From 65c24491b4fef017c64e39ec64384fde5e05e0a0 Mon Sep 17 00:00:00 2001 From: Jeff Moyer Date: Wed, 18 Mar 2009 17:04:21 -0700 Subject: [PATCH] aio: lookup_ioctx can return the wrong value when looking up a bogus context The libaio test harness turned up a problem whereby lookup_ioctx on a bogus io context was returning the 1 valid io context from the list (harness/cases/3.p). Because of that, an extra put_iocontext was done, and when the process exited, it hit a BUG_ON in the put_iocontext macro called from exit_aio (since we expect a users count of 1 and instead get 0). The problem was introduced by "aio: make the lookup_ioctx() lockless" (commit abf137dd7712132ee56d5b3143c2ff61a72a5faa). Thanks to Zach for pointing out that hlist_for_each_entry_rcu will not return with a NULL tpos at the end of the loop, even if the entry was not found. Signed-off-by: Jeff Moyer Acked-by: Zach Brown Acked-by: Jens Axboe Cc: Benjamin LaHaise Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/aio.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/fs/aio.c b/fs/aio.c index 4a9d4d641fb9..76da12537956 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -587,7 +587,7 @@ int aio_put_req(struct kiocb *req) static struct kioctx *lookup_ioctx(unsigned long ctx_id) { struct mm_struct *mm = current->mm; - struct kioctx *ctx = NULL; + struct kioctx *ctx, *ret = NULL; struct hlist_node *n; rcu_read_lock(); @@ -595,12 +595,13 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id) hlist_for_each_entry_rcu(ctx, n, &mm->ioctx_list, list) { if (ctx->user_id == ctx_id && !ctx->dead) { get_ioctx(ctx); + ret = ctx; break; } } rcu_read_unlock(); - return ctx; + return ret; } /*