Commit 43a17111 authored Apr 19, 2018 by Sergey Senozhatsky Committed by Petr Mladek Apr 25, 2018

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: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr 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 @@ again:

		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 @@ skip:

		if (console_lock_spinning_disable_and_check()) {
		printk_safe_exit_irqrestore(flags);
		goto out;
		return;
		}

		printk_safe_exit_irqrestore(flags);
		@@ -2428,10 +2422,6 @@ skip:

		if (retry && console_trylock())
		goto again;

		out:
		if (wake_klogd)
		wake_up_klogd();
		}
		EXPORT_SYMBOL(console_unlock);

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