[PATCH 3.16 329/366] dm bufio: drop the lock when doing GFP_NOIO allocation

[Ben Hutchings]

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

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

From: Mikulas Patocka <mpato...@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 <mpato...@redhat.com>
Signed-off-by: Mike Snitzer <snit...@redhat.com>
Cc: Mikulas Patocka <mpato...@redhat.com>
Signed-off-by: Ben Hutchings <b...@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);