linux-kernel - Re: [PATCH] Revert "usb: core: remove local_irq

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Message-ID: <20190612144747.mf7hwunsl2zi3uxo@linutronix.de>
Date:   Wed, 12 Jun 2019 16:47:47 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Soeren Moch <smoch@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, tglx@...utronix.de
Subject: Re: [PATCH] Revert "usb: core: remove local_irq_save() around
 ->complete() handler"

On 2019-06-12 10:38:11 [-0400], Alan Stern wrote:
> > 
> > When stopping hostapd after it hangs:
> > [  903.504475] ieee80211 phy0: rt2x00queue_flush_queue: Warning - Queue
> > 14 failed to flush
> 
> Instead of reverting the original commit, can you prevent the problem 
> by adding local_irq_save() and local_irq_restore() to the URB 
> completion routines in that wireless driver?
> 
> Probably people who aren't already pretty familiar with the driver code
> won't easily be able to locate the race.  Still, a little overkill may
> be an acceptable solution.

Not from RT point of view because you do
	local_irq_save() -> spin_lock()

but it might be worth checking if the local_irq_save() within that
wireless driver avoids the race or not.

> Alan Stern

Sebastian