From 43a17111c2553925f65e7be9b9c3f9d90cf29a8b Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Thu, 19 Apr 2018 10:42:50 +0900 Subject: [PATCH] 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 Cc: Andrew Morton Cc: Peter Zijlstra Cc: Tejun Heo Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek --- kernel/printk/printk.c | 14 ++------------ 1 file changed, 2 insertions(+), 12 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 704e55129c3a..fba995b305b1 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -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);