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

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Message-ID: <CAOQ4uxjXE7Tyz39wLUcuSTijy37vgUjYxvGL21E32cxStAgQpQ@mail.gmail.com>
Date: Fri, 4 Oct 2024 14:32:07 +0200
From: Amir Goldstein <amir73il@...il.com>
To: Jan Kara <jack@...e.cz>
Cc: 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

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.

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");
 }