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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Mike Snitzer" <snitzer@redhat.com>,
        "Mikulas Patocka" <mpatocka@redhat.com>
Date:   Sun, 11 Nov 2018 19:49:05 +0000
Message-ID: <lsq.1541965745.522563766@decadent.org.uk>
Subject: [PATCH 3.16 329/366] dm bufio: drop the lock when doing GFP_NOIO
 allocation
In-Reply-To: <lsq.1541965744.387173642@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@redhat.com>

commit 41c73a49df31151f4ff868f28fe4f129f113fa2c upstream.

If the first allocation attempt using GFP_NOWAIT fails, drop the lock
and retry using GFP_NOIO allocation (lock is dropped because the
allocation can take some time).

Note that we won't do GFP_NOIO allocation when we loop for the second
time, because the lock shouldn't be dropped between __wait_for_free_buffer
and __get_unclaimed_buffer.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/md/dm-bufio.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -773,6 +773,7 @@ enum new_flag {
 static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client *c, enum new_flag nf)
 {
 	struct dm_buffer *b;
+	bool tried_noio_alloc = false;
 
 	/*
 	 * dm-bufio is resistant to allocation failures (it just keeps
@@ -797,6 +798,15 @@ static struct dm_buffer *__alloc_buffer_
 		if (nf == NF_PREFETCH)
 			return NULL;
 
+		if (dm_bufio_cache_size_latch != 1 && !tried_noio_alloc) {
+			dm_bufio_unlock(c);
+			b = alloc_buffer(c, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			dm_bufio_lock(c);
+			if (b)
+				return b;
+			tried_noio_alloc = true;
+		}
+
 		if (!list_empty(&c->reserved_buffers)) {
 			b = list_entry(c->reserved_buffers.next,
 				       struct dm_buffer, lru_list);