linux-kernel - [PATCH] aio: v3: fix kioctx not being freed after cancellation at exit time

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Date:	Fri, 15 Feb 2013 11:18:19 -0500
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] aio: v3: fix kioctx not being freed after cancellation at exit time

v3 corrects a typo in v2 of this patch.  The wrong version of the patch was
copied over and misspelled ctx in the first hunk.  A known good tree with
this patch is at git://git.kvack.org/~bcrl/linux-next-20130213.git-v3 .

This v2 patch replaces both "aio: fix kioctx not being freed after
cancellation at exit time" and "aio: only suppress events from cancelled
kiocbs if free_ioctx() is in progress".  Kent's feedback is indeed correct.

The recent changes overhauling fs/aio.c introduced a bug that results in the
kioctx not being freed when outstanding kiocbs are cancelled at exit_aio()
time.  Specifically, a kiocb that is cancelled has its completion events
discarded by batch_complete_aio(), which then fails to wake up the process
stuck in free_ioctx().  Fix this by removing the event suppression in
batch_complete_aio() and modify the wait_event() condition in free_ioctx()
appropriately.

This patch was tested with the cancel operation in the thread based code
posted yesterday.

Signed-off-by: Benjamin LaHaise <bcrl@...ck.org>
---
 fs/aio.c |   15 +++------------
 1 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index dc52b0c..2512232 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -335,7 +335,9 @@ static void free_ioctx(struct kioctx *ctx)
 	kunmap_atomic(ring);

 	while (atomic_read(&ctx->reqs_available) < ctx->nr) {
-		wait_event(ctx->wait, head != ctx->shadow_tail);
+		wait_event(ctx->wait,
+			   (head != ctx->shadow_tail) ||
+			   (atomic_read(&ctx->reqs_available) >= ctx->nr));

 		avail = (head <= ctx->shadow_tail ?
 			 ctx->shadow_tail : ctx->nr) - head;
@@ -747,17 +749,6 @@ void batch_complete_aio(struct batch_complete *batch)
 			n = rb_parent(n);
 		}

-		if (unlikely(xchg(&req->ki_cancel,
-				  KIOCB_CANCELLED) == KIOCB_CANCELLED)) {
-			/*
-			 * Can't use the percpu reqs_available here - could race
-			 * with free_ioctx()
-			 */
-			atomic_inc(&req->ki_ctx->reqs_available);
-			aio_put_req(req);
-			continue;
-		}
-
 		if (unlikely(req->ki_eventfd != eventfd)) {
 			if (eventfd) {
 				/* Make event visible */
-- 
1.7.4.1

-- 
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