On Mon, Sep 30, 2024 at 1:34 PM Jan Kara <jack@xxxxxxx> 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@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. > > > > > > 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"); }
