From 66644b992f25f6a33775788c8b69a8bb3d41ad67 Mon Sep 17 00:00:00 2001 From: Edward Adam Davis Date: Tue, 20 Oct 2026 09:05:59 +0800 Subject: [PATCH] kernel/reboot: avoid potential deadlocks during suspension Invoking reboot with LINUX_REBOOT_CMD_SW_SUSPEND causes kernel/reboot.c to acquire system_transition_mutex and invoke hibernate(). hibernate() calls lock_system_sleep(), which sets PF_NOFREEZE on current and attempts to acquire system_transition_mutex again, potentially hitting: WARNING: possible recursive locking detected -------------------------------------------- syz.3.5755/5950 is trying to acquire lock: ffffffff8fc04760 (system_transition_mutex){+.+.}-{4:4}, at: lock_system_sleep+0x49/0x70 kernel/power/main.c:71 but task is already holding lock: ffffffff8fc04760 (system_transition_mutex){+.+.}-{4:4}, at: __do_sys_reboot kernel/reboot.c:774 [inline] ffffffff8fc04760 (system_transition_mutex){+.+.}-{4:4}, at: __se_sys_reboot+0x223/0x460 kernel/reboot.c:738 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(system_transition_mutex); lock(system_transition_mutex); *** DEADLOCK *** May be due to missing lock nesting notation locks held by syz.3.5755/5950: 1, last CPU#0: #0: ffffffff8fc04760 (system_transition_mutex){+.+.}-{4:4}, at: __do_sys_reboot kernel/reboot.c:774 [inline] #0: ffffffff8fc04760 (system_transition_mutex){+.+.}-{4:4}, at: __se_sys_reboot+0x223/0x460 kernel/reboot.c:738 Call Trace: lock_system_sleep+0x49/0x70 kernel/power/main.c:71 hibernate+0x162/0x680 kernel/power/hibernate.c:784 __do_sys_reboot kernel/reboot.c:816 [inline] Move the suspension operation outside the scope protected by lock system_transition_mutex. Link: https://lore.kernel.org/20261020010559.23031-1-eadavis@sina.com Fixes: 55f2503c3b69 ("PM / reboot: Eliminate race between reboot and suspend") Signed-off-by: Edward Adam Davis Signed-off-by: Andrew Morton Reported-by: Closes: https://syzkaller.appspot.com/bug?extid=1f0fbc2561b3e5d51b91 Tested-by: Reviewed-by: Bradley Morgan Cc: Pingfan Liu Cc: "Rafael J. Wysocki" --- kernel/reboot.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/reboot.c b/kernel/reboot.c index d177d89fcc33..77c1521cf32b 100644 --- a/kernel/reboot.c +++ b/kernel/reboot.c @@ -804,8 +804,8 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd, #ifdef CONFIG_HIBERNATION case LINUX_REBOOT_CMD_SW_SUSPEND: - ret = hibernate(); - break; + mutex_unlock(&system_transition_mutex); + return hibernate(); #endif default: