Changing mount options always ends up taking lock_mount_hash() but when MNT_READONLY is requested and neither the mount nor the superblock are MNT_READONLY we end up taking the lock, dropping it, and retaking it to change the other mount attributes. Instead, let's acquire the lock once when changing the mount attributes. This simplifies the locking in these codepath, makes them easier to reason about and avoids having to reacquire the lock right after dropping it. Link: https://lore.kernel.org/r/20210112220124.837960-2-christian.brauner@xxxxxxxxxx Cc: David Howells <dhowells@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: linux-fsdevel@xxxxxxxxxxxxxxx Reviewed-by: Christoph Hellwig <hch@xxxxxx> Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx> --- /* v2 */ - Christoph Hellwig <hch@xxxxxx>: - Remove pointless __mnt_unmake_readonly() helper. - Even though Christoph suggested to lockdep_assert_held() into places that require {lock,unlock}_mount_hash() it seems that seqlock's don't support it. /* v3 */ unchanged /* v4 */ unchanged /* v5 */ unchanged base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837 /* v6 */ unchanged base-commit: 19c329f6808995b142b3966301f217c831e7cf31 --- fs/namespace.c | 22 ++++++++-------------- 1 file changed, 8 insertions(+), 14 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index ecdc63ef881c..bdfb130f2c3c 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -464,7 +464,6 @@ static int mnt_make_readonly(struct mount *mnt) { int ret = 0; - lock_mount_hash(); mnt->mnt.mnt_flags |= MNT_WRITE_HOLD; /* * After storing MNT_WRITE_HOLD, we'll read the counters. This store @@ -498,18 +497,9 @@ static int mnt_make_readonly(struct mount *mnt) */ smp_wmb(); mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD; - unlock_mount_hash(); return ret; } -static int __mnt_unmake_readonly(struct mount *mnt) -{ - lock_mount_hash(); - mnt->mnt.mnt_flags &= ~MNT_READONLY; - unlock_mount_hash(); - return 0; -} - int sb_prepare_remount_readonly(struct super_block *sb) { struct mount *mnt; @@ -2523,7 +2513,8 @@ static int change_mount_ro_state(struct mount *mnt, unsigned int mnt_flags) if (readonly_request) return mnt_make_readonly(mnt); - return __mnt_unmake_readonly(mnt); + mnt->mnt.mnt_flags &= ~MNT_READONLY; + return 0; } /* @@ -2532,11 +2523,9 @@ static int change_mount_ro_state(struct mount *mnt, unsigned int mnt_flags) */ static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags) { - lock_mount_hash(); mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK; mnt->mnt.mnt_flags = mnt_flags; touch_mnt_namespace(mnt->mnt_ns); - unlock_mount_hash(); } static void mnt_warn_timestamp_expiry(struct path *mountpoint, struct vfsmount *mnt) @@ -2582,9 +2571,11 @@ static int do_reconfigure_mnt(struct path *path, unsigned int mnt_flags) return -EPERM; down_write(&sb->s_umount); + lock_mount_hash(); ret = change_mount_ro_state(mnt, mnt_flags); if (ret == 0) set_mount_attributes(mnt, mnt_flags); + unlock_mount_hash(); up_write(&sb->s_umount); mnt_warn_timestamp_expiry(path, &mnt->mnt); @@ -2625,8 +2616,11 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags, err = -EPERM; if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) { err = reconfigure_super(fc); - if (!err) + if (!err) { + lock_mount_hash(); set_mount_attributes(mnt, mnt_flags); + unlock_mount_hash(); + } } up_write(&sb->s_umount); } -- 2.30.0
