dm mpath: take m->lock spinlock when testing QUEUE_IF_NO_PATH

Fix multipath_end_io, multipath_end_io_bio and multipath_busy to take
m->lock while testing if MPATHF_QUEUE_IF_NO_PATH bit is set.  These are
all slow-path cases when no paths are available so extra locking isn't a
performance hit.  Correctness matters most.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index d7bb74b..bf51758 100644 (file)
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1621,12 +1621,16 @@ static int multipath_end_io(struct dm_target *ti, struct request *clone,
                if (pgpath)
                        fail_path(pgpath);
 
-               if (atomic_read(&m->nr_valid_paths) == 0 &&
-                   !must_push_back_rq(m)) {
-                       if (error == BLK_STS_IOERR)
-                               dm_report_EIO(m);
-                       /* complete with the original error */
-                       r = DM_ENDIO_DONE;
+               if (!atomic_read(&m->nr_valid_paths)) {
+                       unsigned long flags;
+                       spin_lock_irqsave(&m->lock, flags);
+                       if (!must_push_back_rq(m)) {
+                               if (error == BLK_STS_IOERR)
+                                       dm_report_EIO(m);
+                               /* complete with the original error */
+                               r = DM_ENDIO_DONE;
+                       }
+                       spin_unlock_irqrestore(&m->lock, flags);
                }
        }
 
@@ -1656,15 +1660,19 @@ static int multipath_end_io_bio(struct dm_target *ti, struct bio *clone,
        if (pgpath)
                fail_path(pgpath);
 
-       if (atomic_read(&m->nr_valid_paths) == 0 &&
-           !test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
-               if (__must_push_back(m)) {
-                       r = DM_ENDIO_REQUEUE;
-               } else {
-                       dm_report_EIO(m);
-                       *error = BLK_STS_IOERR;
+       if (!atomic_read(&m->nr_valid_paths)) {
+               spin_lock_irqsave(&m->lock, flags);
+               if (!test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
+                       if (__must_push_back(m)) {
+                               r = DM_ENDIO_REQUEUE;
+                       } else {
+                               dm_report_EIO(m);
+                               *error = BLK_STS_IOERR;
+                       }
+                       spin_unlock_irqrestore(&m->lock, flags);
+                       goto done;
                }
-               goto done;
+               spin_unlock_irqrestore(&m->lock, flags);
        }
 
        spin_lock_irqsave(&m->lock, flags);
@@ -1962,10 +1970,11 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
                }
        } else {
                /* No path is available */
+               r = -EIO;
+               spin_lock_irqsave(&m->lock, flags);
                if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
                        r = -ENOTCONN;
-               else
-                       r = -EIO;
+               spin_unlock_irqrestore(&m->lock, flags);
        }
 
        if (r == -ENOTCONN) {
@@ -2036,8 +2045,15 @@ static int multipath_busy(struct dm_target *ti)
                return true;
 
        /* no paths available, for blk-mq: rely on IO mapping to delay requeue */
-       if (!atomic_read(&m->nr_valid_paths) && test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
-               return (m->queue_mode != DM_TYPE_REQUEST_BASED);
+       if (!atomic_read(&m->nr_valid_paths)) {
+               unsigned long flags;
+               spin_lock_irqsave(&m->lock, flags);
+               if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
+                       spin_unlock_irqrestore(&m->lock, flags);
+                       return (m->queue_mode != DM_TYPE_REQUEST_BASED);
+               }
+               spin_unlock_irqrestore(&m->lock, flags);
+       }
 
        /* Guess which priority_group will be used at next mapping time */
        pg = READ_ONCE(m->current_pg);