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SubjectRe: [PATCH] LIB: remove unmatched write_lock() in gen_pool_destroy

Jiri Kosina wrote:
> 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.
>
>

Looks ok to me. Its dumb to aquire the lock you're gonna free anyway.
Maybe some BUG_ON() that sez nobody better be holding this lock?





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