Commit 65c24491 authored Mar 18, 2009 by Jeff Moyer Committed by Linus Torvalds Mar 19, 2009

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 abf137dd).

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 <jmoyer@redhat.com>
Acked-by: Zach Brown <zach.brown@oracle.com>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 87c3a86e

fs/aio.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}

		/*

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