aio: wake all waiters when destroying ctx

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@purestorage.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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 */
 }