21.07.2015 17:22, Oliver Neukum пишет:
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 is
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 2001
From: Oliver Neukum <oneu...@suse.com>
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 <oneu...@suse.com>
---
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 = netdev_priv(net);
struct driver_info *info = 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 = !test_and_clear_bit(EVENT_NO_RUNTIME_PM, &dev->flags);
Right, I missed that. Indeed, if one needs EVENT_NO_RUNTIME_PM bit, one
should get it before dev->flags is set to 0.
dev->flags = 0;
I suppose usbnet_bh() cannot be re-scheduled at this point. And if it is
running now, tasklet_kill will wait till it finishes. So, I guess, it
would be enough to zero dev->flags after "tasklet_kill (&dev->bh);"
rather than before it, like it is now.
Anyway, if it is needed to clear any particular flags to prevent
re-scheduling of usbnet_bh(), this can be done here with clear_bit().
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 touch
EVENT_NO_RUNTIME_PM bit explicitly and these bit operations are atomic
w.r.t. each other.
+ mpn |= !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 = 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
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