From 445c31ac638fd1af203d79bdf25fc0cb3149fbbc Mon Sep 17 00:00:00 2001 From: Peter Oberparleiter Date: Wed, 12 Aug 2026 09:53:19 +0200 Subject: [PATCH] s390/debug: Fix deadlock during unregister 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. Fixes: 9372a82892c2 ("s390/debug: fix debug area life cycle") Signed-off-by: Peter Oberparleiter Reviewed-by: Heiko Carstens Signed-off-by: Vasily Gorbik --- arch/s390/kernel/debug.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c index dbf430f479bd..14d2b58ad093 100644 --- a/arch/s390/kernel/debug.c +++ b/arch/s390/kernel/debug.c @@ -993,8 +993,8 @@ void debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas) mutex_unlock(&debug_mutex); } -/* Remove debugfs entries and remove from internal list. */ -static void _debug_unregister(debug_info_t *id) +/* Remove debugfs entries. */ +static void _debug_unregister_debugfs(debug_info_t *id) { int i; @@ -1004,6 +1004,11 @@ static void _debug_unregister(debug_info_t *id) debugfs_remove(id->debugfs_entries[i]); } debugfs_remove(id->debugfs_root_entry); +} + +/* Remove from internal list. */ +static void _debug_unregister(debug_info_t *id) +{ if (id == debug_area_first) debug_area_first = id->next; if (id == debug_area_last) @@ -1029,6 +1034,7 @@ void debug_unregister(debug_info_t *id) mutex_lock(&debug_mutex); _debug_unregister(id); mutex_unlock(&debug_mutex); + _debug_unregister_debugfs(id); debug_info_put(id); }