linux-kernel - [PATCH] kernel/printk.c: document possible deadlock against scheduler

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <Pine.LNX.4.64.0707040214440.11634@jikos.suse.cz>
Date:	Wed, 4 Jul 2007 02:16:03 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] kernel/printk.c: document possible deadlock against scheduler

From: Jiri Kosina <jkosina@...e.cz>

kernel/printk.c: document possible deadlock against scheduler

The printk's comment states that it can be called from every context,
which might lead to false illusion that it could be called from everywhere
without any restrictions.

This is however not true - a call to printk() could deadlock if called from
scheduler code (namely from schedule(), wake_up(), etc) on runqueue lock
when it tries to wake up klogd. Document this.

Signed-off-by: Jiri Kosina <jkosina@...e.cz>

diff --git a/kernel/printk.c b/kernel/printk.c
index 0bbdeac..a3a7d53 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -483,6 +483,9 @@ static int have_callable_console(void)
  * @fmt: format string
  *
  * This is printk().  It can be called from any context.  We want it to work.
+ * Be aware of the fact that if oops_in_progress is not set, we might try to
+ * wake klogd up which could deadlock on runqueue lock if printk() is called
+ * from scheduler code.
  *
  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
  * call the console drivers.  If we fail to get the semaphore we place the output
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/