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From: Michael Kelley <mikelley@microsoft.com>
To: kimbrownkd <kimbrownkd@gmail.com>,
	Stephen Hemminger <stephen@networkplumber.org>
Cc: 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, 21 Mar 2019 16:04:20 +0000	[thread overview]
Message-ID: <DM5PR2101MB091851BC7C55093D388514D9D7420@DM5PR2101MB0918.namprd21.prod.outlook.com> (raw)
In-Reply-To: <20190321034752.GA6828@ubu-Virtual-Machine>

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?
> 
> 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

  reply	other threads:[~2019-03-21 16:04 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 [this message]
2019-03-28  4:30                 ` Kimberly Brown
2019-03-28 18:42                   ` Stephen Hemminger
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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