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    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



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