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Groups > linux.kernel > #1615809
| From | Petr Mladek <pmladek@suse.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [RFC][PATCHv2 2/8] printk: introduce printing kernel thread |
| Date | 2017-04-04 11:10 +0200 |
| Message-ID | <tssDo-2Qa-25@gated-at.bofh.it> (permalink) |
| References | <tqi5s-4RU-3@gated-at.bofh.it> <tqi5s-4RU-15@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Wed 2017-03-29 18:25:05, Sergey Senozhatsky wrote:
> This patch introduces a dedicated printing kernel thread - printk_kthread.
> The main purpose of this kthread is to offload printing to a non-atomic
> and always scheduleable context, which eliminates 4) and makes 1)-3) less
> critical. printk() now just appends log messages to the kernel log buffer
> and wake_up()s printk_kthread instead of locking console_sem and calling
> into potentially unsafe console_unlock().
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 2d07678e9ff9..ab6b3b2a68c6 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -445,6 +447,42 @@ static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
> static char *log_buf = __log_buf;
> static u32 log_buf_len = __LOG_BUF_LEN;
>
> +static struct task_struct *printk_kthread __read_mostly;
> +/*
> + * We can't call into the scheduler (wake_up() printk kthread) during
> + * suspend/kexec/etc. This temporarily switches printk to old behaviour.
> + */
> +static atomic_t printk_emergency __read_mostly;
> +/*
> + * Disable printk_kthread permanently. Unlike `oops_in_progress'
> + * it doesn't go back to 0.
> + */
The comment is not valid once we allow to modify the variable using
the sysfs knob.
> @@ -1765,17 +1803,40 @@ asmlinkage int vprintk_emit(int facility, int level,
>
> printed_len += log_output(facility, level, lflags, dict, dictlen, text, text_len);
>
> + /*
> + * Emergency level indicates that the system is unstable and, thus,
> + * we better stop relying on wake_up(printk_kthread) and try to do
> + * a direct printing.
> + */
> + if (level == LOGLEVEL_EMERG)
> + printk_kthread_disabled = true;
> +
> + set_bit(PRINTK_PENDING_OUTPUT, &printk_pending);
> logbuf_unlock_irqrestore(flags);
>
> /* If called from the scheduler, we can not call up(). */
> if (!in_sched) {
> /*
> - * Try to acquire and then immediately release the console
> - * semaphore. The release will print out buffers and wake up
> - * /dev/kmsg and syslog() users.
> + * Under heavy printing load/slow serial console/etc
> + * console_unlock() can stall CPUs, which can result in
> + * soft/hard-lockups, lost interrupts, RCU stalls, etc.
> + * Therefore we attempt to print the messages to console
> + * from a dedicated printk_kthread, which always runs in
> + * schedulable context.
> */
> - if (console_trylock())
> - console_unlock();
> + if (printk_kthread_enabled()) {
> + printk_safe_enter_irqsave(flags);
> + wake_up_process(printk_kthread);
> + printk_safe_exit_irqrestore(flags);
I am really happy that we have the printk_safe stuff available!
> + } else {
> + /*
> + * Try to acquire and then immediately release the
> + * console semaphore. The release will print out
> + * buffers and wake up /dev/kmsg and syslog() users.
> + */
> + if (console_trylock())
> + console_unlock();
> + }
> }
>
> return printed_len;
> @@ -1882,6 +1943,9 @@ static size_t msg_print_text(const struct printk_log *msg,
> bool syslog, char *buf, size_t size) { return 0; }
> static bool suppress_message_printing(int level) { return false; }
>
> +void printk_emergency_begin(void) {}
> +void printk_emergency_end(void) {}
> +
> #endif /* CONFIG_PRINTK */
>
> #ifdef CONFIG_EARLY_PRINTK
> @@ -2164,6 +2228,13 @@ void console_unlock(void)
> bool do_cond_resched, retry;
>
> if (console_suspended) {
> + /*
> + * Avoid an infinite loop in printk_kthread function
> + * when console_unlock() cannot flush messages because
> + * we suspended consoles. Someone else will print the
> + * messages from resume_console().
> + */
> + clear_bit(PRINTK_PENDING_OUTPUT, &printk_pending);
Great catch!
> up_console_sem();
> return;
> }
> @@ -2182,6 +2253,7 @@ void console_unlock(void)
> console_may_schedule = 0;
>
> again:
> + clear_bit(PRINTK_PENDING_OUTPUT, &printk_pending);
This will not help if new messages appear during
call_console_drivers().
I would move this line after the for(;;) cycle. It will be
cleared when all messages are really handled.
Otherwise, it looks fine to me.
Best Regards,
Petr
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
[RFC][PATCHv2 0/8] printk: introduce printing kernel thread Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-03-29 11:30 +0200
[RFC][PATCHv2 2/8] printk: introduce printing kernel thread Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-03-29 11:30 +0200
Re: [RFC][PATCHv2 2/8] printk: introduce printing kernel thread Petr Mladek <pmladek@suse.com> - 2017-04-04 11:10 +0200
Re: [RFC][PATCHv2 2/8] printk: introduce printing kernel thread Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-04 11:40 +0200
Re: [RFC][PATCHv2 2/8] printk: introduce printing kernel thread Pavel Machek <pavel@ucw.cz> - 2017-04-06 19:20 +0200
Re: [RFC][PATCHv2 2/8] printk: introduce printing kernel thread Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-07 07:20 +0200
Re: [RFC][PATCHv2 2/8] printk: introduce printing kernel thread Pavel Machek <pavel@ucw.cz> - 2017-04-07 09:30 +0200
Re: [RFC][PATCHv2 2/8] printk: introduce printing kernel thread Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-07 10:20 +0200
Re: [RFC][PATCHv2 2/8] printk: introduce printing kernel thread Pavel Machek <pavel@ucw.cz> - 2017-04-07 14:10 +0200
[RFC][PATCHv2 5/8] sysrq: switch to printk.emergency mode in unsafe places Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-03-29 11:30 +0200
Re: [RFC][PATCHv2 5/8] sysrq: switch to printk.emergency mode in unsafe places Petr Mladek <pmladek@suse.com> - 2017-03-31 17:40 +0200
Re: [RFC][PATCHv2 5/8] sysrq: switch to printk.emergency mode in unsafe places Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-04-01 02:10 +0200
[RFC][PATCHv2 1/8] printk: move printk_pending out of per-cpu Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-03-29 11:40 +0200
Re: [RFC][PATCHv2 1/8] printk: move printk_pending out of per-cpu Petr Mladek <pmladek@suse.com> - 2017-03-31 15:20 +0200
Re: [RFC][PATCHv2 1/8] printk: move printk_pending out of per-cpu Peter Zijlstra <peterz@infradead.org> - 2017-03-31 15:40 +0200
Re: [RFC][PATCHv2 1/8] printk: move printk_pending out of per-cpu Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-03 13:30 +0200
Re: [RFC][PATCHv2 1/8] printk: move printk_pending out of per-cpu Petr Mladek <pmladek@suse.com> - 2017-04-03 14:50 +0200
[RFC][PATCHv2 6/8] kexec: switch to printk.emergency mode in unsafe places Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-03-29 11:40 +0200
Re: [RFC][PATCHv2 6/8] kexec: switch to printk.emergency mode in unsafe places Petr Mladek <pmladek@suse.com> - 2017-03-31 17:40 +0200
[RFC][PATCHv2 8/8] printk: enable printk offloading Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-03-29 11:40 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-03-31 04:40 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-03-31 06:10 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Ye Xiaolong <xiaolong.ye@intel.com> - 2017-03-31 08:50 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-03-31 16:50 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage ebiederm@xmission.com (Eric W. Biederman) - 2017-03-31 17:40 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Jan Kara <jack@suse.cz> - 2017-04-03 11:40 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Petr Mladek <pmladek@suse.com> - 2017-04-03 12:10 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Pavel Machek <pavel@ucw.cz> - 2017-04-06 19:40 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-07 06:50 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Pavel Machek <pavel@ucw.cz> - 2017-04-07 09:20 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-07 09:50 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Pavel Machek <pavel@ucw.cz> - 2017-04-07 10:20 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-07 14:20 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Pavel Machek <pavel@ucw.cz> - 2017-04-07 14:50 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:50 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-04-07 17:20 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Peter Zijlstra <peterz@infradead.org> - 2017-04-07 17:30 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-04-07 17:50 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage ebiederm@xmission.com (Eric W. Biederman) - 2017-04-09 20:30 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-10 06:50 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Pavel Machek <pavel@ucw.cz> - 2017-04-09 12:20 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-10 07:00 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Petr Mladek <pmladek@suse.com> - 2017-04-10 14:00 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:40 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Pavel Machek <pavel@ucw.cz> - 2017-04-09 12:00 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-03 13:00 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Ye Xiaolong <xiaolong.ye@intel.com> - 2017-04-05 09:40 +0200
Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-05 10:50 +0200
Re: [RFC][PATCHv2 8/8] printk: enable printk offloading Petr Mladek <pmladek@suse.com> - 2017-04-03 17:50 +0200
Re: [RFC][PATCHv2 8/8] printk: enable printk offloading Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-04-04 14:30 +0200
[RFC][PATCHv2 4/8] pm: switch to printk.emergency mode in unsafe places Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-03-29 11:40 +0200
Re: [RFC][PATCHv2 4/8] pm: switch to printk.emergency mode in unsafe places Petr Mladek <pmladek@suse.com> - 2017-03-31 17:10 +0200
Re: [RFC][PATCHv2 4/8] pm: switch to printk.emergency mode in unsafe places Pavel Machek <pavel@ucw.cz> - 2017-04-06 19:30 +0200
Re: [RFC][PATCHv2 4/8] pm: switch to printk.emergency mode in unsafe places Andreas Mohr <andi@lisas.de> - 2017-04-09 13:00 +0200
Re: [RFC][PATCHv2 4/8] pm: switch to printk.emergency mode in unsafe places Petr Mladek <pmladek@suse.com> - 2017-04-10 14:30 +0200
Re: [RFC][PATCHv2 4/8] pm: switch to printk.emergency mode in unsafe places Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-04-10 16:40 +0200
[RFC][PATCHv2 7/8] printk: add printk emergency_mode parameter Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2017-03-29 11:40 +0200
Re: [RFC][PATCHv2 7/8] printk: add printk emergency_mode parameter Petr Mladek <pmladek@suse.com> - 2017-04-03 17:30 +0200
Re: [RFC][PATCHv2 7/8] printk: add printk emergency_mode parameter Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-04 10:30 +0200
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