linux-kernel - v2.6.19-rc1 regression: printk missing klogd wakeup

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Date:	Sat, 07 Oct 2006 01:03:08 +0200
From:	Tilman Schmidt <tilman@...p.cc>
To:	LKML <linux-kernel@...r.kernel.org>
CC:	mingo@...e.hu
Subject: v2.6.19-rc1 regression: printk missing klogd wakeup

Unsurprisingly, v2.6.19-rc1 still contains the problem I reported
for v2.6.18-rc1 under the subject "Linux v2.6.18-rc1: printk delays"
and later (unfortunately not before it made it into v2.6.18) tracked
down through bisecting to

[a0f1ccfd8d37457a6d8a9e01acebeefcdfcc306e] lockdep: do not recurse in printk

Problem description:
> While X is running, output from printk() appears in syslog (eg.
> /var/log/messages) only after a key is pressed on the system keyboard,
> even though it is visible with dmesg immediately.
(from lkml message <450BF1CC.2070309@...p.cc> - see that message
for further details)

The problem did not exist in 2.6.17, so I think it qualifies as a
regression.

The following naive patch fixes the problem for me, without any
apparent ill effects (ie. the menace of lockup never manifested
itself):

--- a/kernel/printk.c   2006-10-07 00:51:09.000000000 +0200
+++ b/kernel/printk.c   2006-10-07 00:51:41.000000000 +0200
@@ -826,8 +826,7 @@ void release_console_sem(void)
                 * from within the scheduler code, then do not lock
                 * up due to self-recursion:
                 */
-               if (!lockdep_internal())
-                       wake_up_interruptible(&log_wait);
+               wake_up_interruptible(&log_wait);
        }
 }
 EXPORT_SYMBOL(release_console_sem);

But I guess for a proper fix the if() condition should rather be
refined a bit than thrown out completely.

-- 
Tilman Schmidt                          E-Mail: tilman@...p.cc
Bonn, Germany
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