linux-kernel - [PATCH] aio: Wake all waiters when destroying ctx

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Message-Id: <1299822937-6522-1-git-send-email-roland@kernel.org>
Date:	Thu, 10 Mar 2011 21:55:37 -0800
From:	Roland Dreier <roland@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-aio@...ck.org, linux-kernel@...r.kernel.org,
	Benjamin LaHaise <bcrl@...ck.org>,
	Jeff Moyer <jmoyer@...hat.com>
Subject: [PATCH] aio: Wake all waiters when destroying ctx

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

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;
	}

Cc: <stable@...nel.org>
Signed-off-by: Roland Dreier <roland@...estorage.com>
---
 fs/aio.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 26869cd..88f0ed5 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -520,7 +520,7 @@ static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
 	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)
@@ -1229,7 +1229,7 @@ static void io_destroy(struct kioctx *ioctx)
 	 * 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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