On Mon 05-08-24 22:12:41, Jan Kara wrote: > When the filesystem is mounted with errors=remount-ro, we were setting > SB_RDONLY flag to stop all filesystem modifications. We knew this misses > proper locking (sb->s_umount) and does not go through proper filesystem > remount procedure but it has been the way this worked since early ext2 > days and it was good enough for catastrophic situation damage > mitigation. Recently, syzbot has found a way (see link) to trigger > warnings in filesystem freezing because the code got confused by > SB_RDONLY changing under its hands. Since these days we set > EXT4_FLAGS_SHUTDOWN on the superblock which is enough to stop all > filesystem modifications, modifying SB_RDONLY shouldn't be needed. So > stop doing that. > > Link: https://lore.kernel.org/all/000000000000b90a8e061e21d12f@xxxxxxxxxx > Reported-by: Christian Brauner <brauner@xxxxxxxxxx> > Signed-off-by: Jan Kara <jack@xxxxxxx> > --- > fs/ext4/super.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > Note that this patch introduces fstests failure with generic/459 test > because it assumes that either freezing succeeds or 'ro' is among mount > options. But we fail the freeze with EFSCORRUPTED. This needs fixing in > the test but at this point I'm not sure how exactly. OK, I have noticed that recent versions of fstests have the check already improved and so generic/459 passes with these changes. Honza > > diff --git a/fs/ext4/super.c b/fs/ext4/super.c > index e72145c4ae5a..93c016b186c0 100644 > --- a/fs/ext4/super.c > +++ b/fs/ext4/super.c > @@ -735,11 +735,12 @@ static void ext4_handle_error(struct super_block *sb, bool force_ro, int error, > > ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only"); > /* > - * Make sure updated value of ->s_mount_flags will be visible before > - * ->s_flags update > + * EXT4_FLAGS_SHUTDOWN was set which stops all filesystem > + * modifications. We don't set SB_RDONLY because that requires > + * sb->s_umount semaphore and setting it without proper remount > + * procedure is confusing code such as freeze_super() leading to > + * deadlocks and other problems. > */ > - smp_wmb(); > - sb->s_flags |= SB_RDONLY; > } > > static void update_super_work(struct work_struct *work) > -- > 2.35.3 > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
