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

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Message-Id: <20161227141611.940-5-sergey.senozhatsky@gmail.com>
Date:   Tue, 27 Dec 2016 23:16:07 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        Calvin Owens <calvinowens@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        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,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: [PATCHv7 4/8] 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>
Reviewed-by: Petr Mladek <pmladek@...e.com>
---
 kernel/printk/printk_safe.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index efc89a4e9df5..054c9128ade0 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -113,14 +113,12 @@ static int printk_safe_log_store(struct printk_safe_seq_buf *s,
 static 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