Petr Mladek d73b916bcc printk: Disable passing console lock owner completely during panic() ... [ Upstream commit d04d5882cd ] The commit d51507098f ("printk: disable optimistic spin during panic") added checks to avoid becoming a console waiter if a panic is in progress. However, the transition to panic can occur while there is already a waiter. The current owner should not pass the lock to the waiter because it might get stopped or blocked anytime. Also the panic context might pass the console lock owner to an already stopped waiter by mistake. It might happen when console_flush_on_panic() ignores the current lock owner, for example: CPU0 CPU1 ---- ---- console_lock_spinning_enable() console_trylock_spinning() [CPU1 now console waiter] NMI: panic() panic_other_cpus_shutdown() [stopped as console waiter] console_flush_on_panic() console_lock_spinning_enable() [print 1 record] console_lock_spinning_disable_and_check() [handover to stopped CPU1] This results in panic() not flushing the panic messages. Fix these problems by disabling all spinning operations completely during panic(). Another advantage is that it prevents possible deadlocks caused by "console_owner_lock". The panic() context does not need to take it any longer. The lockless checks are safe because the functions become NOPs when they see the panic in progress. All operations manipulating the state are still synchronized by the lock even when non-panic CPUs would notice the panic synchronously. The current owner might stay spinning. But non-panic() CPUs would get stopped anyway and the panic context will never start spinning. Fixes: dbdda842fe ("printk: Add console owner and waiter logic to load balance console writes") Signed-off-by: John Ogness <john.ogness@linutronix.de> Link: https://lore.kernel.org/r/20240207134103.1357162-12-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Sasha Levin <sashal@kernel.org>		2024-03-26 18:20:34 -04:00
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braille.c	printk: Replace strncmp() with str_has_prefix()	2019-08-16 09:54:08 +02:00
braille.h
console_cmdline.h	printk: Fix preferred console selection with multiple matches	2020-02-18 09:34:42 +01:00
index.c	kernel/printk/index.c: fix memory leak with using debugfs_lookup()	2023-03-11 13:55:32 +01:00
internal.h	Revert "printk: Wait for the global console lock when the system is going down"	2022-06-23 18:41:40 +02:00
Makefile	printk: move printk sysctl to printk/sysctl.c	2022-01-22 08:33:35 +02:00
printk.c	printk: Disable passing console lock owner completely during panic()	2024-03-26 18:20:34 -04:00
printk_ringbuffer.c	printk: ringbuffer: Fix truncating buffer size min_t cast	2023-09-13 09:43:00 +02:00
printk_ringbuffer.h	printk: ringbuffer: Improve prb_next_seq() performance	2022-01-26 16:00:32 +01:00
printk_safe.c	printk: Consolidate console deferred printing	2023-09-23 11:11:07 +02:00
sysctl.c	printk: Fix incorrect __user type in proc_dointvec_minmax_sysadmin()	2022-02-03 11:27:38 -08:00