Patch "aio: fix serial draining in exit_aio()" has been added to the 4.0-stable tree

Patch "aio: fix serial draining in exit_aio()" has been added to the 4.0-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    aio: fix serial draining in exit_aio()

to the 4.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     aio-fix-serial-draining-in-exit_aio.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From dc48e56d761610da4ea1088d1bea0a030b8e3e43 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Wed, 15 Apr 2015 11:17:23 -0600
Subject: aio: fix serial draining in exit_aio()

From: Jens Axboe <axboe@fb.com>

commit dc48e56d761610da4ea1088d1bea0a030b8e3e43 upstream.

exit_aio() currently serializes killing io contexts. Each context
killing ends up having to do percpu_ref_kill(), which in turns has
to wait for an RCU grace period. This can take a long time, depending
on the number of contexts. And there's no point in doing them serially,
when we could be waiting for all of them in one fell swoop.

This patches makes my fio thread offload test case exit 0.2s instead
of almost 6s.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/aio.c |   45 ++++++++++++++++++++++++++++++---------------
 1 file changed, 30 insertions(+), 15 deletions(-)

--- a/fs/aio.c
+++ b/fs/aio.c
@@ -77,6 +77,11 @@ struct kioctx_cpu {
 	unsigned		reqs_available;
 };
 
+struct ctx_rq_wait {
+	struct completion comp;
+	atomic_t count;
+};
+
 struct kioctx {
 	struct percpu_ref	users;
 	atomic_t		dead;
@@ -115,7 +120,7 @@ struct kioctx {
 	/*
 	 * signals when all in-flight requests are done
 	 */
-	struct completion *requests_done;
+	struct ctx_rq_wait	*rq_wait;
 
 	struct {
 		/*
@@ -539,8 +544,8 @@ static void free_ioctx_reqs(struct percp
 	struct kioctx *ctx = container_of(ref, struct kioctx, reqs);
 
 	/* At this point we know that there are no any in-flight requests */
-	if (ctx->requests_done)
-		complete(ctx->requests_done);
+	if (ctx->rq_wait && atomic_dec_and_test(&ctx->rq_wait->count))
+		complete(&ctx->rq_wait->comp);
 
 	INIT_WORK(&ctx->free_work, free_ioctx);
 	schedule_work(&ctx->free_work);
@@ -751,7 +756,7 @@ err:
  *	the rapid destruction of the kioctx.
  */
 static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
-		struct completion *requests_done)
+		      struct ctx_rq_wait *wait)
 {
 	struct kioctx_table *table;
 
@@ -781,7 +786,7 @@ static int kill_ioctx(struct mm_struct *
 	if (ctx->mmap_size)
 		vm_munmap(ctx->mmap_base, ctx->mmap_size);
 
-	ctx->requests_done = requests_done;
+	ctx->rq_wait = wait;
 	percpu_ref_kill(&ctx->users);
 	return 0;
 }
@@ -813,18 +818,24 @@ EXPORT_SYMBOL(wait_on_sync_kiocb);
 void exit_aio(struct mm_struct *mm)
 {
 	struct kioctx_table *table = rcu_dereference_raw(mm->ioctx_table);
-	int i;
+	struct ctx_rq_wait wait;
+	int i, skipped;
 
 	if (!table)
 		return;
 
+	atomic_set(&wait.count, table->nr);
+	init_completion(&wait.comp);
+
+	skipped = 0;
 	for (i = 0; i < table->nr; ++i) {
 		struct kioctx *ctx = table->table[i];
-		struct completion requests_done =
-			COMPLETION_INITIALIZER_ONSTACK(requests_done);
 
-		if (!ctx)
+		if (!ctx) {
+			skipped++;
 			continue;
+		}
+
 		/*
 		 * We don't need to bother with munmap() here - exit_mmap(mm)
 		 * is coming and it'll unmap everything. And we simply can't,
@@ -833,10 +844,12 @@ void exit_aio(struct mm_struct *mm)
 		 * that it needs to unmap the area, just set it to 0.
 		 */
 		ctx->mmap_size = 0;
-		kill_ioctx(mm, ctx, &requests_done);
+		kill_ioctx(mm, ctx, &wait);
+	}
 
+	if (!atomic_sub_and_test(skipped, &wait.count)) {
 		/* Wait until all IO for the context are done. */
-		wait_for_completion(&requests_done);
+		wait_for_completion(&wait.comp);
 	}
 
 	RCU_INIT_POINTER(mm->ioctx_table, NULL);
@@ -1321,15 +1334,17 @@ SYSCALL_DEFINE1(io_destroy, aio_context_
 {
 	struct kioctx *ioctx = lookup_ioctx(ctx);
 	if (likely(NULL != ioctx)) {
-		struct completion requests_done =
-			COMPLETION_INITIALIZER_ONSTACK(requests_done);
+		struct ctx_rq_wait wait;
 		int ret;
 
+		init_completion(&wait.comp);
+		atomic_set(&wait.count, 1);
+
 		/* Pass requests_done to kill_ioctx() where it can be set
 		 * in a thread-safe way. If we try to set it here then we have
 		 * a race condition if two io_destroy() called simultaneously.
 		 */
-		ret = kill_ioctx(current->mm, ioctx, &requests_done);
+		ret = kill_ioctx(current->mm, ioctx, &wait);
 		percpu_ref_put(&ioctx->users);
 
 		/* Wait until all IO for the context are done. Otherwise kernel
@@ -1337,7 +1352,7 @@ SYSCALL_DEFINE1(io_destroy, aio_context_
 		 * is destroyed.
 		 */
 		if (!ret)
-			wait_for_completion(&requests_done);
+			wait_for_completion(&wait.comp);
 
 		return ret;
 	}


Patches currently in stable-queue which might be from axboe@fb.com are

queue-4.0/aio-fix-serial-draining-in-exit_aio.patch