From: Darren Hart <dvhltc@us.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>,
Gautham R Shenoy <ego@in.ibm.com>,
Steven Rostedt <rostedt@goodmis.org>,
linuxppc-dev@ozlabs.org, Will Schmidt <willschm@us.ibm.com>,
Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH][RFC] preempt_count corruption across H_CEDE call with CONFIG_PREEMPT on pseries
Date: Tue, 10 Aug 2010 15:36:20 -0700 [thread overview]
Message-ID: <4C61D464.5090307@us.ibm.com> (raw)
In-Reply-To: <alpine.LFD.2.00.1007222028420.2616@localhost.localdomain>
On 07/22/2010 11:38 AM, Thomas Gleixner wrote:
> On Thu, 22 Jul 2010, Darren Hart wrote:
>
>> Also of interest is that this path
>> cpu_idle()->cpu_die()->pseries_mach_cpu_die() to start_secondary()
>> enters with a preempt_count=1 if it wasn't corrupted across the hcall.
>
> That triggers the problem as well. preempt_count needs to be 0 when
> entering start_secondary(). So I really wonder how that ever worked.
>
>> The early boot path from _start however appears to call
>> start_secondary() with a preempt_count of 0.
>
> Which is correct.
>
>> The following patch is most certainly not correct, but it does eliminate
>
> It is correct, but i think it is incomplete as other portions of the
> thread_info on the stack might be in some weird state as well.
Just FYI, I took a look at the stack pointers as well as all the fields
in the thread_info struct. The only one that changes is preempt_count.
The previous value of preempt_count doesn't impact the value after cede.
An initial value of 0, 1, or 4 all result in an after-cede value of
0xffffffff. I also added 32 bits of padding on either side of the
preempt_count in case the change was accidental - it wasnt', the padded
values remained unchanged across the cede call while the preempt_count
still changed to 0xffffffff.
--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
next prev parent reply other threads:[~2010-08-10 22:36 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-07-22 18:24 [PATCH][RFC] preempt_count corruption across H_CEDE call with CONFIG_PREEMPT on pseries Darren Hart
2010-07-22 18:36 ` Darren Hart
2010-07-22 18:38 ` Thomas Gleixner
2010-08-10 22:36 ` Darren Hart [this message]
2010-07-22 22:25 ` Benjamin Herrenschmidt
2010-07-22 23:57 ` Darren Hart
2010-07-23 4:44 ` Darren Hart
2010-07-23 5:08 ` Vaidyanathan Srinivasan
2010-07-23 5:11 ` Benjamin Herrenschmidt
2010-07-23 7:07 ` Vaidyanathan Srinivasan
2010-08-05 4:45 ` Darren Hart
2010-08-05 11:06 ` Vaidyanathan Srinivasan
2010-08-05 12:26 ` Thomas Gleixner
2010-07-23 5:09 ` Benjamin Herrenschmidt
2010-08-06 2:19 ` Darren Hart
2010-08-06 5:09 ` Vaidyanathan Srinivasan
2010-08-06 7:13 ` Darren Hart
2010-07-23 14:39 ` Will Schmidt
2010-08-04 13:44 ` Darren Hart
2010-08-19 15:58 ` Ankita Garg
2010-08-19 18:58 ` Will Schmidt
2010-08-23 22:20 ` Darren Hart
2010-08-31 7:12 ` Darren Hart
2010-09-01 5:54 ` Michael Ellerman
2010-09-01 15:10 ` Darren Hart
2010-09-01 18:47 ` Darren Hart
2010-09-01 19:59 ` Steven Rostedt
2010-09-01 20:42 ` Darren Hart
2010-09-02 1:02 ` Michael Neuling
2010-09-02 4:06 ` Steven Rostedt
2010-09-02 6:04 ` Darren Hart
2010-09-03 20:10 ` Will Schmidt
2010-09-02 23:04 ` Michael Neuling
2010-09-03 0:08 ` Darren Hart
2010-09-02 3:46 ` Michael Neuling
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