linux-kernel - Re: [PATCH] Drivers: hv: vmbus: Add mutex lock to channel show functions

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Message-ID: <20190215022747.GA53910@ubu-Virtual-Machine>
Date:   Thu, 14 Feb 2019 21:27:47 -0500
From:   Kimberly Brown <kimbrownkd@...il.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     Dexuan Cui <decui@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Long Li <longli@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Drivers: hv: vmbus: Add mutex lock to channel show
 functions

On Thu, Feb 14, 2019 at 08:54:31PM -0500, Sasha Levin wrote:
> On Sat, Feb 02, 2019 at 03:07:35PM -0500, Kimberly Brown wrote:
> > On Fri, Feb 01, 2019 at 06:24:24PM +0000, Dexuan Cui wrote:
> > > > From: Kimberly Brown <kimbrownkd@...il.com>
> > > > Sent: Thursday, January 31, 2019 9:47 AM
> > > > ...
> > > > 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.
> > > Hi Kim,
> > > Can you please share more details about the deadlock?
> > > It's unclear to me how the deadlock happens.
> > > 
> > 
> > Hi Dexuan,
> > 
> > I encountered the deadlock by:
> > 1) Adding a call to msleep() before acquiring the mutex in
> > vmbus_chan_attr_show()
> > 2) Opening a hv_netvsc subchannel's sysfs file
> > 3) Removing hv_netvsc while the sysfs file is opening
> 
> Dexuan, any objections to pulling this fix in?
> 

Hi Sasha,

This fix can cause a deadlock. I'm working on a different fix for the
original race condition problem.

Thanks,
Kim

> --
> Thanks,
> Sasha