[PATCH] md/md-bitmap: bitmap pages leaked after recovery

[Nigel Croxon <ncroxon@redhat.com>]

The bitmap pages leaked after recovery if successful writes occur
concurrently during array degradation/recovery.

We performed write I/Os to an MD RAID1 array while it was in a degraded
state or actively undergoing recovery. Even after the array recovery
successfully reached 100%, the disk status returned to normal ([UU]),
and all I/Os completely stopped, the number of bitmap pages
(bitmap: n/N pages in /proc/mdstat) never dropped back to 0, resulting
in a persistent memory leak of bitmap pages.

Bitmap pages remain permanently allocated in the kernel memory even after
the array has fully returned to a healthy state, leading to a kernel
memory leak.

When a disk is re-added and recovery starts, MD_RECOVERY_RUNNING is set
in mddev->recovery.  The else if condition evaluates to false for normal
concurrent writes during recovery. NEEDED_MASK is never applied to these
blocks.

Fixes: 4f0e7d0e03b7
md/md-bitmap: remove the last parameter for bimtap_ops->endwrite()
This is becauses removing success caused bitmap_endwrite()
to treat mddev->degraded as a blanket trigger for NEEDED_MASK.

Signed-off-by: Nigel Croxon <ncroxon@redhat.com>
---
  drivers/md/md-bitmap.c | 9 ++++++++-
  1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 1d4a050dab3a..b8be0d079780 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -1756,7 +1756,14 @@ static void bitmap_end_write(struct mddev *mddev, 
sector_t offset,
                  sysfs_notify_dirent_safe(
                          bitmap->sysfs_can_clear);
              }
-        } else if (!NEEDED(*bmc)) {
+        /*
+         * Do not set NEEDED_MASK if recovery is actively running.
+         * Writes completing during recovery/resync are already covered by
+         * the recovery thread and setting NEEDED_MASK will cause orphaned
+         * bitmap flags and memory leaks after recovery finishes.
+         */
+        } else if (!test_bit(MD_RECOVERY_RUNNING,
+                &bitmap->mddev->recovery) && !NEEDED(*bmc)) {
              *bmc |= NEEDED_MASK;
          }

-- 
2.47.3