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

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Message-ID: <20080420000509.GA7496@Krystal>
Date:	Sat, 19 Apr 2008 20:05:09 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Pekka Paalanen <pq@....fi>
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

* Pekka Paalanen (pq@....fi) wrote:
> 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 :-)
> 

Hrm, I'll have to do some more tests.

Can you mail you .config please ?

Mathieu

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

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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