linux-kernel - [PATCH] aio: only suppress events from cancelled kiocbs if free

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Message-ID: <20130213215214.GA24582@kvack.org>
Date:	Wed, 13 Feb 2013 16:52:14 -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: only suppress events from cancelled kiocbs if free_ioctx() is in progress

The io_cancel() syscall allows for cancellation of iocbs in flight to
generate a completion event.  The current behaviour of batch_complete_aio()
is to suppress all completion events.  Some types of asynchronous operations
cannot be cancelled synchronously, and must generate a completion event at
some point after the io_cancel() syscall.  Instead, only suppress
completion events during kioctx teardown by free_ioctx().

Signed-off-by: Benjamin LaHaise <bcrl@...ck.org>
---
 fs/aio.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 46f9dd0..1bcb818 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -81,6 +81,7 @@ struct kioctx {
 
 	/* sys_io_setup currently limits this to an unsigned int */
 	unsigned		max_reqs;
+	unsigned		dead;
 
 	unsigned long		mmap_base;
 	unsigned long		mmap_size;
@@ -311,6 +312,7 @@ static void free_ioctx(struct kioctx *ctx)
 	struct kiocb *req;
 	unsigned cpu, head, avail;
 
+	ctx->dead = 1;
 	spin_lock_irq(&ctx->ctx_lock);
 
 	while (!list_empty(&ctx->active_reqs)) {
@@ -749,7 +751,9 @@ void batch_complete_aio(struct batch_complete *batch)
 			n = rb_parent(n);
 		}
 
-		if (unlikely(xchg(&req->ki_cancel,
+		/* Suppress cancelled events if free_ioctx() is in progress. */
+		if (unlikely(req->ki_ctx->dead &&
+			     xchg(&req->ki_cancel,
 				  KIOCB_CANCELLED) == KIOCB_CANCELLED)) {
 			/*
 			 * Can't use the percpu reqs_available here - could race
-- 
1.7.4.1


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