md: fix deadlock between mddev_suspend() and md_write_start()

If mddev_suspend() races with md_write_start() we can deadlock
with mddev_suspend() waiting for the request that is currently
in md_write_start() to complete the ->make_request() call,
and md_write_start() waiting for the metadata to be updated
to mark the array as 'dirty'.
As metadata updates done by md_check_recovery() only happen then
the mddev_lock() can be claimed, and as mddev_suspend() is often
called with the lock held, these threads wait indefinitely for each
other.

We fix this by having md_write_start() abort if mddev_suspend()
is happening, and ->make_request() aborts if md_write_start()
aborted.
md_make_request() can detect this abort, decrease the ->active_io
count, and wait for mddev_suspend().

Reported-by: Nix <nix@esperi.org.uk>
Fix: 68866e425be2(MD: no sync IO while suspended)
Cc: stable@vger.kernel.org
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index e1a7e3d4c5e4..c71739b87ab7 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1321,7 +1321,6 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
          * Continue immediately if no resync is active currently.
          */
 
-        md_write_start(mddev, bio); /* wait on superblock update early */
 
         if ((bio_end_sector(bio) > mddev->suspend_lo &&
             bio->bi_iter.bi_sector < mddev->suspend_hi) ||
@@ -1550,13 +1549,13 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
         wake_up(&conf->wait_barrier);
 }
 
-static void raid1_make_request(struct mddev *mddev, struct bio *bio)
+static bool raid1_make_request(struct mddev *mddev, struct bio *bio)
 {
         sector_t sectors;
 
         if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
                 md_flush_request(mddev, bio);
-                return;
+                return true;
         }
 
         /*
@@ -1571,8 +1570,12 @@ static void raid1_make_request(struct mddev *mddev, struct bio *bio)
 
         if (bio_data_dir(bio) == READ)
                 raid1_read_request(mddev, bio, sectors, NULL);
-        else
+        else {
+                if (!md_write_start(mddev,bio))
+                        return false;
                 raid1_write_request(mddev, bio, sectors);
+        }
+        return true;
 }
 
 static void raid1_status(struct seq_file *seq, struct mddev *mddev)