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From: Jesse Barnes <jbarnes@sgi.com>
To: linux-kernel@vger.kernel.org
Subject: Re: 2.6.5-rc1-mm2
Date: Wed, 31 Mar 2004 11:02:58 -0800
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Cc: Andrew Morton <akpm@osdl.org>
References: <20040317201454.5b2e8a3c.akpm@osdl.org> <20040330113620.33d01d9c.akpm@osdl.org> <200403301144.26050.jbarnes@sgi.com>
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On Tuesday 30 March 2004 11:44 am, Jesse Barnes wrote:
> It looks like there's a bug in the sysrq implementation in the sn_serial
> driver.  Once the initial console is opened, sysrq no longer works.  All
> I've determined so far is that both CPUs in my box are in cpu_idle
> somewhere... Anyway, I'll keep looking.

Ah, now sysrq is working (just had to configure it correctly).  I've seen two
backtraces in the hangs I've seen.  The one I just reproduced looks like this:

Enabling local filesystem quotas:  [  OK  ]
Enabling swap space:  [  OK  ]
INIT: Entering runlevel: 3
Entering non-interactive startup
Starting sysstat:  [  OK  ]
Setting network parameters:  ^[SYSSysRq : Show State
[ bunch of kernel daemon traces ]
...
S10network    S a0000001000d8cf0     0  1143   1104  1156               (NOTLB)

Call Trace:
 [<a0000001000c4200>] schedule+0xda0/0x1360
                                sp=e00000387a27fdc0 bsp=e00000387a2791b8
 [<a0000001000d8cf0>] sys_wait4+0x450/0x660
                                sp=e00000387a27fdd0 bsp=e00000387a2790f0
 [<a000000100011a60>] ia64_ret_from_syscall+0x0/0x20
                                sp=e00000387a27fe30 bsp=e00000387a2790b8
initlog       S a0000001000e8650     0  1156   1143  1157               (NOTLB)

Call Trace:
 [<a0000001000c4200>] schedule+0xda0/0x1360
                                sp=e00000387af47ce0 bsp=e00000387af411a0
 [<a0000001000e8650>] schedule_timeout+0x190/0x1a0
                                sp=e00000387af47cf0 bsp=e00000387af41168
 [<a00000010072eb70>] unix_wait_for_peer+0x210/0x220
                                sp=e00000387af47d30 bsp=e00000387af41130
 [<a00000010072ee30>] unix_stream_connect+0x2b0/0xd00
                                sp=e00000387af47d90 bsp=e00000387af41098
 [<a0000001006285f0>] sys_connect+0xf0/0x140
                                sp=e00000387af47da0 bsp=e00000387af41020
 [<a000000100011a60>] ia64_ret_from_syscall+0x0/0x20
                                sp=e00000387af47e30 bsp=e00000387af41020
sysctl        Z a0000001000d7330     0  1157   1156                     (L-TLB)

Call Trace:
 [<a0000001000c4200>] schedule+0xda0/0x1360
                                sp=e00000347a5a7e20 bsp=e00000347a5a1078
 [<a0000001000d7330>] do_exit+0x490/0x500
                                sp=e00000347a5a7e30 bsp=e00000347a5a1018
 [<a0000001000d77b0>] do_group_exit+0x290/0x360
                                sp=e00000347a5a7e30 bsp=e00000347a5a0fe0
 [<a000000100011a60>] ia64_ret_from_syscall+0x0/0x20
                                sp=e00000347a5a7e30 bsp=e00000347a5a0fc8

and the CPU is in cpu_idle (somewhere, either default_idle or somewhere
along that call path).  The other failure was also a hang, and it looked
like an infinite number of page faults was being generated, something
like

...
 [<a0000001001233c0>] __free_pages+0x60/0x140
                                sp=e0000030148ebb80 bsp=e0000030148e5388
 [<a00000010012b670>] slab_destroy+0x2f0/0x3e0
                                sp=e0000030148ebb80 bsp=e0000030148e5338
 [<a000000100130120>] reap_timer_fnc+0x480/0x680
                                sp=e0000030148ebb80 bsp=e0000030148e5268
 [<a0000001000e7ee0>] run_timer_softirq+0x380/0x5c0
                                sp=e0000030148ebb90 bsp=e0000030148e51e0
 [<a0000001000dbd10>] __do_softirq+0x1d0/0x1e0
                                sp=e0000030148ebbb0 bsp=e0000030148e5160
 [<a0000001000dbda0>] do_softirq+0x80/0xe0
                                sp=e0000030148ebbb0 bsp=e0000030148e5100
 [<a000000100018300>] ia64_handle_irq+0x180/0x1c0
                                sp=e0000030148ebbb0 bsp=e0000030148e50c0
 [<a000000100011c00>] ia64_leave_kernel+0x0/0x280
                                sp=e0000030148ebbb0 bsp=e0000030148e50c0
 [<a000000100019d20>] default_idle+0xe0/0x180

or

...
 [<a00000010005de40>] mapped_kernel_page_is_present+0x100/0x120
                                sp=e0000030148eb920 bsp=e0000030148e5438
 [<a00000010005dfd0>] ia64_do_page_fault+0x170/0x960
                                sp=e0000030148eb920 bsp=e0000030148e53c8
 [<a000000100011c00>] ia64_leave_kernel+0x0/0x280
                                sp=e0000030148eb9b0 bsp=e0000030148e53c8
 [<a0000001001233c0>] __free_pages+0x60/0x140
                                sp=e0000030148ebb80 bsp=e0000030148e5388
 [<a00000010012b670>] slab_destroy+0x2f0/0x3e0
                                sp=e0000030148ebb80 bsp=e0000030148e5338
 [<a000000100130120>] reap_timer_fnc+0x480/0x680
                                sp=e0000030148ebb80 bsp=e0000030148e5268
 [<a0000001000e7ee0>] run_timer_softirq+0x380/0x5c0
                                sp=e0000030148ebb90 bsp=e0000030148e51e0

Jesse
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