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Date: Sat, 08 Jul 2006 08:56:03 +0800
From: "Antonino A. Daplas" <adaplas@gmail.com>
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To: Dave Jones <davej@redhat.com>, Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: framebuffer console code triggered might_sleep assertion.
References: <20060707220951.GA3356@redhat.com>
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Dave Jones wrote:
> Whilst printk'ing to both console and serial console, I got this...
> (2.6.18rc1)
> 
> 		Dave
> 
> 
> BUG: sleeping function called from invalid context at kernel/sched.c:4438
> in_atomic():0, irqs_disabled():1
> 
> Call Trace:
>  [<ffffffff80271db8>] show_trace+0xaa/0x23d
>  [<ffffffff80271f60>] dump_stack+0x15/0x17
>  [<ffffffff8020b9f8>] __might_sleep+0xb2/0xb4
>  [<ffffffff8029232e>] __cond_resched+0x15/0x55
>  [<ffffffff80267eb8>] cond_resched+0x3b/0x42
>  [<ffffffff80268c64>] console_conditional_schedule+0x12/0x14
>  [<ffffffff80368159>] fbcon_redraw+0xf6/0x160
>  [<ffffffff80369c58>] fbcon_scroll+0x5d9/0xb52
>  [<ffffffff803a43c4>] scrup+0x6b/0xd6
>  [<ffffffff803a4453>] lf+0x24/0x44
>  [<ffffffff803a7ff8>] vt_console_print+0x166/0x23d
>  [<ffffffff80295528>] __call_console_drivers+0x65/0x76
>  [<ffffffff80295597>] _call_console_drivers+0x5e/0x62
>  [<ffffffff80217e3f>] release_console_sem+0x14b/0x232
>  [<ffffffff8036acd6>] fb_flashcursor+0x279/0x2a6
>  [<ffffffff80251e3f>] run_workqueue+0xa8/0xfb
>  [<ffffffff8024e5e0>] worker_thread+0xef/0x122
>  [<ffffffff8023660f>] kthread+0x100/0x136
>  [<ffffffff8026419e>] child_rip+0x8/0x12
> 
> 

Looks like the printk buffer was flushed on release_console_sem() while
the irqs are disabled. But the console (fbcon) thinks that it's still
okay to schedule() which triggered might_sleep().

Would the attached patch help? It disables console scheduling before
calling the console drivers.

Tony

diff --git a/kernel/printk.c b/kernel/printk.c
index 9940030..f98576d 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -780,6 +780,9 @@ void release_console_sem(void)
 		up(&secondary_console_sem);
 		return;
 	}
+
+	console_may_schedule = 0;
+
 	for ( ; ; ) {
 		spin_lock_irqsave(&logbuf_lock, flags);
 		wake_klogd |= log_start - log_end;
@@ -793,7 +796,6 @@ void release_console_sem(void)
 		local_irq_restore(flags);
 	}
 	console_locked = 0;
-	console_may_schedule = 0;
 	up(&console_sem);
 	spin_unlock_irqrestore(&logbuf_lock, flags);
 	if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait)) {