linux-kernel - Re: [PATCH v3 30/30] locking/lockdep: Remove irq-safe to irq-unsafe read check

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Date:   Wed, 10 Jul 2019 14:30:07 +0800
From:   Yuyang Du <duyuyang@...il.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Bart Van Assche <bvanassche@....org>, ming.lei@...hat.com,
        Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Waiman Long <longman@...hat.com>, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v3 30/30] locking/lockdep: Remove irq-safe to irq-unsafe
 read check

Thanks for review.

On Wed, 10 Jul 2019 at 13:30, Boqun Feng <boqun.feng@...il.com> wrote:
>
> On Fri, Jun 28, 2019 at 05:15:28PM +0800, Yuyang Du wrote:
> > We have a lockdep warning:
> >
> >   ========================================================
> >   WARNING: possible irq lock inversion dependency detected
> >   5.1.0-rc7+ #141 Not tainted
> >   --------------------------------------------------------
> >   kworker/8:2/328 just changed the state of lock:
> >   0000000007f1a95b (&(&host->lock)->rlock){-...}, at: ata_bmdma_interrupt+0x27/0x1c0 [libata]
> >   but this lock took another, HARDIRQ-READ-unsafe lock in the past:
> >    (&trig->leddev_list_lock){.+.?}
> >
> > and interrupts could create inverse lock ordering between them.
> >
> > other info that might help us debug this:
> >    Possible interrupt unsafe locking scenario:
> >
> >          CPU0                    CPU1
> >          ----                    ----
> >     lock(&trig->leddev_list_lock);
> >                                  local_irq_disable();
> >                                  lock(&(&host->lock)->rlock);
> >                                  lock(&trig->leddev_list_lock);
> >     <Interrupt>
> >       lock(&(&host->lock)->rlock);
> >
> >  *** DEADLOCK ***
> >
> > This splat is a false positive, which is enabled by the addition of
>
> If so, I think the better way is to reorder this patch before recursive
> read lock suppport, for better bisect-ability.

Good suggestion.

Thanks,
Yuyang