linux-kernel - Re: [PATCH v12 2/5] xenbus/backend: Protect xenbus callback with lock

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Message-ID: <af02058a-fa76-5eb5-5c2b-60555273bac2@suse.com>
Date:   Wed, 18 Dec 2019 13:27:37 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     SeongJae Park <sjpark@...zon.com>, axboe@...nel.dk,
        konrad.wilk@...cle.com, roger.pau@...rix.com
Cc:     SeongJae Park <sjpark@...zon.de>, pdurrant@...zon.com,
        sj38.park@...il.com, xen-devel@...ts.xenproject.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 2/5] xenbus/backend: Protect xenbus callback with lock

On 18.12.19 11:42, SeongJae Park wrote:
> From: SeongJae Park <sjpark@...zon.de>
> 
> 'reclaim_memory' callback can race with a driver code as this callback
> will be called from any memory pressure detected context.  To deal with
> the case, this commit adds a spinlock in the 'xenbus_device'.  Whenever
> 'reclaim_memory' callback is called, the lock of the device which passed
> to the callback as its argument is locked.  Thus, drivers registering
> their 'reclaim_memory' callback should protect the data that might race
> with the callback with the lock by themselves.

Any reason you don't take the lock around the .probe() and .remove()
calls of the backend (xenbus_dev_probe() and xenbus_dev_remove())? This
would eliminate the need to do that in each backend instead.


Juergen