From: Stephen Hemminger <stephen@networkplumber.org>
To: Kimberly Brown <kimbrownkd@gmail.com>
Cc: Michael Kelley <mikelley@microsoft.com>,
Long Li <longli@microsoft.com>,
Sasha Levin <Alexander.Levin@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
Dexuan Cui <decui@microsoft.com>,
KY Srinivasan <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 3/3] Drivers: hv: vmbus: Fix race condition with new ring_buffer_info mutex
Date: Thu, 28 Mar 2019 11:42:52 -0700 [thread overview]
Message-ID: <20190328114252.141bbcd5@shemminger-XPS-13-9360> (raw)
In-Reply-To: <20190328043057.GA2258@ubu-Virtual-Machine>
On Thu, 28 Mar 2019 00:30:57 -0400
Kimberly Brown <kimbrownkd@gmail.com> wrote:
> On Thu, Mar 21, 2019 at 04:04:20PM +0000, Michael Kelley wrote:
> > From: Kimberly Brown <kimbrownkd@gmail.com> Sent: Wednesday, March 20, 2019 8:48 PM
> > > > > > Adding more locks will solve the problem but it seems like overkill.
> > > > > > Why not either use a reference count or an RCU style access for the
> > > > > > ring buffer?
> > > > >
> > > > > I agree that a reference count or RCU could also solve this problem.
> > > > > Using mutex locks seemed like the most straightforward solution, but
> > > > > I'll certainly switch to a different approach if it's better!
> > > > >
> > > > > Are you concerned about the extra memory required for the mutex locks,
> > > > > read performance, or something else?
> > > >
> > > > Locks in control path are ok, but my concern is performance of the
> > > > data path which puts packets in/out of rings. To keep reasonable performance,
> > > > no additional locking should be added in those paths.
> > > >
> > > > So if data path is using RCU, can/should the control operations also
> > > > use it?
> > >
>
>
> Hi Stephen,
>
> Do you have any additional questions or suggestions for this race
> condition and the mutex locks? I think that your initial questions were
> addressed in the responses below. If there's anything else, please let
> me know!
>
> Thanks,
> Kim
>
>
> > > The data path doesn't use RCU to protect the ring buffers.
> >
> > My $.02: The mutex is obtained only in the sysfs path and the "delete
> > ringbuffers" path, neither of which is performance or concurrency sensitive.
> > There's no change to any path that reads or writes data from/to the ring
> > buffers. It seems like the mutex is the most straightforward solution to
> > preventing sysfs from accessing the ring buffer info while the memory is
> > being freed as part of "delete ringbuffers".
> >
> > Michael
I have no problems with the patch you did.
My discussion was more around the general issues with ringbuffers being detached
from the device. Not sure if it was even a good design choice but that is
something that is hard to fix now.
next prev parent reply other threads:[~2019-03-28 18:42 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-22 2:07 [PATCH] Drivers: hv: vmbus: Add mutex lock to channel show functions Kimberly Brown
2019-01-22 3:46 ` Dexuan Cui
2019-01-22 6:42 ` Kimberly Brown
2019-01-22 18:40 ` Dexuan Cui
2019-01-28 19:58 ` Kimberly Brown
2019-01-29 19:20 ` Dexuan Cui
2019-01-31 15:19 ` Sasha Levin
2019-01-31 16:45 ` Michael Kelley
2019-01-31 17:47 ` Kimberly Brown
2019-02-01 14:13 ` Sasha Levin
2019-02-01 18:24 ` Dexuan Cui
2019-02-02 20:07 ` Kimberly Brown
2019-02-15 1:54 ` Sasha Levin
2019-02-15 2:27 ` Kimberly Brown
2019-02-22 3:46 ` [PATCH v2 0/2] Fix a race condition vulnerability in "_show" functions Kimberly Brown
2019-02-22 3:47 ` [PATCH v2 1/2] Drivers: hv: vmbus: Refactor chan->state if statement Kimberly Brown
2019-02-24 16:54 ` Michael Kelley
2019-02-22 3:47 ` [PATCH v2 2/2] Drivers: hv: vmbus: Add a channel ring buffer mutex lock Kimberly Brown
2019-02-24 16:53 ` Michael Kelley
2019-02-26 6:24 ` Kimberly Brown
2019-03-14 20:04 ` [PATCH v3 0/3] Drivers: hv: vmbus: Fix a race condition in "_show" functions Kimberly Brown
2019-03-14 20:05 ` [PATCH v3 1/3] Drivers: hv: vmbus: Refactor chan->state if statement Kimberly Brown
2019-03-14 20:05 ` [PATCH v3 2/3] Drivers: hv: vmbus: Set ring_info field to 0 and remove memset Kimberly Brown
2019-03-29 16:01 ` Michael Kelley
2019-03-14 20:05 ` [PATCH v3 3/3] Drivers: hv: vmbus: Fix race condition with new ring_buffer_info mutex Kimberly Brown
2019-03-14 22:45 ` Stephen Hemminger
2019-03-17 1:49 ` Kimberly Brown
2019-03-20 20:06 ` Stephen Hemminger
2019-03-21 3:47 ` Kimberly Brown
2019-03-21 16:04 ` Michael Kelley
2019-03-28 4:30 ` Kimberly Brown
2019-03-28 18:42 ` Stephen Hemminger [this message]
2019-03-29 16:04 ` Michael Kelley
2019-04-10 22:59 ` [PATCH v3 0/3] Drivers: hv: vmbus: Fix a race condition in "_show" functions Sasha Levin
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