Re: [LTP] [PATCH] ext4: don't set SB_RDONLY after filesystem errors

[Jan Stancek <jstancek@redhat.com>]

On Fri, Oct 4, 2024 at 2:32 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Mon, Sep 30, 2024 at 1:34 PM Jan Kara <jack@suse.cz> wrote:
> >
> > On Mon 30-09-24 12:15:11, Jan Stancek wrote:
> > > On Mon, Aug 05, 2024 at 10:12:41PM +0200, 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@google.com
> > > > Reported-by: Christian Brauner <brauner@kernel.org>
> > > > Signed-off-by: Jan Kara <jack@suse.cz>
> > > > ---
> > > > 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.
> > > >
> > > > 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;
> > >
> > > Hi,
> > >
> > > shouldn't the SB_RDONLY still be set (in __ext4_remount()) for the case
> > > when user triggers the abort with mount(.., "abort")? Because now we seem
> > > to always hit the condition that returns EROFS to user-space.
> >
> > Thanks for report! I agree returning EROFS from the mount although
> > 'aborting' succeeded is confusing and is mostly an unintended side effect
> > that after aborting the fs further changes to mount state are forbidden but
> > the testcase additionally wants to remount the fs read-only.
>
> Regardless of what is right or wrong to do in ext4, I don't think that the test
> really cares about remount read-only.
> I don't see anything in the test that requires it. Gabriel?
> If I remove MS_RDONLY from the test it works just fine.
>
> Any objection for LTP maintainers to apply this simple test fix?

Does that change work for you on older kernels? On 6.11 I get EROFS:

fanotify22.c:59: TINFO: Mounting /dev/loop0 to
/tmp/LTP_fangb5wuO/test_mnt fstyp=ext4 flags=20
fanotify22.c:59: TBROK: mount(/dev/loop0, test_mnt, ext4, 32,
0x4211ed) failed: EROFS (30)

>
> Thanks,
> Amir.
>
> --- a/testcases/kernel/syscalls/fanotify/fanotify22.c
> +++ b/testcases/kernel/syscalls/fanotify/fanotify22.c
> @@ -57,7 +57,7 @@ static struct fanotify_fid_t bad_link_fid;
>  static void trigger_fs_abort(void)
>  {
>         SAFE_MOUNT(tst_device->dev, MOUNT_PATH, tst_device->fs_type,
> -                  MS_REMOUNT|MS_RDONLY, "abort");
> +                  MS_REMOUNT, "abort");
>  }
>