linux-kernel - Re: [RFC PATCH 14/16] irq: Add support for core-wide protection of IRQ and softirq

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Date:   Sat, 18 Jul 2020 13:05:10 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>, mingo@...nel.org,
        pjt@...gle.com, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, subhra.mazumdar@...cle.com,
        fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
        Phil Auld <pauld@...hat.com>, Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>, vineethrp@...il.com,
        Chen Yu <yu.c.chen@...el.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Tim Chen <tim.c.chen@...el.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [RFC PATCH 14/16] irq: Add support for core-wide protection of
 IRQ and softirq

On Sat, Jul 18, 2020 at 01:37:50AM +0200, Thomas Gleixner wrote:
> "Li, Aubrey" <aubrey.li@...ux.intel.com> writes:
> > On 2020/7/1 5:32, Vineeth Remanan Pillai wrote:
> >
> > We saw a lot of soft lockups on the screen when we tested v6.
> >
> > [  186.527883] watchdog: BUG: soft lockup - CPU#86 stuck for 22s! [uperf:5551]
> > [  186.535884] watchdog: BUG: soft lockup - CPU#87 stuck for 22s! [uperf:5444]
> > [  186.555883] watchdog: BUG: soft lockup - CPU#89 stuck for 22s! [uperf:5547]
> > [  187.547884] rcu: INFO: rcu_sched self-detected stall on CPU
> > [  187.553760] rcu: 	40-....: (14997 ticks this GP) idle=49a/1/0x4000000000000002 softirq=1711/1711 fqs=7279 
> > [  187.564685] NMI watchdog: Watchdog detected hard LOCKUP on cpu 14
> > [  187.564723] NMI watchdog: Watchdog detected hard LOCKUP on cpu 38
> >
> > The problem is gone when we reverted this patch. We are running multiple
> > uperf threads(equal to cpu number) in a cgroup with coresched enabled.
> > This is 100% reproducible on our side.
> 
> ROTFL. I just predicted that from staring at the patch ....

Yes, sorry. It got fixed in the below patch which I was about to share before
you sent this email.  However, it still has (not yet) addressed the new
comments from you we have to discuss (will reply to that email).

Its purely a dirty test patch but it makes Aubrey's deadlock go away.
Basically, I moved the waiting code to prepare_exit_to_usermode() which
removes the lock vs wait dependencies. I will work on moving the code to the
right place based on the suggestions in the other email.

https://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux.git/commit/?h=sched/core-sched-fix-irq-deadlocks-v1&id=8857a261f3305887b063001c6c899869206667b6

thanks,

 - Joel