linux-kernel - real time hang w/ latency tracing

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Message-Id: <1175626625.10738.21.camel@imap.mvista.com>
Date:	Tue, 03 Apr 2007 11:57:05 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	mingo@...e.hu
Cc:	linux-kernel@...r.kernel.org
Subject: real time hang w/ latency tracing


With 2.6.21-rc5-rt8 / i386 . If I disable wakeup timing , and enable
interrupt off timing with latency tracing I can cause,

BUG: scheduling with irqs disabled: IRQ-16/0x00000000/909
caller is rt_spin_lock_slowlock+0x94/0x190
 [<c010577a>] show_trace_log_lvl+0x3a/0x60
 [<c0105fdd>] show_trace+0x2d/0x30
 [<c01060c7>] dump_stack+0x27/0x30
 [<c03f52db>] schedule+0x12b/0x130
 [<c03f6314>] rt_spin_lock_slowlock+0x94/0x190
 [<c03f6b35>] rt_spin_lock+0x25/0x30
 [<c02f19bf>] serial8250_console_write+0x16f/0x190
 [<c012b3aa>] __call_console_drivers+0x7a/0xa0
 [<c012b427>] _call_console_drivers+0x57/0xa0
 [<c012b58d>] release_console_sem+0xdd/0x1e0
 [<c012bd46>] vprintk+0x226/0x3b0
 [<c012bef0>] printk+0x20/0x30
 [<c0158d29>] print_traces+0x49/0x100
 [<c0105792>] show_trace_log_lvl+0x52/0x60
 [<c0105fdd>] show_trace+0x2d/0x30
 [<c01060c7>] dump_stack+0x27/0x30
 [<c0158481>] check_critical_timing+0x2b1/0x380
 [<c01585f6>] trace_hardirqs_on+0xa6/0xc0
 [<c01046e5>] restore_nocheck+0x12/0x15
 =======================

I do this by running,

echo 1 > /proc/sys/kernel/preempt_thresh

which clearly causes loads of output .. Then while the output is
screaming along I hold down the left arrow key and eventually the
message above starts to appear often .. Then the system hangs.

Also I'm using an NFS root which might help to bring out the error ..

Daniel

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