From: "tiejun.chen" <tiejun.chen@windriver.com>
To: <ananth@in.ibm.com>
Cc: "tiejun.chen" <tiejun.chen@windriver.com>, linuxppc-dev@ozlabs.org
Subject: Re: [v2 PATCH 2/2] booke/kprobe: remove unnecessary preempt_enable_no_resched
Date: Mon, 11 Jul 2011 19:28:31 +0800 [thread overview]
Message-ID: <4E1ADE5F.9030507@windriver.com> (raw)
In-Reply-To: <4E1AB59A.6050002@windriver.com>
tiejun.chen wrote:
> Ananth N Mavinakayanahalli wrote:
>> On Mon, Jul 11, 2011 at 10:39:35AM +0800, Tiejun Chen wrote:
>>> When enable CONFIG_PREEMPT we will trigger the following call trace:
>>>
>>> BUG: scheduling while atomic: swapper/1/0x10000000
>>> ...
>>>
>>> krpobe always goes through the following path:
>>>
>>> program_check_exception()
>>> |
>>> + notify_die(DIE_BPT, "breakpoint",...)
>>> |
>>> + kprobe_handler()
>>> |
>>> + preempt_disable();
>>> + break_handler() <- preempt_enable_no_resched()
>>> + emulate_step()
>>> + preempt_enable_no_resched()
>>> ...
>>> exit
>>>
>>> We should remove unnecessary preempt_enable_no_resched() inside of break_handler()
>>> since looks longjmp_break_handler() always go the above path.
>> The current code is correct. Reasoning follows...
>>
>> setjmp_pre_handler() and longjmp_break_handler() are used only for
>> jprobes. In the case of a jprobe, the code flow would be:
>>
>> bp hit -> kprobe_handler() -> preempt_disable() -> setjmp_pre_handler()
>> (not that since this routine returns 1, we skip sstep here) -> jp->entry()
>> -> jprobe_return() -> bp hit -> kprobe_handler() -> preempt_disable() again
>> -> longjmp_break_handler() -> preempt_enable() -> sstep -> preempt_enable()
>> (for the second kprobe_handler() entry).
>>
>> You could verify this with a preempt_count() printk with a
>> CONFIG_PREEMPT=y kernel.
>>
>>> Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
>> Nack, sorry :-)
>
> You're right.
>
> When use EXC_LEVEL_EXCEPTION_PROLOG for Critical/Machine check, if the exception
> came from kernel mode, we copy thread_info flags, *preempt*, and task pointer
> from the process thread_info. So here I steal EXC_LEVEL_EXCEPTION_PROLOG for
> Program Exception, preempt count would be corrupted incorrectly.
Looks I miss the specific return-from-program-exc to restore those necessary
thread information like we did for debug exception with ret_from_debug_exc when
use EXC_LEVEL_EXCEPTION_PROLOG for debug exception.
Will update this on v3.
Tiejun
>
> Thanks
> Tiejun
>
>> Ananth
>>
>
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev
>
prev parent reply other threads:[~2011-07-11 11:29 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-11 2:39 [v2 PATCH 1/2] booke/kprobe: make program exception to use one dedicated exception stack Tiejun Chen
2011-07-11 2:39 ` [v2 PATCH 2/2] booke/kprobe: remove unnecessary preempt_enable_no_resched Tiejun Chen
2011-07-11 2:39 ` v2 booke/kprobe: Fix stack corrupt issue when kprobe 'stwu' Tiejun Chen
2011-07-11 5:55 ` [v2 PATCH 2/2] booke/kprobe: remove unnecessary preempt_enable_no_resched Ananth N Mavinakayanahalli
2011-07-11 8:34 ` tiejun.chen
2011-07-11 11:28 ` tiejun.chen [this message]
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