (patch)
tree64e7bc03962b99fa9b8c4cdb603d1784185a2a20 /include/linux/lockdep.h
parent544ecf310f0e7f51fa057ac2a295fc1b3b35a9d3 (diff)
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.h18
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: