lkml.org 
[lkml]   [2011]   [Oct]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: WARNING: at kernel/lockdep.c:690 __lock_acquire+0x168/0x164b()
On Fri, Oct 21, 2011 at 02:14:34AM -0700, David Rientjes wrote:
> How does it mask the race condition? Before the memset(), the ->name
> field was never _cleared_ in lockdep_init_map() like it is now, it was
> only stored.

A typcal race condition will like this:

CPU A CPU B
lock_set_subclass(lockA);
lock_set_class(lockA);
lockdep_init_map(lockA);
/* lockA->name is cleared */
memset(lockA);
__lock_acquire(lockA);
/* lockA->class_cache[] is cleared */
register_lock_class(lockA);
look_up_lock_class(lockA);
WARN_ON_ONCE(class->name !=
lock->name);

lock->name = name;

And a untested patch is below:
BTW, now the patch could cure (I guess) the very issue reported
in this thread.
But it don't cover the case which change the key and the relevant
lock_class has existed, I don't think out a way how to fix it yet :)
But the fact is we have no such caller yet, the only call site of
lock_set_subclass() is double_unlock_balance().

Thanks,
Yong

---
From: Yong Zhang <yong.zhang0@gmail.com>
Subject: [PATCH] lockdep: On-demand initialization for lock_set_class()

Since commit f59de89 [lockdep: Clear whole lockdep_map on initialization],
lockdep_init_map() will clear all the struct. But it will break
lock_set_class()/lock_set_subclass(). A typical race condition
is like below:

CPU A CPU B
lock_set_subclass(lockA);
lock_set_class(lockA);
lockdep_init_map(lockA);
/* lockA->name is cleared */
memset(lockA);
__lock_acquire(lockA);
/* lockA->class_cache[] is cleared */
register_lock_class(lockA);
look_up_lock_class(lockA);
WARN_ON_ONCE(class->name !=
lock->name);

lock->name = name;

Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
---
kernel/lockdep.c | 5 ++++-
1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 91d67ce..bc7dd1e 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -3160,7 +3160,10 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
return print_unlock_inbalance_bug(curr, lock, ip);

found_it:
- lockdep_init_map(lock, name, key, 0);
+ /* only changing lock->name make no sense */
+ WARN_ON(lock->key == key && lock->name != name);
+ if (lock->key != key)
+ lockdep_init_map(lock, name, key, 0);
class = register_lock_class(lock, subclass, 0);
hlock->class_idx = class - lock_classes + 1;

--
1.7.5.4



\
 
 \ /
  Last update: 2011-10-21 11:47    [W:0.064 / U:7.724 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site