All of lore.kernel.org
 help / color / mirror / Atom feed
From: Kimberly Brown <kimbrownkd@gmail.com>
To: Michael Kelley <mikelley@microsoft.com>
Cc: Sasha Levin <sashal@kernel.org>, Dexuan Cui <decui@microsoft.com>,
	Long Li <longli@microsoft.com>,
	Sasha Levin <Alexander.Levin@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	"devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Drivers: hv: vmbus: Add mutex lock to channel show functions
Date: Thu, 31 Jan 2019 12:47:07 -0500	[thread overview]
Message-ID: <20190131174707.GA2055@ubu-Virtual-Machine> (raw)
In-Reply-To: <DM5PR2101MB091847B2B68D7F9F2050CE45D7910@DM5PR2101MB0918.namprd21.prod.outlook.com>

On Thu, Jan 31, 2019 at 04:45:35PM +0000, Michael Kelley wrote:
> From: Sasha Levin <sashal@kernel.org> Sent: Thursday, January 31, 2019 7:20 AM
> > 
> > I've queued this one for hyper-fixes, thanks all!
> > 
> 
> Actually, please hold off on queuing this one.  In a conversation I had yesterday with Kim, they had identified a deadlock.  Kim was going to be looking at some revisions to avoid the deadlock.
> 
> Kim -- please confirm.
> 
> Michael

This is correct. I need to send a v2 of this patch which addresses two
issues:

1) Check channel->state inside the mutex acquire/release in
vmbus_chan_attr_show().

2) Prevent a deadlock that can occur between the proposed mutex_lock()
call in the vmbus_chan_attr_show() function and the sysfs/kernfs functions.


I've identified two possible solutions to the deadlock:

1) Add a new mutex to the vmbus_channel struct which protects changes to
"channel->state". Use this new mutex in vmbus_chan_attr_show() instead of
"vmbus_connection.channel_mutex".

2) Use "vmbus_connection.channel_mutex" in vmbus_chan_attr_show() as
originally proposed, and acquire it with mutex_trylock(). If the mutex
cannot be acquired, return -EINVAL.


I'm leaning towards (2), using mutex_trylock(). "vmbus_connection.channel_mutex"
appears to be used only when a channel is being opened or closed, so
vmbus_chan_attr_show() should be able to acquire the mutex when the
channel is in use.

If anyone has suggestions, please let me know.

Thanks,
Kim

  reply	other threads:[~2019-01-31 17:47 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 [this message]
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
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190131174707.GA2055@ubu-Virtual-Machine \
    --to=kimbrownkd@gmail.com \
    --cc=Alexander.Levin@microsoft.com \
    --cc=decui@microsoft.com \
    --cc=devel@linuxdriverproject.org \
    --cc=haiyangz@microsoft.com \
    --cc=kys@microsoft.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=longli@microsoft.com \
    --cc=mikelley@microsoft.com \
    --cc=sashal@kernel.org \
    --cc=sthemmin@microsoft.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.