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From: Johan Hovold <johan@kernel.org>
To: Oliver Neukum <oneukum@suse.com>
Cc: Johan Hovold <johan@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	linux-usb@vger.kernel.org
Subject: [1/5] USB: serial: fix unthrottle races
Date: Mon, 29 Apr 2019 12:03:38 +0200	[thread overview]
Message-ID: <20190429100338.GJ26546@localhost> (raw)

On Mon, Apr 29, 2019 at 11:50:58AM +0200, Oliver Neukum wrote:
> On Do, 2019-04-25 at 18:05 +0200, Johan Hovold wrote:
> > @@ -484,6 +503,12 @@ void usb_serial_generic_unthrottle(struct tty_struct *tty)
> >         port->throttled = port->throttle_req = 0;
> >         spin_unlock_irq(&port->lock);
> >  
> > +       /*
> > +        * Matches the smp_mb__after_atomic() in
> > +        * usb_serial_generic_read_bulk_callback().
> > +        */
> > +       smp_mb();
> > +
> >         if (was_throttled)
> >                 usb_serial_generic_submit_read_urbs(port, GFP_KERNEL);
> 
> 
> Doesn't the spin_unlock_irq() imply smp_mb()?
> Otherwise it looks correct to me.

No, spin_unlock_irq() is only a one-way barrier, and doesn't prevent
later accesses from "moving" into the locked section.

Johan

WARNING: multiple messages have this Message-ID (diff)
From: Johan Hovold <johan@kernel.org>
To: Oliver Neukum <oneukum@suse.com>
Cc: Johan Hovold <johan@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	linux-usb@vger.kernel.org
Subject: Re: [PATCH 1/5] USB: serial: fix unthrottle races
Date: Mon, 29 Apr 2019 12:03:38 +0200	[thread overview]
Message-ID: <20190429100338.GJ26546@localhost> (raw)
Message-ID: <20190429100338.MdKV8_ZYBv2lpxlRQezdWQhDl_5y-SPBCiCh66x8Hdo@z> (raw)
In-Reply-To: <1556531458.20085.8.camel@suse.com>

On Mon, Apr 29, 2019 at 11:50:58AM +0200, Oliver Neukum wrote:
> On Do, 2019-04-25 at 18:05 +0200, Johan Hovold wrote:
> > @@ -484,6 +503,12 @@ void usb_serial_generic_unthrottle(struct tty_struct *tty)
> >         port->throttled = port->throttle_req = 0;
> >         spin_unlock_irq(&port->lock);
> >  
> > +       /*
> > +        * Matches the smp_mb__after_atomic() in
> > +        * usb_serial_generic_read_bulk_callback().
> > +        */
> > +       smp_mb();
> > +
> >         if (was_throttled)
> >                 usb_serial_generic_submit_read_urbs(port, GFP_KERNEL);
> 
> 
> Doesn't the spin_unlock_irq() imply smp_mb()?
> Otherwise it looks correct to me.

No, spin_unlock_irq() is only a one-way barrier, and doesn't prevent
later accesses from "moving" into the locked section.

Johan

         reply	other threads:[~2019-04-29 10:03 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-25 16:05 [PATCH 0/5] USB: fix tty unthrottle races Johan Hovold
2019-04-25 16:05 ` [1/5] USB: serial: fix " Johan Hovold
2019-04-25 16:05   ` [PATCH 1/5] " Johan Hovold
2019-04-29  9:50   ` [1/5] " Oliver Neukum
2019-04-29  9:50     ` [PATCH 1/5] " Oliver Neukum
2019-04-29 10:03     ` Johan Hovold [this message]
2019-04-29 10:03       ` Johan Hovold
2019-05-13 10:43   ` Johan Hovold
2019-05-13 10:56     ` Greg Kroah-Hartman
2019-05-13 11:46       ` Johan Hovold
2019-05-13 12:51         ` Greg Kroah-Hartman
2019-05-13 12:59           ` Johan Hovold
2019-05-14 12:53             ` Sasha Levin
2019-05-14 12:57               ` Johan Hovold
2019-04-25 16:05 ` [2/5] USB: serial: clean up throttle handling Johan Hovold
2019-04-25 16:05   ` [PATCH 2/5] " Johan Hovold
2019-04-25 16:05 ` [3/5] USB: serial: generic: drop unnecessary goto Johan Hovold
2019-04-25 16:05   ` [PATCH 3/5] " Johan Hovold
2019-04-25 16:05 ` [4/5] USB: cdc-acm: fix unthrottle races Johan Hovold
2019-04-25 16:05   ` [PATCH 4/5] " Johan Hovold
2019-04-29 10:09   ` [4/5] " Oliver Neukum
2019-04-29 10:09     ` [PATCH 4/5] " Oliver Neukum
2019-04-25 16:05 ` [5/5] USB: cdc-acm: clean up throttle handling Johan Hovold
2019-04-25 16:05   ` [PATCH 5/5] " Johan Hovold
2019-04-29 10:10   ` [5/5] " Oliver Neukum
2019-04-29 10:10     ` [PATCH 5/5] " Oliver Neukum
2019-04-25 20:58 ` [PATCH 0/5] USB: fix tty unthrottle races Alan Stern
2019-04-26  4:55   ` Johan Hovold
2019-04-29  9:30 ` Johan Hovold

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