linux-kernel - Re: [PATCH RT 1/2] tasklet: Address a race resulting in double-enqueue

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Message-ID: <D6892A4E-18F7-4EB7-BA09-BD4DF9079BDE@gmail.com>
Date:   Tue, 09 Jun 2020 19:37:31 +0300
From:   Ramon Fried <rfried.dev@...il.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Tom Zanussi <zanussi@...nel.org>
CC:     LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        John Kacur <jkacur@...hat.com>, Daniel Wagner <wagi@...om.org>,
        Clark Williams <williams@...hat.com>,
        Zhang Xiao <xiao.zhang@...driver.com>
Subject: Re: [PATCH RT 1/2] tasklet: Address a race resulting in double-enqueue



On June 9, 2020 7:34:46 PM GMT+03:00, Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:
>On 2020-06-09 11:17:53 [-0500], Tom Zanussi wrote:
>> Hi Sebastian,
>Hi Tom,
>
>> I did find a problem with the patch when configured as !SMP since in
>> that case the RUN flag is never set (will send a patch for that
>> shortly), but that wouldn't be the case here.
>
>How?
>
>| #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL)
>| static inline int tasklet_trylock(struct tasklet_struct *t)
>| {
>|         return !test_and_set_bit(TASKLET_STATE_RUN, &(t)->state);
>| }
>
>I can't tell from the backtrace if he runs with RT or without but I
>assumed RT. But yes, for !SMP && !RT it would explain it.
PREEMT_FULL is enabled. 
I'm working on getting symbols for this trace, this is a crash kernel so everything is stripped naked. 
Thanks, Ramon
>
>> It would help to be able to reproduce it, but I haven't been able to
>> yet.
>> 
>> Tom
>> 
>Sebastian

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