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Commit 43a17111 authored by Sergey Senozhatsky's avatar Sergey Senozhatsky Committed by Petr Mladek
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printk: wake up klogd in vprintk_emit 

We wake up klogd very late - only when current console_sem owner
is done pushing pending kernel messages to the serial/net consoles.
In some cases this results in lost syslog messages, because kernel
log buffer is a circular buffer and if we don't wakeup syslog long
enough there are chances that logbuf simply will wrap around.

The patch moves the klogd wake up call to vprintk_emit(), which is
the only legit way for a kernel message to appear in the logbuf,
right after the attempt to handle consoles. As a result, klogd
will get waken either after flushing the new message to consoles
or immediately when consoles are still busy with older messages.

Link: http://lkml.kernel.org/r/20180419014250.5692-1-sergey.senozhatsky@gmail.com


To: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
parent 357aa6ae

kernel/printk/printk.c

+2 −12
Original line number Diff line number Diff line
@@ -1907,6 +1907,7 @@ asmlinkage int vprintk_emit(int facility, int level, 
		preempt_enable();

	}



	wake_up_klogd();

	return printed_len;

}

EXPORT_SYMBOL(vprintk_emit);
@@ -2288,9 +2289,7 @@ void console_unlock(void) 
{

	static char ext_text[CONSOLE_EXT_LOG_MAX];

	static char text[LOG_LINE_MAX + PREFIX_MAX];

	static u64 seen_seq;

	unsigned long flags;

	bool wake_klogd = false;

	bool do_cond_resched, retry;



	if (console_suspended) {
@@ -2334,11 +2333,6 @@ void console_unlock(void) 


		printk_safe_enter_irqsave(flags);

		raw_spin_lock(&logbuf_lock);

		if (seen_seq != log_next_seq) {

			wake_klogd = true;

			seen_seq = log_next_seq;

		}



		if (console_seq < log_first_seq) {

			len = sprintf(text, "** %u printk messages dropped **\n",

				      (unsigned)(log_first_seq - console_seq));
@@ -2396,7 +2390,7 @@ void console_unlock(void) 


		if (console_lock_spinning_disable_and_check()) {

			printk_safe_exit_irqrestore(flags);

			goto out;

			return;

		}



		printk_safe_exit_irqrestore(flags);
@@ -2428,10 +2422,6 @@ void console_unlock(void) 


	if (retry && console_trylock())

		goto again;



out:

	if (wake_klogd)

		wake_up_klogd();

}

EXPORT_SYMBOL(console_unlock);