FAILED: patch "[PATCH] xfs: read only mounts with fsopen mount API are busted" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x d8d222e09dab84a17bb65dda4b94d01c565f5327
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024012736-provable-risotto-2228@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d8d222e09dab84a17bb65dda4b94d01c565f5327 Mon Sep 17 00:00:00 2001
From: Dave Chinner <[email protected]>
Date: Tue, 16 Jan 2024 15:33:07 +1100
Subject: [PATCH] xfs: read only mounts with fsopen mount API are busted

Recently xfs/513 started failing on my test machines testing "-o ro,norecovery" mount options. This was being emitted in dmesg:

[ 9906.932724] XFS (pmem0): no-recovery mounts must be read-only.

Turns out, readonly mounts with the fsopen()/fsconfig() mount API have been busted since day zero. It's only taken 5 years for debian unstable to start using this "new" mount API, and shortly after this I noticed xfs/513 had started to fail as per above.

The syscall trace is:

fsopen("xfs", FSOPEN_CLOEXEC) = 3
mount_setattr(-1, NULL, 0, NULL, 0) = -1 EINVAL (Invalid argument)
.....
fsconfig(3, FSCONFIG_SET_STRING, "source", "/dev/pmem0", 0) = 0 fsconfig(3, FSCONFIG_SET_FLAG, "ro", NULL, 0) = 0
fsconfig(3, FSCONFIG_SET_FLAG, "norecovery", NULL, 0) = 0 fsconfig(3, FSCONFIG_CMD_CREATE, NULL, NULL, 0) = -1 EINVAL (Invalid argument)
close(3) = 0

Showing that the actual mount instantiation (FSCONFIG_CMD_CREATE) is what threw out the error.

During mount instantiation, we call xfs_fs_validate_params() which does:

        /* No recovery flag requires a read-only mount */
        if (xfs_has_norecovery(mp) && !xfs_is_readonly(mp)) {
                xfs_warn(mp, "no-recovery mounts must be read-only.");
                return -EINVAL;
        }

and xfs_is_readonly() checks internal mount flags for read only state. This state is set in xfs_init_fs_context() from the context superblock flag state:

        /*
         * Copy binary VFS mount flags we are interested in.
         */
        if (fc->sb_flags & SB_RDONLY)
                set_bit(XFS_OPSTATE_READONLY, &mp->m_opstate);

With the old mount API, all of the VFS specific superblock flags had already been parsed and set before xfs_init_fs_context() is called, so this all works fine.

However, in the brave new fsopen/fsconfig world, xfs_init_fs_context() is called from fsopen() context, before any VFS superblock have been set or parsed. Hence if we use fsopen(), the internal XFS readonly state is *never set*. Hence anything that depends on xfs_is_readonly() actually returning true for read only mounts is broken if fsopen() has been used to mount the filesystem.

Fix this by moving this internal state initialisation to xfs_fs_fill_super() before we attempt to validate the parameters that have been set prior to the FSCONFIG_CMD_CREATE call being made.

index aff20ddd4a9f..5a2512d20bd0 100644
@@ -1496,6 +1496,18 @@ xfs_fs_fill_super(
 
 	mp->m_super = sb;
 
+	/*
+	 * Copy VFS mount flags from the context now that all parameter parsing
+	 * is guaranteed to have been completed by either the old mount API or
+	 * the newer fsopen/fsconfig API.
+	 */
+	if (fc->sb_flags & SB_RDONLY)
+		set_bit(XFS_OPSTATE_READONLY, &mp->m_opstate);
+	if (fc->sb_flags & SB_DIRSYNC)
+		mp->m_features |= XFS_FEAT_DIRSYNC;
+	if (fc->sb_flags & SB_SYNCHRONOUS)
+		mp->m_features |= XFS_FEAT_WSYNC;
+
 	error = xfs_fs_validate_params(mp);
 	if (error)
 		return error;

@@ -1965,6 +1977,11 @@ static const struct fs_context_operations xfs_context_ops = {
 	.free        = xfs_fs_free,
 };
 
+/*
+ * WARNING: do not initialise any parameters in this function that depend on
+ * mount option parsing having already been performed as this can be called from
+ * fsopen() before any parameters have been set.
+ */
 static int xfs_init_fs_context(
 	struct fs_context	*fc)
 {

@@ -1996,16 +2013,6 @@ static int xfs_init_fs_context(
 	mp->m_logbsize = -1;
 	mp->m_allocsize_log = 16; /* 64k */
 
-	/*
-	 * Copy binary VFS mount flags we are interested in.
-	 */
-	if (fc->sb_flags & SB_RDONLY)
-		set_bit(XFS_OPSTATE_READONLY, &mp->m_opstate);
-	if (fc->sb_flags & SB_DIRSYNC)
-		mp->m_features |= XFS_FEAT_DIRSYNC;
-	if (fc->sb_flags & SB_SYNCHRONOUS)
-		mp->m_features |= XFS_FEAT_WSYNC;
-
 	fc->s_fs_info = mp;
 	fc->ops = &xfs_context_ops;