From: yzhu1 <Yanjun.Zhu@windriver.com>
To: David Smith <dsmith@redhat.com>, <systemtap@sourceware.org>
Subject: Re: [PATCH 1/1] stp: rt: replace spin_lock with stp style lock and use STP_ALLOC_FLAGS
Date: Wed, 28 Oct 2015 02:30:00 -0000 [thread overview]
Message-ID: <56303328.5030603@windriver.com> (raw)
In-Reply-To: <562E9AE0.6030501@redhat.com>
On 10/27/2015 05:28 AM, David Smith wrote:
> On 10/25/2015 10:19 PM, yzhu1 wrote:
>> Hi, David
>>
>> I do not have this backtrace. Because STP_ALLOC_SLEEP_FLAGS will cause
>> kmalloc sleep,
>> so I replaced it with STP_ALLOC_FLAGS.
> Evidently I'm not explaining myself well, I'll try again in more detail.
>
> We've got 2 sets of allocation flags in systemtap:
>
> STP_ALLOC_FLAGS: These are the default flags and allocations using this
> set of flags will not sleep.
>
> STP_ALLOC_SLEEP_FLAGS: These flags are only supposed to be used from
> contexts where it is safe to sleep (like begin probes).
>
> Here's the big question - on the realtime kernel, is it ever safe to sleep?
>
> If the answer to the previous question is "no", then your change is correct.
>
> If the answer to the previous question is "yes", then your change isn't
> correct. Instead, we need to look at uses of STP_ALLOC_SLEEP_FLAGS,
> because we're using the wrong set of flags somewhere. We're using
> STP_ALLOC_SLEEP_FLAGS in an allocation that should be using STP_ALLOC_FLAGS.
>
> I see 6 uses of STP_ALLOC_SLEEP_FLAGS in the systemtap source. If we
> can't get a backtrace, then I'll need you to change the 6 uses of
> STP_ALLOC_SLEEP_FLAGS to STP_ALLOC_FLAGS one at a time to figure out
> which use of STP_ALLOC_SLEEP_FLAGS isn't correct.
>
> Thanks for continuing to work this problem.
Hi, All
OK. I will do.
Zhu Yanjun
>
>
>> Zhu Yanjun
>>
>> On 10/23/2015 12:34 AM, David Smith wrote:
>>> On 10/22/2015 02:46 AM, Zhu Yanjun wrote:
>>>> -rt mode spin lock lead to __might_sleep calltrace.
>>>> Replacing spin lock with stp type raw lock and
>>>> changing STP_ALLOC_SLEEP_FLAGS to STP_ALLOC_FLAGS solves the problem.
>>> In general, this patch looks fine. However, I'm not too sure about the
>>> STP_ALLOC_SLEEP_FLAGS bit. Can show us a backtrace that happens with
>>> your spinlock changes but without the alloc flags changes or explain why
>>> the alloc flags change is necessary? It could be that we're using the
>>> wrong set of flags in the caller.
>>>
>>> Thanks.
>>>
>
next prev parent reply other threads:[~2015-10-28 2:30 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-22 7:45 Zhu Yanjun
2015-10-22 7:53 ` yzhu1
2015-10-23 4:04 ` Santosh Shukla
2015-10-26 7:03 ` yzhu1
2015-10-26 8:25 ` yzhu1
2015-10-26 8:43 ` Santosh Shukla
2015-11-17 7:38 ` yzhu1
2015-11-17 7:52 ` Santosh Shukla
2015-10-22 16:34 ` David Smith
2015-10-26 3:19 ` yzhu1
2015-10-26 21:28 ` David Smith
2015-10-27 13:52 ` Frank Ch. Eigler
2015-10-28 2:30 ` yzhu1 [this message]
2015-10-28 17:09 ` David Smith
2015-11-17 8:09 stp: rt: replace spin_lock with stp style lock and use yzhu1
2015-11-17 8:09 ` [PATCH 1/1] stp: rt: replace spin_lock with stp style lock and use STP_ALLOC_FLAGS yzhu1
2015-11-17 16:45 ` David Smith
2015-11-18 8:14 ` yzhu1
2015-11-18 17:14 ` David Smith
2015-11-19 7:53 ` yzhu1
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