[PATCH v3 32/33] ext4: use the generic emergency read-only state

[Christian Brauner <brauner@kernel.org>]

Set SB_STATE_EMERGENCY_RO next to EXT4_FLAGS_EMERGENCY_RO when an error
makes the filesystem read-only. The VFS then refuses modifications
before they reach ext4 and reports the superblock as read-only like it
did when ext4 still set SB_RDONLY. The shutdown state stays ext4's own
and so do all of ext4's checks because they cover both states. ext4
keeps showing "emergency_ro" in its mount options.

EXT4_IOC_SHUTDOWN with EXT4_GOING_FLAGS_DEFAULT fails after an error on
mainline today because ext4_sync_fs() fails the freeze. freeze_super()
refuses it in the emergency state now. ext4 refuses writes in that state
anyway and the journal is aborted, so shut down without the freeze like
EXT4_GOING_FLAGS_NOLOGFLUSH does.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/ext4/ioctl.c | 4 ++++
 fs/ext4/super.c | 1 +
 2 files changed, 5 insertions(+)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index e8e579498c990..ce0e0ebdded61 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -821,6 +821,10 @@ int ext4_force_shutdown(struct super_block *sb, u32 flags)
 	ext4_msg(sb, KERN_ALERT, "shut down requested (%d)", flags);
 	trace_ext4_shutdown(sb, flags);
 
+	/* After an error there is nothing to flush and freezing fails. */
+	if (flags == EXT4_GOING_FLAGS_DEFAULT && ext4_emergency_ro(sb))
+		flags = EXT4_GOING_FLAGS_NOLOGFLUSH;
+
 	switch (flags) {
 	case EXT4_GOING_FLAGS_DEFAULT:
 		ret = bdev_freeze(sb->s_bdev);
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index ae5ba6823c01c..afbdbb607b144 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -757,6 +757,7 @@ static void ext4_handle_error(struct super_block *sb, bool force_ro, int error,
 	 * and other problems.
 	 */
 	set_bit(EXT4_FLAGS_EMERGENCY_RO, &EXT4_SB(sb)->s_ext4_flags);
+	sb_set_emergency_ro(sb);
 }
 
 static void update_super_work(struct work_struct *work)

-- 
2.53.0


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