xfs: allow queued realtime intents to drain before scrubbing

When a writer thread executes a chain of log intent items for the
realtime volume, the ILOCKs taken during each step are for each rt
metadata file, not the entire rt volume itself.  Although scrub takes
all rt metadata ILOCKs, this isn't sufficient to guard against scrub
checking the rt volume while that writer thread is in the middle of
finishing a chain because there's no higher level locking primitive
guarding the realtime volume.

When there's a collision, cross-referencing between data structures
(e.g. rtrmapbt and rtrefcountbt) yields false corruption events; if
repair is running, this results in incorrect repairs, which is
catastrophic.

Fix this by adding to the mount structure the same drain that we use to
protect scrub against concurrent AG updates, but this time for the
realtime volume.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 10 insertions, 10 deletions

diff --git a/fs/xfs/xfs_drain.c b/fs/xfs/xfs_drain.c
index 5ede81fadbd8..fa5f31931efd 100644
--- a/fs/xfs/xfs_drain.c
+++ b/fs/xfs/xfs_drain.c
@@ -13,28 +13,28 @@
 #include "xfs_trace.h"
 
 /*
- * Use a static key here to reduce the overhead of xfs_drain_rele.  If the
- * compiler supports jump labels, the static branch will be replaced by a nop
- * sled when there are no xfs_drain_wait callers.  Online fsck is currently
- * the only caller, so this is a reasonable tradeoff.
+ * Use a static key here to reduce the overhead of xfs_defer_drain_rele.  If
+ * the compiler supports jump labels, the static branch will be replaced by a
+ * nop sled when there are no xfs_defer_drain_wait callers.  Online fsck is
+ * currently the only caller, so this is a reasonable tradeoff.
  *
  * Note: Patching the kernel code requires taking the cpu hotplug lock.  Other
  * parts of the kernel allocate memory with that lock held, which means that
  * XFS callers cannot hold any locks that might be used by memory reclaim or
  * writeback when calling the static_branch_{inc,dec} functions.
  */
-static DEFINE_STATIC_KEY_FALSE(xfs_drain_waiter_gate);
+static DEFINE_STATIC_KEY_FALSE(xfs_defer_drain_waiter_gate);
 
 void
-xfs_drain_wait_disable(void)
+xfs_defer_drain_wait_disable(void)
 {
-	static_branch_dec(&xfs_drain_waiter_gate);
+	static_branch_dec(&xfs_defer_drain_waiter_gate);
 }
 
 void
-xfs_drain_wait_enable(void)
+xfs_defer_drain_wait_enable(void)
 {
-	static_branch_inc(&xfs_drain_waiter_gate);
+	static_branch_inc(&xfs_defer_drain_waiter_gate);
 }
 
 void
@@ -71,7 +71,7 @@ static inline bool has_waiters(struct wait_queue_head *wq_head)
 static inline void xfs_defer_drain_rele(struct xfs_defer_drain *dr)
 {
 	if (atomic_dec_and_test(&dr->dr_count) &&
-	    static_branch_unlikely(&xfs_drain_waiter_gate) &&
+	    static_branch_unlikely(&xfs_defer_drain_waiter_gate) &&
 	    has_waiters(&dr->dr_waiters))
 		wake_up(&dr->dr_waiters);
 }