From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eugene Shatokhin Subject: Re: Several races in "usbnet" module (kernel 4.1.x) Date: Wed, 22 Jul 2015 21:33:52 +0300 Message-ID: <55AFE210.7030104@rosalab.ru> References: <55AD3A41.2040100@rosalab.ru> <1437488529.3823.16.camel@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netdev@vger.kernel.org, linux-usb@vger.kernel.org, LKML To: Oliver Neukum Return-path: In-Reply-To: <1437488529.3823.16.camel@suse.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 21.07.2015 17:22, Oliver Neukum =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > On Mon, 2015-07-20 at 21:13 +0300, Eugene Shatokhin wrote: >> And here, the code clears EVENT_RX_KILL bit in dev->flags, which may >> execute concurrently with the above operation: >> #0 clear_bit (bitops.h:113, inlined) >> #1 usbnet_bh (usbnet.c:1475) >> /* restart RX again after disabling due to high error rate = */ >> clear_bit(EVENT_RX_KILL, &dev->flags); >> >> If clear_bit() is atomic w.r.t. setting dev->flags to 0, this race i= s >> not a problem, I guess. Otherwise, it may be. > > clear_bit is atomic with respect to other atomic operations. > So how about this: > > Regards > Oliver > Thanks for the quick replies! My comments are below. >>>From 1c4e685b3a9c183e04c46b661830e5c7ed35b513 Mon Sep 17 00:00:00 200= 1 > From: Oliver Neukum > Date: Tue, 21 Jul 2015 16:19:40 +0200 > Subject: [PATCH] usbnet: fix race between usbnet_stop() and the BH > > Does this do the job? > > Signed-off-by: Oliver Neukum > --- > drivers/net/usb/usbnet.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c > index 3c86b10..77a9a86 100644 > --- a/drivers/net/usb/usbnet.c > +++ b/drivers/net/usb/usbnet.c > @@ -778,7 +778,7 @@ int usbnet_stop (struct net_device *net) > { > struct usbnet *dev =3D netdev_priv(net); > struct driver_info *info =3D dev->driver_info; > - int retval, pm; > + int retval, pm, mpn; > > clear_bit(EVENT_DEV_OPEN, &dev->flags); > netif_stop_queue (net); > @@ -813,14 +813,17 @@ int usbnet_stop (struct net_device *net) > * can't flush_scheduled_work() until we drop rtnl (later), > * else workers could deadlock; so make workers a NOP. > */ > + mpn =3D !test_and_clear_bit(EVENT_NO_RUNTIME_PM, &dev->flags); Right, I missed that. Indeed, if one needs EVENT_NO_RUNTIME_PM bit, one= =20 should get it before dev->flags is set to 0. > dev->flags =3D 0; I suppose usbnet_bh() cannot be re-scheduled at this point. And if it i= s=20 running now, tasklet_kill will wait till it finishes. So, I guess, it=20 would be enough to zero dev->flags after "tasklet_kill (&dev->bh);"=20 rather than before it, like it is now. Anyway, if it is needed to clear any particular flags to prevent=20 re-scheduling of usbnet_bh(), this can be done here with clear_bit().=20 Not sure if there are such flags, I am by no means an expert in usbnet. > del_timer_sync (&dev->delay); > tasklet_kill (&dev->bh); The following part is not necessary, I think. usbnet_bh() does not touc= h=20 EVENT_NO_RUNTIME_PM bit explicitly and these bit operations are atomic=20 w.r.t. each other. > + mpn |=3D !test_and_clear_bit(EVENT_NO_RUNTIME_PM, &dev->flags); > + /* in case the bh reset a flag */ But zeroing dev->flags here is necessary, I agree. > + dev->flags =3D 0; > if (!pm) > usb_autopm_put_interface(dev->intf); > > - if (info->manage_power && > - !test_and_clear_bit(EVENT_NO_RUNTIME_PM, &dev->flags)) > + if (info->manage_power && mpn) > info->manage_power(dev, 0); > else > usb_autopm_put_interface(dev->intf); > Regards, Eugene