xfs: fix online repair probing when CONFIG_XFS_ONLINE_REPAIR=n

JIRA: https://issues.redhat.com/browse/RHEL-85590

commit 66314e9
Author: Darrick J. Wong <djwong@kernel.org>
Date:   Sun Feb 2 16:50:14 2025 -0800

    xfs: fix online repair probing when CONFIG_XFS_ONLINE_REPAIR=n

    I received a report from the release engineering side of the house that
    xfs_scrub without the -n flag (aka fix it mode) would try to fix a
    broken filesystem even on a kernel that doesn't have online repair built
    into it:

     # xfs_scrub -dTvn /mnt/test
     EXPERIMENTAL xfs_scrub program in use! Use at your own risk!
     Phase 1: Find filesystem geometry.
     /mnt/test: using 1 threads to scrub.
     Phase 1: Memory used: 132k/0k (108k/25k), time:  0.00/ 0.00/ 0.00s
     <snip>
     Phase 4: Repair filesystem.
     <snip>
     Info: /mnt/test/some/victimdir directory entries: Attempting repair. (repair.c line 351)
     Corruption: /mnt/test/some/victimdir directory entries: Repair unsuccessful; offline repair required. (repair.c line 204)

    Source: https://blogs.oracle.com/linux/post/xfs-online-filesystem-repair

    It is strange that xfs_scrub doesn't refuse to run, because the kernel
    is supposed to return EOPNOTSUPP if we actually needed to run a repair,
    and xfs_io's repair subcommand will perror that.  And yet:

     # xfs_io -x -c 'repair probe' /mnt/test
     #

    The first problem is commit dcb660f (4.15) which should have had
    xchk_probe set the CORRUPT OFLAG so that any of the repair machinery
    will get called at all.

    It turns out that some refactoring that happened in the 6.6-6.8 era
    broke the operation of this corner case.  What we *really* want to
    happen is that all the predicates that would steer xfs_scrub_metadata()
    towards calling xrep_attempt() should function the same way that they do
    when repair is compiled in; and then xrep_attempt gets to return the
    fatal EOPNOTSUPP error code that causes the probe to fail.

    Instead, commit 8336a64 (6.6) started the failwhale swimming by
    hoisting OFLAG checking logic into a helper whose non-repair stub always
    returns false, causing scrub to return "repair not needed" when in fact
    the repair is not supported.  Prior to that commit, the oflag checking
    that was open-coded in scrub.c worked correctly.

    Similarly, in commit 4bdfd7d (6.8) we hoisted the IFLAG_REPAIR
    and ALREADY_FIXED logic into a helper whose non-repair stub always
    returns false, so we never enter the if test body that would have called
    xrep_attempt, let alone fail to decode the OFLAGs correctly.

    The final insult (yes, we're doing The Naked Gun now) is commit
    48a72f6 (6.8) in which we hoisted the "are we going to try a
    repair?" predicate into yet another function with a non-repair stub
    always returns false.

    Fix xchk_probe to trigger xrep_probe if repair is enabled, or return
    EOPNOTSUPP directly if it is not.  For all the other scrub types, we
    need to fix the header predicates so that the ->repair functions (which
    are all xrep_notsupported) get called to return EOPNOTSUPP.  Commit
    48a72 is tagged here because the scrub code prior to LTS 6.12 are
    incomplete and not worth patching.

    Reported-by: David Flynn <david.flynn@oracle.com>
    Cc: <stable@vger.kernel.org> # v6.8
    Fixes: 8336a64 ("xfs: don't complain about unfixed metadata when repairs were injected")
    Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Carlos Maiolino <cem@kernel.org>

Signed-off-by: Bill O'Donnell <bodonnel@redhat.com>
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>

Author: cmaiolino

fs/xfs/scrub/common.h

@@ -179,7 +179,6 @@ static inline bool xchk_skip_xref(struct xfs_scrub_metadata *sm)
 bool xchk_dir_looks_zapped(struct xfs_inode *dp);
 bool xchk_pptr_looks_zapped(struct xfs_inode *ip);
 
-#ifdef CONFIG_XFS_ONLINE_REPAIR
 /* Decide if a repair is required. */
 static inline bool xchk_needs_repair(const struct xfs_scrub_metadata *sm)
 {
@@ -199,10 +198,6 @@ static inline bool xchk_could_repair(const struct xfs_scrub *sc)
 	return (sc->sm->sm_flags & XFS_SCRUB_IFLAG_REPAIR) &&
 		!(sc->flags & XREP_ALREADY_FIXED);
 }
-#else
-# define xchk_needs_repair(sc)		(false)
-# define xchk_could_repair(sc)		(false)
-#endif /* CONFIG_XFS_ONLINE_REPAIR */
 
 int xchk_metadata_inode_forks(struct xfs_scrub *sc);
 

fs/xfs/scrub/repair.h

@@ -163,7 +163,16 @@ bool xrep_buf_verify_struct(struct xfs_buf *bp, const struct xfs_buf_ops *ops);
 #else
 
 #define xrep_ino_dqattach(sc)	(0)
-#define xrep_will_attempt(sc)	(false)
+
+/*
+ * When online repair is not built into the kernel, we still want to attempt
+ * the repair so that the stub xrep_attempt below will return EOPNOTSUPP.
+ */
+static inline bool xrep_will_attempt(const struct xfs_scrub *sc)
+{
+	return (sc->sm->sm_flags & XFS_SCRUB_IFLAG_FORCE_REBUILD) ||
+		xchk_needs_repair(sc->sm);
+}
 
 static inline int
 xrep_attempt(

fs/xfs/scrub/scrub.c

@@ -149,6 +149,18 @@ xchk_probe(
 	if (xchk_should_terminate(sc, &error))
 		return error;
 
+	/*
+	 * If the caller is probing to see if repair works but repair isn't
+	 * built into the kernel, return EOPNOTSUPP because that's the signal
+	 * that userspace expects.  If online repair is built in, set the
+	 * CORRUPT flag (without any of the usual tracing/logging) to force us
+	 * into xrep_probe.
+	 */
+	if (xchk_could_repair(sc)) {
+		if (!IS_ENABLED(CONFIG_XFS_ONLINE_REPAIR))
+			return -EOPNOTSUPP;
+		sc->sm->sm_flags |= XFS_SCRUB_OFLAG_CORRUPT;
+	}
 	return 0;
 }