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charset=us-ascii Content-Disposition: inline In-Reply-To: <20240803081230.223512-1-takakura@valinux.co.jp> On Sat 2024-08-03 17:12:30, takakura@valinux.co.jp wrote: > From: Ryo Takakura > > After panic, non-panicked CPU's has been unable to flush ringbuffer > while they can still write into it. This can affect CPU backtrace > triggered in panic only able to write into ringbuffer incapable of > flushing them. > > Fix the issue by letting the panicked CPU handle the flushing of > ringbuffer right after non-panicked CPUs finished writing their > backtraces. > > Signed-off-by: Ryo Takakura > --- > kernel/panic.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/panic.c b/kernel/panic.c > index 7e2070925..f94923a63 100644 > --- a/kernel/panic.c > +++ b/kernel/panic.c > @@ -252,8 +252,10 @@ void check_panic_on_warn(const char *origin) > */ > static void panic_other_cpus_shutdown(bool crash_kexec) > { > - if (panic_print & PANIC_PRINT_ALL_CPU_BT) > + if (panic_print & PANIC_PRINT_ALL_CPU_BT) { > trigger_all_cpu_backtrace(); > + console_flush_on_panic(CONSOLE_FLUSH_PENDING); Hmm, this is too dangerous. console_flush_on_panic() is supposed to be called at the end on panic() as the final desperate attempt to flush consoles. It does not take console_lock(). It must not be called before stopping non-panic() CPUs. We would need to implement something like: /** * console_try_flush - try to flush consoles when safe * * Context: Any, except for NMI. */ void console_try_flush(void) { if (is_printk_legacy_deferred()) return; if (console_trylock()) console_unlock(); } , where is_printk_legacy_deferred() is not yet in the mainline. It is a new API proposed by the last version of a patchset adding adding write_atomic() callback, see https://lore.kernel.org/all/20240804005138.3722656-24-john.ogness@linutronix.de/ Best Regards, Petr