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aio: fix rcu ioctx lookup

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aio-dio-invalidate-failure GPFs in aio_put_req from io_submit.

lookup_ioctx doesn't implement the rcu lookup pattern properly.
rcu_read_lock does not prevent refcount going to zero, so we might take
a refcount on a zero count ioctx.

Fix the bug by atomically testing for zero refcount before incrementing.

[jack@suse.cz: added comment into the code]
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Piggin 2011-02-25 14:44:26 -08:00 committed by Linus Torvalds
parent 29723fccc8
commit 3bd9a5d734
1 changed files with 24 additions and 11 deletions
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35
fs/aio.c
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@ -239,15 +239,23 @@ static void __put_ioctx(struct kioctx *ctx)
call_rcu(&ctx->rcu_head, ctx_rcu_free);
}
#define get_ioctx(kioctx) do { \
BUG_ON(atomic_read(&(kioctx)->users) <= 0); \
atomic_inc(&(kioctx)->users); \
} while (0)
#define put_ioctx(kioctx) do { \
BUG_ON(atomic_read(&(kioctx)->users) <= 0); \
if (unlikely(atomic_dec_and_test(&(kioctx)->users))) \
__put_ioctx(kioctx); \
} while (0)
static inline void get_ioctx(struct kioctx *kioctx)
{
BUG_ON(atomic_read(&kioctx->users) <= 0);
atomic_inc(&kioctx->users);
}
static inline int try_get_ioctx(struct kioctx *kioctx)
{
return atomic_inc_not_zero(&kioctx->users);
}
static inline void put_ioctx(struct kioctx *kioctx)
{
BUG_ON(atomic_read(&kioctx->users) <= 0);
if (unlikely(atomic_dec_and_test(&kioctx->users)))
__put_ioctx(kioctx);
}
/* ioctx_alloc
* Allocates and initializes an ioctx. Returns an ERR_PTR if it failed.
@ -601,8 +609,13 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
rcu_read_lock();
hlist_for_each_entry_rcu(ctx, n, &mm->ioctx_list, list) {
if (ctx->user_id == ctx_id && !ctx->dead) {
get_ioctx(ctx);
/*
* RCU protects us against accessing freed memory but
* we have to be careful not to get a reference when the
* reference count already dropped to 0 (ctx->dead test
* is unreliable because of races).
*/
if (ctx->user_id == ctx_id && !ctx->dead && try_get_ioctx(ctx)){
ret = ctx;
break;
}