[Cluster-devel] [PATCH] gfs2: Flag a withdraw if init_threads() fails

[Andreas Gruenbacher <agruenba@redhat.com>]

On Mon, Mar 15, 2021 at 1:24 PM Andrew Price <anprice@redhat.com> wrote:
> Interrupting mount with ^C quickly enough can cause the kthread_run()
> calls in gfs2's init_threads() to fail and the error path leads to a
> deadlock on the s_umount rwsem. The abridged chain of events is:
>
>   [mount path]
>   get_tree_bdev()
>     sget_fc()
>       alloc_super()
>         down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING); [acquired]
>     gfs2_fill_super()
>       gfs2_make_fs_rw()
>         init_threads()
>           kthread_run()
>             ( Interrupted )
>       [Error path]
>       gfs2_gl_hash_clear()
>         flush_workqueue(glock_workqueue)
>           wait_for_completion()
>
>   [workqueue context]
>   glock_work_func()
>     run_queue()
>       do_xmote()
>         freeze_go_sync()
>           freeze_super()
>             down_write(&sb->s_umount) [deadlock]
>
> In freeze_go_sync() there is a gfs2_withdrawn() check that we can use to
> make sure freeze_super() is not called in the error path, so add a
> gfs2_withdraw_delayed() call when init_threads() fails.
>
> Ref: https://bugzilla.kernel.org/show_bug.cgi?id=212231
>
> Reported-by: Alexander Aring <aahringo@redhat.com>
> Signed-off-by: Andrew Price <anprice@redhat.com>
> ---
>  fs/gfs2/super.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
> index 97076d3f562f..9e91c9d92bd6 100644
> --- a/fs/gfs2/super.c
> +++ b/fs/gfs2/super.c
> @@ -162,8 +162,10 @@ int gfs2_make_fs_rw(struct gfs2_sbd *sdp)
>         int error;
>
>         error = init_threads(sdp);
> -       if (error)
> +       if (error) {
> +               gfs2_withdraw_delayed(sdp);

Hmm, marking the filesystem as withdrawing before we've even started
looks a bit odd, but given that we're already checking for withdrawing
/ withdrawn filesystems all over the place, it should be okay. I'll
push this to for-next.

>                 return error;
> +       }
>
>         j_gl->gl_ops->go_inval(j_gl, DIO_METADATA);
>         if (gfs2_withdrawn(sdp)) {
> --
> 2.29.2

Thanks,
Andreas