17 files changed, 168 insertions, 5 deletions

diff --git a/fs/xfs/Kconfig b/fs/xfs/Kconfig
index ab24e683b440..05bc865142b8 100644
--- a/fs/xfs/Kconfig
+++ b/fs/xfs/Kconfig
@@ -95,6 +95,7 @@ config XFS_RT
 
 config XFS_DRAIN_INTENTS
 	bool
+	select JUMP_LABEL if HAVE_ARCH_JUMP_LABEL
 
 config XFS_ONLINE_SCRUB
 	bool "XFS online metadata check support"
diff --git a/fs/xfs/scrub/agheader.c b/fs/xfs/scrub/agheader.c
index c91819da1f5f..87cb13a6e84a 100644
--- a/fs/xfs/scrub/agheader.c
+++ b/fs/xfs/scrub/agheader.c
@@ -18,6 +18,15 @@
 #include "scrub/scrub.h"
 #include "scrub/common.h"
 
+int
+xchk_setup_agheader(
+	struct xfs_scrub	*sc)
+{
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
+	return xchk_setup_fs(sc);
+}
+
 /* Superblock */
 
 /* Cross-reference with the other btrees. */
diff --git a/fs/xfs/scrub/alloc.c b/fs/xfs/scrub/alloc.c
index 39e79b9536bc..de313df2b15b 100644
--- a/fs/xfs/scrub/alloc.c
+++ b/fs/xfs/scrub/alloc.c
@@ -24,6 +24,9 @@ int
 xchk_setup_ag_allocbt(
 	struct xfs_scrub	*sc)
 {
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
+
 	return xchk_setup_ag_btree(sc, false);
 }
 
diff --git a/fs/xfs/scrub/bmap.c b/fs/xfs/scrub/bmap.c
index f6d8cb938a02..a5078d63808f 100644
--- a/fs/xfs/scrub/bmap.c
+++ b/fs/xfs/scrub/bmap.c
@@ -31,6 +31,9 @@ xchk_setup_inode_bmap(
 {
 	int			error;
 
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
+
 	error = xchk_get_inode(sc);
 	if (error)
 		goto out;
diff --git a/fs/xfs/scrub/common.c b/fs/xfs/scrub/common.c
index 2a496d1699a3..87649facbbde 100644
--- a/fs/xfs/scrub/common.c
+++ b/fs/xfs/scrub/common.c
@@ -487,6 +487,8 @@ xchk_perag_drain_and_lock(
 			sa->agi_bp = NULL;
 		}
 
+		if (!(sc->flags & XCHK_FSGATES_DRAIN))
+			return -EDEADLOCK;
 		error = xfs_perag_intent_drain(sa->pag);
 		if (error == -ERESTARTSYS)
 			error = -EINTR;
@@ -1005,3 +1007,25 @@ xchk_start_reaping(
 	}
 	sc->flags &= ~XCHK_REAPING_DISABLED;
 }
+
+/*
+ * Enable filesystem hooks (i.e. runtime code patching) before starting a scrub
+ * operation.  Callers must not hold any locks that intersect with the CPU
+ * hotplug lock (e.g. writeback locks) because code patching must halt the CPUs
+ * to change kernel code.
+ */
+void
+xchk_fsgates_enable(
+	struct xfs_scrub	*sc,
+	unsigned int		scrub_fsgates)
+{
+	ASSERT(!(scrub_fsgates & ~XCHK_FSGATES_ALL));
+	ASSERT(!(sc->flags & scrub_fsgates));
+
+	trace_xchk_fsgates_enable(sc, scrub_fsgates);
+
+	if (scrub_fsgates & XCHK_FSGATES_DRAIN)
+		xfs_drain_wait_enable();
+
+	sc->flags |= scrub_fsgates;
+}
diff --git a/fs/xfs/scrub/common.h b/fs/xfs/scrub/common.h
index 273a4331da05..4714e8a43094 100644
--- a/fs/xfs/scrub/common.h
+++ b/fs/xfs/scrub/common.h
@@ -72,6 +72,7 @@ bool xchk_should_check_xref(struct xfs_scrub *sc, int *error,
 			   struct xfs_btree_cur **curpp);
 
 /* Setup functions */
+int xchk_setup_agheader(struct xfs_scrub *sc);
 int xchk_setup_fs(struct xfs_scrub *sc);
 int xchk_setup_ag_allocbt(struct xfs_scrub *sc);
 int xchk_setup_ag_iallocbt(struct xfs_scrub *sc);
@@ -151,4 +152,18 @@ int xchk_ilock_inverted(struct xfs_inode *ip, uint lock_mode);
 void xchk_stop_reaping(struct xfs_scrub *sc);
 void xchk_start_reaping(struct xfs_scrub *sc);
 
+/*
+ * Setting up a hook to wait for intents to drain is costly -- we have to take
+ * the CPU hotplug lock and force an i-cache flush on all CPUs once to set it
+ * up, and again to tear it down.  These costs add up quickly, so we only want
+ * to enable the drain waiter if the drain actually detected a conflict with
+ * running intent chains.
+ */
+static inline bool xchk_need_intent_drain(struct xfs_scrub *sc)
+{
+	return sc->flags & XCHK_TRY_HARDER;
+}
+
+void xchk_fsgates_enable(struct xfs_scrub *sc, unsigned int scrub_fshooks);
+
 #endif	/* __XFS_SCRUB_COMMON_H__ */
diff --git a/fs/xfs/scrub/fscounters.c b/fs/xfs/scrub/fscounters.c
index a38006c71bff..faa315be7978 100644
--- a/fs/xfs/scrub/fscounters.c
+++ b/fs/xfs/scrub/fscounters.c
@@ -130,6 +130,13 @@ xchk_setup_fscounters(
 	struct xchk_fscounters	*fsc;
 	int			error;
 
+	/*
+	 * If the AGF doesn't track btreeblks, we have to lock the AGF to count
+	 * btree block usage by walking the actual btrees.
+	 */
+	if (!xfs_has_lazysbcount(sc->mp))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
+
 	sc->buf = kzalloc(sizeof(struct xchk_fscounters), XCHK_GFP_FLAGS);
 	if (!sc->buf)
 		return -ENOMEM;
diff --git a/fs/xfs/scrub/ialloc.c b/fs/xfs/scrub/ialloc.c
index b14270bd1c62..9563769a8881 100644
--- a/fs/xfs/scrub/ialloc.c
+++ b/fs/xfs/scrub/ialloc.c
@@ -32,6 +32,8 @@ int
 xchk_setup_ag_iallocbt(
 	struct xfs_scrub	*sc)
 {
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
 	return xchk_setup_ag_btree(sc, sc->flags & XCHK_TRY_HARDER);
 }
 
diff --git a/fs/xfs/scrub/inode.c b/fs/xfs/scrub/inode.c
index dc66a1465f1b..bbf9432c02c2 100644
--- a/fs/xfs/scrub/inode.c
+++ b/fs/xfs/scrub/inode.c
@@ -32,6 +32,9 @@ xchk_setup_inode(
 {
 	int			error;
 
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
+
 	/*
 	 * Try to get the inode.  If the verifiers fail, we try again
 	 * in raw mode.
diff --git a/fs/xfs/scrub/quota.c b/fs/xfs/scrub/quota.c
index b019c70c065a..e6caa358cbda 100644
--- a/fs/xfs/scrub/quota.c
+++ b/fs/xfs/scrub/quota.c
@@ -53,6 +53,9 @@ xchk_setup_quota(
 	if (!xfs_this_quota_on(sc->mp, dqtype))
 		return -ENOENT;
 
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
+
 	error = xchk_setup_fs(sc);
 	if (error)
 		return error;
diff --git a/fs/xfs/scrub/refcount.c b/fs/xfs/scrub/refcount.c
index 756066f3dea2..6f649cc01310 100644
--- a/fs/xfs/scrub/refcount.c
+++ b/fs/xfs/scrub/refcount.c
@@ -27,6 +27,8 @@ int
 xchk_setup_ag_refcountbt(
 	struct xfs_scrub	*sc)
 {
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
 	return xchk_setup_ag_btree(sc, false);
 }
 
diff --git a/fs/xfs/scrub/rmap.c b/fs/xfs/scrub/rmap.c
index 4dc79e1a675d..c6e47ef4c79b 100644
--- a/fs/xfs/scrub/rmap.c
+++ b/fs/xfs/scrub/rmap.c
@@ -24,6 +24,9 @@ int
 xchk_setup_ag_rmapbt(
 	struct xfs_scrub	*sc)
 {
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
+
 	return xchk_setup_ag_btree(sc, false);
 }
 
diff --git a/fs/xfs/scrub/scrub.c b/fs/xfs/scrub/scrub.c
index 9364fe7d07b4..bd5d4357cd64 100644
--- a/fs/xfs/scrub/scrub.c
+++ b/fs/xfs/scrub/scrub.c
@@ -145,6 +145,21 @@ xchk_probe(
 
 /* Scrub setup and teardown */
 
+static inline void
+xchk_fsgates_disable(
+	struct xfs_scrub	*sc)
+{
+	if (!(sc->flags & XCHK_FSGATES_ALL))
+		return;
+
+	trace_xchk_fsgates_disable(sc, sc->flags & XCHK_FSGATES_ALL);
+
+	if (sc->flags & XCHK_FSGATES_DRAIN)
+		xfs_drain_wait_disable();
+
+	sc->flags &= ~XCHK_FSGATES_ALL;
+}
+
 /* Free all the resources and finish the transactions. */
 STATIC int
 xchk_teardown(
@@ -177,6 +192,8 @@ xchk_teardown(
 		kvfree(sc->buf);
 		sc->buf = NULL;
 	}
+
+	xchk_fsgates_disable(sc);
 	return error;
 }
 
@@ -191,25 +208,25 @@ static const struct xchk_meta_ops meta_scrub_ops[] = {
 	},
 	[XFS_SCRUB_TYPE_SB] = {		/* superblock */
 		.type	= ST_PERAG,
-		.setup	= xchk_setup_fs,
+		.setup	= xchk_setup_agheader,
 		.scrub	= xchk_superblock,
 		.repair	= xrep_superblock,
 	},
 	[XFS_SCRUB_TYPE_AGF] = {	/* agf */
 		.type	= ST_PERAG,
-		.setup	= xchk_setup_fs,
+		.setup	= xchk_setup_agheader,
 		.scrub	= xchk_agf,
 		.repair	= xrep_agf,
 	},
 	[XFS_SCRUB_TYPE_AGFL]= {	/* agfl */
 		.type	= ST_PERAG,
-		.setup	= xchk_setup_fs,
+		.setup	= xchk_setup_agheader,
 		.scrub	= xchk_agfl,
 		.repair	= xrep_agfl,
 	},
 	[XFS_SCRUB_TYPE_AGI] = {	/* agi */
 		.type	= ST_PERAG,
-		.setup	= xchk_setup_fs,
+		.setup	= xchk_setup_agheader,
 		.scrub	= xchk_agi,
 		.repair	= xrep_agi,
 	},
diff --git a/fs/xfs/scrub/scrub.h b/fs/xfs/scrub/scrub.h
index 72a5a8a64a87..4fdb6017f820 100644
--- a/fs/xfs/scrub/scrub.h
+++ b/fs/xfs/scrub/scrub.h
@@ -96,9 +96,18 @@ struct xfs_scrub {
 
 /* XCHK state flags grow up from zero, XREP state flags grown down from 2^31 */
 #define XCHK_TRY_HARDER		(1 << 0)  /* can't get resources, try again */
-#define XCHK_REAPING_DISABLED	(1 << 2)  /* background block reaping paused */
+#define XCHK_REAPING_DISABLED	(1 << 1)  /* background block reaping paused */
+#define XCHK_FSGATES_DRAIN	(1 << 2)  /* defer ops draining enabled */
 #define XREP_ALREADY_FIXED	(1 << 31) /* checking our repair work */
 
+/*
+ * The XCHK_FSGATES* flags reflect functionality in the main filesystem that
+ * are only enabled for this particular online fsck.  When not in use, the
+ * features are gated off via dynamic code patching, which is why the state
+ * must be enabled during scrub setup and can only be torn down afterwards.
+ */
+#define XCHK_FSGATES_ALL	(XCHK_FSGATES_DRAIN)
+
 /* Metadata scrubbers */
 int xchk_tester(struct xfs_scrub *sc);
 int xchk_superblock(struct xfs_scrub *sc);
diff --git a/fs/xfs/scrub/trace.h b/fs/xfs/scrub/trace.h
index ad25ae88fce1..304c55192c90 100644
--- a/fs/xfs/scrub/trace.h
+++ b/fs/xfs/scrub/trace.h
@@ -96,6 +96,12 @@ TRACE_DEFINE_ENUM(XFS_SCRUB_TYPE_FSCOUNTERS);
 	{ XFS_SCRUB_OFLAG_WARNING,		"warning" }, \
 	{ XFS_SCRUB_OFLAG_NO_REPAIR_NEEDED,	"norepair" }
 
+#define XFS_SCRUB_STATE_STRINGS \
+	{ XCHK_TRY_HARDER,			"try_harder" }, \
+	{ XCHK_REAPING_DISABLED,		"reaping_disabled" }, \
+	{ XCHK_FSGATES_DRAIN,			"fsgates_drain" }, \
+	{ XREP_ALREADY_FIXED,			"already_fixed" }
+
 DECLARE_EVENT_CLASS(xchk_class,
 	TP_PROTO(struct xfs_inode *ip, struct xfs_scrub_metadata *sm,
 		 int error),
@@ -142,6 +148,33 @@ DEFINE_SCRUB_EVENT(xchk_deadlock_retry);
 DEFINE_SCRUB_EVENT(xrep_attempt);
 DEFINE_SCRUB_EVENT(xrep_done);
 
+DECLARE_EVENT_CLASS(xchk_fsgate_class,
+	TP_PROTO(struct xfs_scrub *sc, unsigned int fsgate_flags),
+	TP_ARGS(sc, fsgate_flags),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(unsigned int, type)
+		__field(unsigned int, fsgate_flags)
+	),
+	TP_fast_assign(
+		__entry->dev = sc->mp->m_super->s_dev;
+		__entry->type = sc->sm->sm_type;
+		__entry->fsgate_flags = fsgate_flags;
+	),
+	TP_printk("dev %d:%d type %s fsgates '%s'",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  __print_symbolic(__entry->type, XFS_SCRUB_TYPE_STRINGS),
+		  __print_flags(__entry->fsgate_flags, "|", XFS_SCRUB_STATE_STRINGS))
+)
+
+#define DEFINE_SCRUB_FSHOOK_EVENT(name) \
+DEFINE_EVENT(xchk_fsgate_class, name, \
+	TP_PROTO(struct xfs_scrub *sc, unsigned int fsgates_flags), \
+	TP_ARGS(sc, fsgates_flags))
+
+DEFINE_SCRUB_FSHOOK_EVENT(xchk_fsgates_enable);
+DEFINE_SCRUB_FSHOOK_EVENT(xchk_fsgates_disable);
+
 TRACE_EVENT(xchk_op_error,
 	TP_PROTO(struct xfs_scrub *sc, xfs_agnumber_t agno,
 		 xfs_agblock_t bno, int error, void *ret_ip),
diff --git a/fs/xfs/xfs_drain.c b/fs/xfs/xfs_drain.c
index b431abdf0af1..005a66be44a2 100644
--- a/fs/xfs/xfs_drain.c
+++ b/fs/xfs/xfs_drain.c
@@ -12,6 +12,31 @@
 #include "xfs_ag.h"
 #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.
+ *
+ * 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);
+
+void
+xfs_drain_wait_disable(void)
+{
+	static_branch_dec(&xfs_drain_waiter_gate);
+}
+
+void
+xfs_drain_wait_enable(void)
+{
+	static_branch_inc(&xfs_drain_waiter_gate);
+}
+
 void
 xfs_defer_drain_init(
 	struct xfs_defer_drain	*dr)
@@ -46,6 +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) &&
 	    has_waiters(&dr->dr_waiters))
 		wake_up(&dr->dr_waiters);
 }
diff --git a/fs/xfs/xfs_drain.h b/fs/xfs/xfs_drain.h
index 9b16df3cc7dc..50a5772a8296 100644
--- a/fs/xfs/xfs_drain.h
+++ b/fs/xfs/xfs_drain.h
@@ -25,6 +25,9 @@ struct xfs_defer_drain {
 void xfs_defer_drain_init(struct xfs_defer_drain *dr);
 void xfs_defer_drain_free(struct xfs_defer_drain *dr);
 
+void xfs_drain_wait_disable(void);
+void xfs_drain_wait_enable(void);
+
 /*
  * Deferred Work Intent Drains
  * ===========================