linux-kernel - [PATCHv3 47/50] kdb: Don't play with console

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Message-Id: <20200418201944.482088-48-dima@arista.com>
Date:   Sat, 18 Apr 2020 21:19:41 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Douglas Anderson <dianders@...omium.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        kgdb-bugreport@...ts.sourceforge.net
Subject: [PATCHv3 47/50] kdb: Don't play with console_loglevel

Print the stack trace with KERN_EMERG - it should be always visible.

Playing with console_loglevel is a bad idea as there may be more
messages printed than wanted. Also the stack trace might be not printed
at all if printk() was deferred and console_loglevel was raised back
before the trace got flushed.

Unfortunately, after rebasing on commit 2277b492582d ("kdb: Fix stack
crawling on 'running' CPUs that aren't the master"), kdb_show_stack()
uses now kdb_dump_stack_on_cpu(), which for now won't be converted as it
uses dump_stack() instead of show_stack().

Convert for now the branch that uses show_stack() and remove
console_loglevel exercise from that case.

Cc: Daniel Thompson <daniel.thompson@...aro.org>
Cc: Douglas Anderson <dianders@...omium.org>
Cc: Jason Wessel <jason.wessel@...driver.com>
Cc: kgdb-bugreport@...ts.sourceforge.net
Acked-by: Daniel Thompson <daniel.thompson@...aro.org>
Reviewed-by: Douglas Anderson <dianders@...omium.org>
Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
 kernel/debug/kdb/kdb_bt.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c
index 3de0cc780c16..43f5dcd2b9ac 100644
--- a/kernel/debug/kdb/kdb_bt.c
+++ b/kernel/debug/kdb/kdb_bt.c
@@ -21,17 +21,18 @@
 
 static void kdb_show_stack(struct task_struct *p, void *addr)
 {
-	int old_lvl = console_loglevel;
-
-	console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
 	kdb_trap_printk++;
 
-	if (!addr && kdb_task_has_cpu(p))
+	if (!addr && kdb_task_has_cpu(p)) {
+		int old_lvl = console_loglevel;
+
+		console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
 		kdb_dump_stack_on_cpu(kdb_process_cpu(p));
-	else
-		show_stack(p, addr);
+		console_loglevel = old_lvl;
+	} else {
+		show_stack_loglvl(p, addr, KERN_EMERG);
+	}
 
-	console_loglevel = old_lvl;
 	kdb_trap_printk--;
 }
 
-- 
2.26.0