linux-kernel - [PATCH] [221/275] aio: wake all waiters when destroying ctx

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Message-Id: <20110330210746.602FF3E1A05@tassilo.jf.intel.com>
Date:	Wed, 30 Mar 2011 14:07:46 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	roland@...estorage.com, ak@...ux.intel.com, jmoyer@...hat.com,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	gregkh@...e.de, linux-kernel@...r.kernel.org, stable@...nel.org,
	tim.bird@...sony.com
Subject: [PATCH] [221/275] aio: wake all waiters when destroying ctx

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Roland Dreier <roland@...estorage.com>

commit e91f90bb0bb10be9cc8efd09a3cf4ecffcad0db1 upstream.

The test program below will hang because io_getevents() uses
add_wait_queue_exclusive(), which means the wake_up() in io_destroy() only
wakes up one of the threads.  Fix this by using wake_up_all() in the aio
code paths where we want to make sure no one gets stuck.

	// t.c -- compile with gcc -lpthread -laio t.c

	#include <libaio.h>
	#include <pthread.h>
	#include <stdio.h>
	#include <unistd.h>

	static const int nthr = 2;

	void *getev(void *ctx)
	{
		struct io_event ev;
		io_getevents(ctx, 1, 1, &ev, NULL);
		printf("io_getevents returned\n");
		return NULL;
	}

	int main(int argc, char *argv[])
	{
		io_context_t ctx = 0;
		pthread_t thread[nthr];
		int i;

		io_setup(1024, &ctx);

		for (i = 0; i < nthr; ++i)
			pthread_create(&thread[i], NULL, getev, ctx);

		sleep(1);

		io_destroy(ctx);

		for (i = 0; i < nthr; ++i)
			pthread_join(thread[i], NULL);

		return 0;
	}

Signed-off-by: Roland Dreier <roland@...estorage.com>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Reviewed-by: Jeff Moyer <jmoyer@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/aio.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux-2.6.35.y/fs/aio.c
===================================================================
--- linux-2.6.35.y.orig/fs/aio.c	2011-03-29 22:50:28.449530467 -0700
+++ linux-2.6.35.y/fs/aio.c	2011-03-29 23:03:02.843227419 -0700
@@ -512,7 +512,7 @@
 	ctx->reqs_active--;
 
 	if (unlikely(!ctx->reqs_active && ctx->dead))
-		wake_up(&ctx->wait);
+		wake_up_all(&ctx->wait);
 }
 
 static void aio_fput_routine(struct work_struct *data)
@@ -1233,7 +1233,7 @@
 	 * by other CPUs at this point.  Right now, we rely on the
 	 * locking done by the above calls to ensure this consistency.
 	 */
-	wake_up(&ioctx->wait);
+	wake_up_all(&ioctx->wait);
 	put_ioctx(ioctx);	/* once for the lookup */
 }
 
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