dm mpath: fix bio-based multipath queue_if_no_path handling

Commit ca5beb76 ("dm mpath: micro-optimize the hot path relative to
MPATHF_QUEUE_IF_NO_PATH") caused bio-based DM-multipath to fail mptest's
"test_02_sdev_delete".

Restoring the logic that existed prior to commit ca5beb76 fixes this
bio-based DM-multipath regression.  Also verified all mptest tests pass
with request-based DM-multipath.

This commit effectively reverts commit ca5beb76 -- but it does so
without reintroducing the need to take the m->lock spinlock in
must_push_back_{rq,bio}.

Fixes: ca5beb76 ("dm mpath: micro-optimize the hot path relative to MPATHF_QUEUE_IF_NO_PATH")
Cc: stable@vger.kernel.org # 4.12+
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 42 insertions, 7 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 35a2a2fa477f..f7810cc869ac 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -458,6 +458,38 @@ do {									\
 } while (0)
 
 /*
+ * Check whether bios must be queued in the device-mapper core rather
+ * than here in the target.
+ *
+ * If MPATHF_QUEUE_IF_NO_PATH and MPATHF_SAVED_QUEUE_IF_NO_PATH hold
+ * the same value then we are not between multipath_presuspend()
+ * and multipath_resume() calls and we have no need to check
+ * for the DMF_NOFLUSH_SUSPENDING flag.
+ */
+static bool __must_push_back(struct multipath *m, unsigned long flags)
+{
+        return ((test_bit(MPATHF_QUEUE_IF_NO_PATH, &flags) !=
+                 test_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &flags)) &&
+                dm_noflush_suspending(m->ti));
+}
+
+/*
+ * Following functions use READ_ONCE to get atomic access to
+ * all m->flags to avoid taking spinlock
+ */
+static bool must_push_back_rq(struct multipath *m)
+{
+        unsigned long flags = READ_ONCE(m->flags);
+        return test_bit(MPATHF_QUEUE_IF_NO_PATH, &flags) || __must_push_back(m, flags);
+}
+
+static bool must_push_back_bio(struct multipath *m)
+{
+        unsigned long flags = READ_ONCE(m->flags);
+        return __must_push_back(m, flags);
+}
+
+/*
  * Map cloned requests (request-based multipath)
  */
 static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
@@ -478,7 +510,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
                 pgpath = choose_pgpath(m, nr_bytes);
 
         if (!pgpath) {
-                if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
+                if (must_push_back_rq(m))
                         return DM_MAPIO_DELAY_REQUEUE;
                 dm_report_EIO(m);       /* Failed */
                 return DM_MAPIO_KILL;
@@ -553,7 +585,7 @@ static int __multipath_map_bio(struct multipath *m, struct bio *bio, struct dm_m
         }
 
         if (!pgpath) {
-                if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
+                if (must_push_back_bio(m))
                         return DM_MAPIO_REQUEUE;
                 dm_report_EIO(m);
                 return DM_MAPIO_KILL;
@@ -651,8 +683,7 @@ static int queue_if_no_path(struct multipath *m, bool queue_if_no_path,
         assign_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags,
                    (save_old_value && test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) ||
                    (!save_old_value && queue_if_no_path));
-        assign_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags,
-                   queue_if_no_path || dm_noflush_suspending(m->ti));
+        assign_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags, queue_if_no_path);
         spin_unlock_irqrestore(&m->lock, flags);
 
         if (!queue_if_no_path) {
@@ -1486,7 +1517,7 @@ static int multipath_end_io(struct dm_target *ti, struct request *clone,
                         fail_path(pgpath);
 
                 if (atomic_read(&m->nr_valid_paths) == 0 &&
-                    !test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
+                    !must_push_back_rq(m)) {
                         if (error == BLK_STS_IOERR)
                                 dm_report_EIO(m);
                         /* complete with the original error */
@@ -1521,8 +1552,12 @@ static int multipath_end_io_bio(struct dm_target *ti, struct bio *clone,
 
         if (atomic_read(&m->nr_valid_paths) == 0 &&
             !test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
-                dm_report_EIO(m);
-                *error = BLK_STS_IOERR;
+                if (must_push_back_bio(m)) {
+                        r = DM_ENDIO_REQUEUE;
+                } else {
+                        dm_report_EIO(m);
+                        *error = BLK_STS_IOERR;
+                }
                 goto done;
         }