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printk: wake up klogd in vprintk_emit

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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/[email protected]
To: Steven Rostedt <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: [email protected]
Signed-off-by: Sergey Senozhatsky <[email protected]>
Signed-off-by: Petr Mladek <[email protected]>
This commit is contained in:
Sergey Senozhatsky 2018-04-19 10:42:50 +09:00 • committed by Petr Mladek
commit 43a17111c2
1 changed files with 2 additions and 12 deletions
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14
kernel/printk/printk.c
View file

@ -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);