xfs: hook live rmap operations during a repair operation

Hook the regular rmap code when an rmapbt repair operation is running so
that we can unlock the AGF buffer to scan the filesystem and keep the
in-memory btree up to date during the scan.

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

Author: Darrick J. Wong

fs/xfs/libxfs/xfs_ag.c

@@ -417,6 +417,7 @@ xfs_initialize_perag(
 		init_waitqueue_head(&pag->pag_active_wq);
 		pag->pagb_count = 0;
 		pag->pagb_tree = RB_ROOT;
+		xfs_hooks_init(&pag->pag_rmap_update_hooks);
 #endif /* __KERNEL__ */
 
 		error = xfs_buf_cache_init(&pag->pag_bcache);

fs/xfs/libxfs/xfs_ag.h

@@ -120,6 +120,9 @@ struct xfs_perag {
 	 * inconsistencies.
 	 */
 	struct xfs_defer_drain	pag_intents_drain;
+
+	/* Hook to feed rmapbt updates to an active online repair. */
+	struct xfs_hooks	pag_rmap_update_hooks;
 #endif /* __KERNEL__ */
 };
 

fs/xfs/libxfs/xfs_rmap.c

@@ -821,6 +821,86 @@ xfs_rmap_unmap(
 	return error;
 }
 
+#ifdef CONFIG_XFS_LIVE_HOOKS
+/*
+ * Use a static key here to reduce the overhead of rmapbt live updates.  If
+ * the compiler supports jump labels, the static branch will be replaced by a
+ * nop sled when there are no hook users.  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.
+ */
+DEFINE_STATIC_XFS_HOOK_SWITCH(xfs_rmap_hooks_switch);
+
+void
+xfs_rmap_hook_disable(void)
+{
+	xfs_hooks_switch_off(&xfs_rmap_hooks_switch);
+}
+
+void
+xfs_rmap_hook_enable(void)
+{
+	xfs_hooks_switch_on(&xfs_rmap_hooks_switch);
+}
+
+/* Call downstream hooks for a reverse mapping update. */
+static inline void
+xfs_rmap_update_hook(
+	struct xfs_trans		*tp,
+	struct xfs_perag		*pag,
+	enum xfs_rmap_intent_type	op,
+	xfs_agblock_t			startblock,
+	xfs_extlen_t			blockcount,
+	bool				unwritten,
+	const struct xfs_owner_info	*oinfo)
+{
+	if (xfs_hooks_switched_on(&xfs_rmap_hooks_switch)) {
+		struct xfs_rmap_update_params	p = {
+			.startblock	= startblock,
+			.blockcount	= blockcount,
+			.unwritten	= unwritten,
+			.oinfo		= *oinfo, /* struct copy */
+		};
+
+		if (pag)
+			xfs_hooks_call(&pag->pag_rmap_update_hooks, op, &p);
+	}
+}
+
+/* Call the specified function during a reverse mapping update. */
+int
+xfs_rmap_hook_add(
+	struct xfs_perag	*pag,
+	struct xfs_rmap_hook	*hook)
+{
+	return xfs_hooks_add(&pag->pag_rmap_update_hooks, &hook->rmap_hook);
+}
+
+/* Stop calling the specified function during a reverse mapping update. */
+void
+xfs_rmap_hook_del(
+	struct xfs_perag	*pag,
+	struct xfs_rmap_hook	*hook)
+{
+	xfs_hooks_del(&pag->pag_rmap_update_hooks, &hook->rmap_hook);
+}
+
+/* Configure rmap update hook functions. */
+void
+xfs_rmap_hook_setup(
+	struct xfs_rmap_hook	*hook,
+	notifier_fn_t		mod_fn)
+{
+	xfs_hook_setup(&hook->rmap_hook, mod_fn);
+}
+#else
+# define xfs_rmap_update_hook(t, p, o, s, b, u, oi)	do { } while (0)
+#endif /* CONFIG_XFS_LIVE_HOOKS */
+
 /*
  * Remove a reference to an extent in the rmap btree.
  */
@@ -841,7 +921,7 @@ xfs_rmap_free(
 		return 0;
 
 	cur = xfs_rmapbt_init_cursor(mp, tp, agbp, pag);
-
+	xfs_rmap_update_hook(tp, pag, XFS_RMAP_UNMAP, bno, len, false, oinfo);
 	error = xfs_rmap_unmap(cur, bno, len, false, oinfo);
 
 	xfs_btree_del_cursor(cur, error);
@@ -1093,6 +1173,7 @@ xfs_rmap_alloc(
 		return 0;
 
 	cur = xfs_rmapbt_init_cursor(mp, tp, agbp, pag);
+	xfs_rmap_update_hook(tp, pag, XFS_RMAP_MAP, bno, len, false, oinfo);
 	error = xfs_rmap_map(cur, bno, len, false, oinfo);
 
 	xfs_btree_del_cursor(cur, error);
@@ -2508,6 +2589,38 @@ xfs_rmap_finish_one_cleanup(
 		xfs_trans_brelse(tp, agbp);
 }
 
+/* Commit an rmap operation into the ondisk tree. */
+int
+__xfs_rmap_finish_intent(
+	struct xfs_btree_cur		*rcur,
+	enum xfs_rmap_intent_type	op,
+	xfs_agblock_t			bno,
+	xfs_extlen_t			len,
+	const struct xfs_owner_info	*oinfo,
+	bool				unwritten)
+{
+	switch (op) {
+	case XFS_RMAP_ALLOC:
+	case XFS_RMAP_MAP:
+		return xfs_rmap_map(rcur, bno, len, unwritten, oinfo);
+	case XFS_RMAP_MAP_SHARED:
+		return xfs_rmap_map_shared(rcur, bno, len, unwritten, oinfo);
+	case XFS_RMAP_FREE:
+	case XFS_RMAP_UNMAP:
+		return xfs_rmap_unmap(rcur, bno, len, unwritten, oinfo);
+	case XFS_RMAP_UNMAP_SHARED:
+		return xfs_rmap_unmap_shared(rcur, bno, len, unwritten, oinfo);
+	case XFS_RMAP_CONVERT:
+		return xfs_rmap_convert(rcur, bno, len, !unwritten, oinfo);
+	case XFS_RMAP_CONVERT_SHARED:
+		return xfs_rmap_convert_shared(rcur, bno, len, !unwritten,
+				oinfo);
+	default:
+		ASSERT(0);
+		return -EFSCORRUPTED;
+	}
+}
+
 /*
  * Process one of the deferred rmap operations.  We pass back the
  * btree cursor to maintain our lock on the rmapbt between calls.
@@ -2574,39 +2687,14 @@ xfs_rmap_finish_one(
 	unwritten = ri->ri_bmap.br_state == XFS_EXT_UNWRITTEN;
 	bno = XFS_FSB_TO_AGBNO(rcur->bc_mp, ri->ri_bmap.br_startblock);
 
-	switch (ri->ri_type) {
-	case XFS_RMAP_ALLOC:
-	case XFS_RMAP_MAP:
-		error = xfs_rmap_map(rcur, bno, ri->ri_bmap.br_blockcount,
-				unwritten, &oinfo);
-		break;
-	case XFS_RMAP_MAP_SHARED:
-		error = xfs_rmap_map_shared(rcur, bno,
-				ri->ri_bmap.br_blockcount, unwritten, &oinfo);
-		break;
-	case XFS_RMAP_FREE:
-	case XFS_RMAP_UNMAP:
-		error = xfs_rmap_unmap(rcur, bno, ri->ri_bmap.br_blockcount,
-				unwritten, &oinfo);
-		break;
-	case XFS_RMAP_UNMAP_SHARED:
-		error = xfs_rmap_unmap_shared(rcur, bno,
-				ri->ri_bmap.br_blockcount, unwritten, &oinfo);
-		break;
-	case XFS_RMAP_CONVERT:
-		error = xfs_rmap_convert(rcur, bno, ri->ri_bmap.br_blockcount,
-				!unwritten, &oinfo);
-		break;
-	case XFS_RMAP_CONVERT_SHARED:
-		error = xfs_rmap_convert_shared(rcur, bno,
-				ri->ri_bmap.br_blockcount, !unwritten, &oinfo);
-		break;
-	default:
-		ASSERT(0);
-		error = -EFSCORRUPTED;
-	}
+	error = __xfs_rmap_finish_intent(rcur, ri->ri_type, bno,
+			ri->ri_bmap.br_blockcount, &oinfo, unwritten);
+	if (error)
+		return error;
 
-	return error;
+	xfs_rmap_update_hook(tp, ri->ri_pag, ri->ri_type, bno,
+			ri->ri_bmap.br_blockcount, unwritten, &oinfo);
+	return 0;
 }
 
 /*

fs/xfs/libxfs/xfs_rmap.h

@@ -186,6 +186,10 @@ void xfs_rmap_finish_one_cleanup(struct xfs_trans *tp,
 		struct xfs_btree_cur *rcur, int error);
 int xfs_rmap_finish_one(struct xfs_trans *tp, struct xfs_rmap_intent *ri,
 		struct xfs_btree_cur **pcur);
+int __xfs_rmap_finish_intent(struct xfs_btree_cur *rcur,
+		enum xfs_rmap_intent_type op, xfs_agblock_t bno,
+		xfs_extlen_t len, const struct xfs_owner_info *oinfo,
+		bool unwritten);
 
 int xfs_rmap_lookup_le_range(struct xfs_btree_cur *cur, xfs_agblock_t bno,
 		uint64_t owner, uint64_t offset, unsigned int flags,
@@ -235,4 +239,29 @@ extern struct kmem_cache	*xfs_rmap_intent_cache;
 int __init xfs_rmap_intent_init_cache(void);
 void xfs_rmap_intent_destroy_cache(void);
 
+/*
+ * Parameters for tracking reverse mapping changes.  The hook function arg
+ * parameter is enum xfs_rmap_intent_type, and the rest is below.
+ */
+struct xfs_rmap_update_params {
+	xfs_agblock_t			startblock;
+	xfs_extlen_t			blockcount;
+	struct xfs_owner_info		oinfo;
+	bool				unwritten;
+};
+
+#ifdef CONFIG_XFS_LIVE_HOOKS
+
+struct xfs_rmap_hook {
+	struct xfs_hook			rmap_hook;
+};
+
+void xfs_rmap_hook_disable(void);
+void xfs_rmap_hook_enable(void);
+
+int xfs_rmap_hook_add(struct xfs_perag *pag, struct xfs_rmap_hook *hook);
+void xfs_rmap_hook_del(struct xfs_perag *pag, struct xfs_rmap_hook *hook);
+void xfs_rmap_hook_setup(struct xfs_rmap_hook *hook, notifier_fn_t mod_fn);
+#endif
+
 #endif	/* __XFS_RMAP_H__ */

fs/xfs/scrub/common.c

@@ -1309,6 +1309,9 @@ xchk_fsgates_enable(
 	if (scrub_fsgates & XCHK_FSGATES_DIRENTS)
 		xfs_dir_hook_enable();
 
+	if (scrub_fsgates & XCHK_FSGATES_RMAP)
+		xfs_rmap_hook_enable();
+
 	sc->flags |= scrub_fsgates;
 }
 

fs/xfs/scrub/repair.c

@@ -1165,3 +1165,39 @@ xrep_setup_xfbtree(
 
 	return xmbuf_alloc(sc->mp, descr, &sc->xmbtp);
 }
+
+/*
+ * Create a dummy transaction for use in a live update hook function.  This
+ * function MUST NOT be called from regular repair code because the current
+ * process' transaction is saved via the cookie.
+ */
+int
+xrep_trans_alloc_hook_dummy(
+	struct xfs_mount	*mp,
+	void			**cookiep,
+	struct xfs_trans	**tpp)
+{
+	int			error;
+
+	*cookiep = current->journal_info;
+	current->journal_info = NULL;
+
+	error = xfs_trans_alloc_empty(mp, tpp);
+	if (!error)
+		return 0;
+
+	current->journal_info = *cookiep;
+	*cookiep = NULL;
+	return error;
+}
+
+/* Cancel a dummy transaction used by a live update hook function. */
+void
+xrep_trans_cancel_hook_dummy(
+	void			**cookiep,
+	struct xfs_trans	*tp)
+{
+	xfs_trans_cancel(tp);
+	current->journal_info = *cookiep;
+	*cookiep = NULL;
+}

fs/xfs/scrub/repair.h

@@ -140,6 +140,10 @@ int xrep_quotacheck(struct xfs_scrub *sc);
 int xrep_reinit_pagf(struct xfs_scrub *sc);
 int xrep_reinit_pagi(struct xfs_scrub *sc);
 
+int xrep_trans_alloc_hook_dummy(struct xfs_mount *mp, void **cookiep,
+		struct xfs_trans **tpp);
+void xrep_trans_cancel_hook_dummy(void **cookiep, struct xfs_trans *tp);
+
 #else
 
 #define xrep_ino_dqattach(sc)	(0)