linux-ext4 - Re: [LTP] [PATCH] ext4: don't set SB

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Message-ID: <877canu0gr.fsf@mailhost.krisman.be>
Date: Fri, 04 Oct 2024 15:33:56 -0400
From: Gabriel Krisman Bertazi <gabriel@...sman.be>
To: Amir Goldstein <amir73il@...il.com>
Cc: Jan Kara <jack@...e.cz>,  Jan Stancek <jstancek@...hat.com>,  Christian
 Brauner <brauner@...nel.org>,  Ted Tso <tytso@....edu>,
  linux-fsdevel@...r.kernel.org,  linux-ext4@...r.kernel.org,
  ltp@...ts.linux.it,  Gabriel Krisman Bertazi <gabriel@...sman.be>
Subject: Re: [LTP] [PATCH] ext4: don't set SB_RDONLY after filesystem errors

Amir Goldstein <amir73il@...il.com> writes:

> On Mon, Sep 30, 2024 at 1:34 PM Jan Kara <jack@...e.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@...nel.org>
>> > > Signed-off-by: Jan Kara <jack@...e.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.

If I recall correctly, no, there is no need for the MS_RDONLY.  We only
care about getting the event to test FS_ERROR.

Thanks,

>
> Any objection for LTP maintainers to apply this simple test fix?
>
> 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");
>  }

-- 
Gabriel Krisman Bertazi