linux-kernel - Re: [PATCH] Check for breakpoint in text_poke to eliminate bug

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Date:	Sun, 20 Apr 2008 01:42:06 +0300
From:	Pekka Paalanen <pq@....fi>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] Check for breakpoint in text_poke to eliminate bug_on

On Sat, 19 Apr 2008 17:58:26 -0400
Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:

> * Pekka Paalanen (pq@....fi) wrote:
> > 
> > A simple
> > echo 0 > /sys/devices/system/cpu/cpu1/online
> > echo 1 > /sys/devices/system/cpu/cpu1/online
> > 
> > produces the following kernel log (netconsole) and then after a couple
> > second hang the machine reboots:
> > 
> > [   84.678357] console [netcon0] enabled
> > [   84.679568] netconsole: network logging started
> > [  232.812335] CPU 1 is now offline
> > [  232.812678] lockdep: fixing up alternatives.
> > [  232.813051] SMP alternatives: switching to UP code
> > [  268.447582] lockdep: fixing up alternatives.
> > [  268.447903] SMP alternatives: switching to SMP code
> > [  268.459462] Booting processor 1/1 ip 6000
> > 
> > My kernel is sched-devel/latest git tree with Desnoyers' patch, and my
> > patches that touch only arch/x86/mm/mmio-mod.c.
> > The machine is Thinkpad T61 with:
> > 
> > processor	: 0
> > vendor_id	: GenuineIntel
> > cpu family	: 6
> > model		: 15
> > model name	: Intel(R) Core(TM)2 Duo CPU     T7300  @ 2.00GHz
> > stepping	: 10
> > cpu MHz		: 2001.000
> > cache size	: 4096 KB
> > physical id	: 0
> > siblings	: 2
> > core id		: 0
> > cpu cores	: 2
> > apicid		: 0
> > initial apicid	: 0
> > fpu		: yes
> > fpu_exception	: yes
> > cpuid level	: 10
> > wp		: yes
> > flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
> > cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx
> > lm constant_tsc arch_perfmon pebs bts rep_good pni monitor ds_cpl vmx est
> > tm2 ssse3 cx16 xtpr lahf_lm ida
> > bogomips	: 3997.03
> > clflush size	: 64
> > cache_alignment	: 64
> > address sizes	: 36 bits physical, 48 bits virtual
> > power management:
> > 
> > processor	: 1
> > vendor_id	: GenuineIntel
> > cpu family	: 6
> > model		: 15
> > model name	: Intel(R) Core(TM)2 Duo CPU     T7300  @ 2.00GHz
> > stepping	: 10
> > cpu MHz		: 2001.000
> > cache size	: 4096 KB
> > physical id	: 0
> > siblings	: 2
> > core id		: 1
> > cpu cores	: 2
> > apicid		: 1
> > initial apicid	: 1
> > fpu		: yes
> > fpu_exception	: yes
> > cpuid level	: 10
> > wp		: yes
> > flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
> > cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx
> > lm constant_tsc arch_perfmon pebs bts rep_good pni monitor ds_cpl vmx est
> > tm2 ssse3 cx16 xtpr lahf_lm ida
> > bogomips	: 3991.26
> > clflush size	: 64
> > cache_alignment	: 64
> > address sizes	: 36 bits physical, 48 bits virtual
> > power management:
> > 
> > Any help would be appreciated.
> > 
> > 
> > Thanks.
> 
> This patch should bring more consistency checks to text_poke, can you
> give it a try ?
> 
> Hm, actually, I think it contains the fix you are looking for.
> 
> kernel_text_address -> core_kernel_text will probably make everything go
> smoothly.
> 
> Mathieu
> 
> 
> Check for breakpoint in text_poke to eliminate bug_on
> 
> It's ok to modify an instruction non-atomically (multiple memory accesses to a
> large and/or non aligned instruction) *if and only if* we have inserted a
> breakpoint at the beginning of the instruction.
> 
> Also change kernel_text_address (bogus) check to core_kernel_text.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> ---
>  arch/x86/kernel/alternative.c |   49 ++++++++++++++++++++++++------------------
>  1 file changed, 29 insertions(+), 20 deletions(-)

Sorry, no change.

[   93.315242] netconsole: network logging started
[   95.797496] eth0: no IPv6 routers present
[  127.472213] CPU 1 is now offline
[  127.472547] lockdep: fixing up alternatives.
[  127.472923] SMP alternatives: switching to UP code
[  134.709384] lockdep: fixing up alternatives.
[  134.709701] SMP alternatives: switching to SMP code
[  134.721344] Booting processor 1/1 ip 6000

few seconds pause and it reboots. A working patch in six minutes would
have been quite awesome :-)


Thanks.

-- 
Pekka Paalanen
http://www.iki.fi/pq/
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