linux-kernel - Re: [PATCHv7 4/8] printk: always use deferred printk when flush printk

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Message-ID: <20170206164253.GA463@tigerII.localdomain>
Date:   Tue, 7 Feb 2017 01:42:53 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        Calvin Owens <calvinowens@...com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Hurley <peter@...leysoftware.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv7 4/8] printk: always use deferred printk when flush
 printk_safe lines

On (02/06/17 08:27), Steven Rostedt wrote:
[..]
> > > > just in case, the patch (which I prefer to be ignored)  
> > > 
> > > let's keep printk_safe_flush_line().  
> > 
> > I do not have strong opinion but I would slightly prefer
> > to keep the helper function. The use of printk_deferred()
> > is a bit tricky and it is better to have only one copy.
> > 
> > Steven, could you live with the original patch, please?
> 
> Sure, but make it into a static inline.

well, I'll be surprised if gcc doesn't inline that simple one-liner.

attached. no conflicts, the patch can replace 0004.

===8<===8<===

>From 69bbb0f436a2a89ec41a5831c03490e0a78ce12e Mon Sep 17 00:00:00 2001
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Date: Tue, 27 Dec 2016 23:16:07 +0900
Subject: [PATCH] printk: always use deferred printk when flush printk_safe
 lines

Always use printk_deferred() in printk_safe_flush_line().
Flushing can be done from NMI or printk_safe contexts (when
we are in panic), so we can't call console drivers, yet still
want to store the messages in the logbuf buffer. Therefore we
use a deferred printk version.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Suggested-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 kernel/printk/printk_safe.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index efc89a4e9df5..5214d326d3ba 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -110,17 +110,15 @@ static int printk_safe_log_store(struct printk_safe_seq_buf *s,
 	return add;
 }
 
-static void printk_safe_flush_line(const char *text, int len)
+static inline void printk_safe_flush_line(const char *text, int len)
 {
 	/*
-	 * The buffers are flushed in NMI only on panic.  The messages must
-	 * go only into the ring buffer at this stage.  Consoles will get
-	 * explicitly called later when a crashdump is not generated.
+	 * Avoid any console drivers calls from here, because we may be
+	 * in NMI or printk_safe context (when in panic). The messages
+	 * must go only into the ring buffer at this stage.  Consoles will
+	 * get explicitly called later when a crashdump is not generated.
 	 */
-	if (in_nmi())
-		printk_deferred("%.*s", len, text);
-	else
-		printk("%.*s", len, text);
+	printk_deferred("%.*s", len, text);
 }
 
 /* printk part of the temporary buffer line by line */
-- 
2.11.0