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>

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 704e551..fba995b 100644 (file)
--- 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 @@ 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);