Re: [PATCH] s390/debug: Fix deadlock during unregister

On Wed, Aug 12, 2026 at 09:53:19AM +0200, Peter Oberparleiter wrote:
> Unregistering an s390dbf debug area while one of the associated debugfs
> files is being written to can cause a deadlock:
> 
> $ echo >.../vmur/level    $ rmmod vmur
> ===================================================
> debugfs write
> debugfs_file_get()
>                           debug_unregister()
>                           mutex_lock(debug_mutex)
>                           debugfs_remove()
>                           wait for debugfs_file_put()
> debug_file_ops.write()
> debug_input()
> mutex_lock(debug_mutex) ==> DEADLOCK
> 
> Fix this by splitting debug_unregister() into an s390dbf and debugfs
> part, and running only the s390dbf part with debug_mutex locked.
> 
> Signed-off-by: Peter Oberparleiter <[email protected]>
> ---
>  arch/s390/kernel/debug.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)

Reviewed-by: Heiko Carstens <[email protected]>