From: Andrew Cooper <andrew.cooper3@citrix.com>
To: "Jan Beulich" <jbeulich@suse.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH 2/2] smp: convert cpu_hotplug_begin into a blocking lock acquisition
Date: Wed, 19 Feb 2020 14:58:08 +0000 [thread overview]
Message-ID: <028f4317-7555-218a-c833-b36300a11b8f@citrix.com> (raw)
In-Reply-To: <960b4da8-4522-082a-42b9-ab870698a5ec@suse.com>
On 19/02/2020 13:44, Jan Beulich wrote:
> On 19.02.2020 14:22, Roger Pau Monné wrote:
>> On Wed, Feb 19, 2020 at 01:59:51PM +0100, Jan Beulich wrote:
>>> On 13.02.2020 12:32, Roger Pau Monne wrote:
>>>> Don't allow cpu_hotplug_begin to fail by converting the trylock into a
>>>> blocking lock acquisition. Write users of the cpu_add_remove_lock are
>>>> limited to CPU plug/unplug operations, and cannot deadlock between
>>>> themselves or other users taking the lock in read mode as
>>>> cpu_add_remove_lock is always locked with interrupts enabled. There
>>>> are also no other locks taken during the plug/unplug operations.
>>> I don't think the goal was deadlock avoidance, but rather limiting
>>> of the time spent spinning while trying to acquire the lock, in
>>> favor of having the caller retry.
>> Now that the contention between read-only users is reduced as those
>> can take the lock in parallel I think it's safe to switch writers to
>> blocking mode.
> I'd agree if writers couldn't be starved by (many) readers.
XSA-114.
We fixed that vulnerability ages ago.
A writer wanting the lock will prevent further readers from taking it
before the writer drops it.
~Andrew
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next prev parent reply other threads:[~2020-02-19 14:58 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-13 11:32 [Xen-devel] [PATCH 0/2] smp: convert cpu_add_remove_lock int a rw lock Roger Pau Monne
2020-02-13 11:32 ` [Xen-devel] [PATCH 1/2] smp: convert the cpu maps lock into " Roger Pau Monne
2020-02-19 12:08 ` Julien Grall
2020-02-19 12:56 ` Jan Beulich
2020-02-19 13:19 ` Roger Pau Monné
2020-02-19 13:42 ` Jan Beulich
2020-02-19 14:38 ` Roger Pau Monné
2020-02-20 8:13 ` Jan Beulich
2020-02-20 8:27 ` Jürgen Groß
2020-02-20 8:36 ` Jan Beulich
2020-02-20 8:57 ` Julien Grall
2020-02-20 9:20 ` Roger Pau Monné
2020-02-13 11:32 ` [Xen-devel] [PATCH 2/2] smp: convert cpu_hotplug_begin into a blocking lock acquisition Roger Pau Monne
2020-02-19 12:59 ` Jan Beulich
2020-02-19 13:22 ` Roger Pau Monné
2020-02-19 13:44 ` Jan Beulich
2020-02-19 14:45 ` Roger Pau Monné
2020-02-19 14:57 ` Jan Beulich
2020-02-19 15:07 ` Andrew Cooper
2020-02-19 16:06 ` Jan Beulich
2020-02-19 16:26 ` Roger Pau Monné
2020-02-19 17:06 ` Jan Beulich
2020-02-19 16:54 ` Andrew Cooper
2020-02-19 16:08 ` Roger Pau Monné
2020-02-19 17:03 ` Jan Beulich
2020-02-20 8:16 ` Jan Beulich
2020-02-21 10:23 ` Roger Pau Monné
2020-02-21 13:06 ` Jan Beulich
2020-02-19 14:58 ` Andrew Cooper [this message]
2020-02-19 12:22 ` [Xen-devel] [PATCH 0/2] smp: convert cpu_add_remove_lock int a rw lock Andrew Cooper
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