lkml.org 
[lkml]   [2009]   [Jun]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] LIB: remove unmatched write_lock() in gen_pool_destroy
On Fri, 12 Jun 2009, Zygo Blaxell wrote:

> Fix mismatch between calls to write_lock() and write_unlock() in
> gen_pool_destroy by removing the write_lock().
>
> Signed-off-by: Zygo Blaxell <zygo.blaxell@xandros.com>
> ---
> There is a call to write_lock() in gen_pool_destroy which is not balanced
> by any corresponding write_unlock(). This causes problems with preemption
> because the preemption-disable counter is incremented in the write_lock()
> call, but never decremented by any call to write_unlock(). This bug is
> difficult to observe in the field because only two in-tree drivers call
> gen_pool_destroy, and one of them is non-x86 arch-specific code.
>
> To fix this, I have chosen removing the write_lock() over adding a
> write_unlock() because the lock in question is inside a structure which
> is being freed. Any other thread that waited to acquire such a lock
> while gen_pool_destroy was running would find itself holding a lock
> in recently-freed or about-to-be-freed memory. This would result in
> memory corruption or a crash whether &pool->lock is held or not.
>
> Using a pool while it is in the process of being destroyed is a bug that
> must be resolved outside of the gen_pool_destroy function.
>
> lib/genalloc.c | 1 -
> 1 files changed, 0 insertions(+), 1 deletions(-)
>
> diff --git a/lib/genalloc.c b/lib/genalloc.c
> index f6d276d..eed2bdb 100644
> --- a/lib/genalloc.c
> +++ b/lib/genalloc.c
> @@ -85,7 +85,6 @@ void gen_pool_destroy(struct gen_pool *pool)
> int bit, end_bit;
>
>
> - write_lock(&pool->lock);
> list_for_each_safe(_chunk, _next_chunk, &pool->chunks) {
> chunk = list_entry(_chunk, struct gen_pool_chunk, next_chunk);
> list_del(&chunk->next_chunk);
> --
> 1.5.6.5
>

Hi Zygo,

this doesn't really qualify for trivial tree, as it introduces a
significant code change. Adding some CCs.

Thanks,

--
Jiri Kosina
SUSE Labs



\
 
 \ /
  Last update: 2009-06-15 23:39    [W:0.105 / U:0.272 seconds]
©2003-2014 Jasper Spaans. Advertise on this site