Re: [PATCH] mm,page_alloc: Serialize warn_alloc() if schedulable.

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

On (06/05/17 16:10), Sergey Senozhatsky wrote:
[..]
> > Notice the timestamp jump between [  351.239144] and [  389.308085].
> 
> do you have a restrictive console loglevel and a ton of messages that
> were simply filtered out by console loglevel check? we still store those
> messages to the logbuf (for dmesg, etc.) and process them in console_unlock(),
> but don't print to the serial console. so, in other words,
> 
> logbuf:
> 
> 	timestamp T0	message M0		-- visible loglevel
> 	timestamp T1	message M1  		-- suppressed loglevel
> 	....
> 	timestamp T100	message M101		-- suppressed loglevel
> 	timestamp T101	message M102		-- visible loglevel
> 
> on the serial console you'll see
> 
> 	T0	M0
> 	T101	M102
> 
> which might look like a spike in timestamps (while there weren't any).
> just a thought.

does it make any difference if you disable preemption in console_unlock()?
something like below... just curious...

---

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index a1aecf44ab07..25fe408cb994 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2204,6 +2204,8 @@ void console_unlock(void)
 		return;
 	}
 
+	preempt_disable();
+
 	for (;;) {
 		struct printk_log *msg;
 		size_t ext_len = 0;
@@ -2260,9 +2262,6 @@ void console_unlock(void)
 		call_console_drivers(ext_text, ext_len, text, len);
 		start_critical_timings();
 		printk_safe_exit_irqrestore(flags);
-
-		if (do_cond_resched)
-			cond_resched();
 	}
 	console_locked = 0;
 
@@ -2274,6 +2273,8 @@ void console_unlock(void)
 
 	up_console_sem();
 
+	preempt_enable();
+
 	/*
 	 * Someone could have filled up the buffer again, so re-check if there's
 	 * something to flush. In case we cannot trylock the console_sem again,

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