From mboxrd@z Thu Jan  1 00:00:00 1970
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH 1/6] sched: Unbreak wakeups
Date: Wed, 2 Jun 2021 15:58:04 +0200
Message-ID: <YLeObHTKKDGd3pdA@kroah.com>
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@redhat.com>, Vincent Guittot <vincent.guittot@linaro.org>, Dietmar Eggemann <dietmar.eggemann@arm.com>, Steven Rostedt <rostedt@goodmis.org>, Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>, Daniel Bristot de Oliveira <bristot@redhat.com>, Borislav Petkov <bp@alien8.de>, x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>, Jens Axboe <axboe@kernel.dk>, Alasdair Kergon <agk@redhat.com>, Mike Snitzer <snitzer@redhat.com>, dm-devel@redhat.com, "David S. Miller" <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>, Felipe Balbi <balbi@kernel.org>, Alexander Viro <viro@zeniv.linux.org.uk>, Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>

On Wed, Jun 02, 2021 at 03:12:26PM +0200, Peter Zijlstra wrote:
> Remove broken task->state references and let wake_up_process() DTRT.
> 
> The anti-pattern in these patches breaks the ordering of ->state vs
> COND as described in the comment near set_current_state() and can lead
> to missed wakeups:
> 
> 	(OoO load, observes RUNNING)<-.
> 	for (;;) {                    |
> 	  t->state = UNINTERRUPTIBLE; |
> 	  smp_mb();          ,-----> ,' (OoO load, observed !COND)
>                              |       |
> 	                     |       |	COND = 1;
> 			     |	     `- if (t->state != RUNNING)
>                              |		  wake_up_process(t); // not done
> 	  if (COND) ---------'
> 	    break;
> 	  schedule(); // forever waiting
> 	}
> 	t->state = TASK_RUNNING;
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  drivers/net/ethernet/qualcomm/qca_spi.c |    6 ++----
>  drivers/usb/gadget/udc/max3420_udc.c    |   15 +++++----------
>  drivers/usb/host/max3421-hcd.c          |    3 +--
>  kernel/softirq.c                        |    2 +-
>  4 files changed, 9 insertions(+), 17 deletions(-)

For USB stuff:

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>