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From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] blk-mq: Remove get_cpu() in
 __blk_mq_delay_run_hw_queue().
Message-ID: <YguYbC0540CecccG@linutronix.de>
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On 2022-02-15 19:58:03 [+0800], Ming Lei wrote:
> On Tue, Feb 15, 2022 at 10:31:49AM +0100, Sebastian Andrzej Siewior wrote:
> > On 2022-02-15 17:23:45 [+0800], Ming Lei wrote:
> > > > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > > > index 1adfe4824ef5e..90217f1b09add 100644
> > > > --- a/block/blk-mq.c
> > > > +++ b/block/blk-mq.c
> > > > @@ -2040,14 +2040,10 @@ static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
> > > >  		return;
> > > >  
> > > >  	if (!async && !(hctx->flags & BLK_MQ_F_BLOCKING)) {
> > > > -		int cpu = get_cpu();
> > > 
> > > Did you observe the warning triggered?  might_sleep_if(true) in
> > > __blk_mq_run_dispatch_ops() is only supposed to be run in case of
> > > (hctx->flags & BLK_MQ_F_BLOCKING).
> > 
> > I haven't seen it triggering but if that call chain is possible then it
> > will triggert due to get_cpu().
> 
> As I mentioned, the call chain isn't possible.

Why not? Is BLK_MQ_F_BLOCKING and blk_queue_has_srcu() exclusive?

> Thanks,
> Ming

Sebastian