linux-kernel - Re: [PATCH] VFS: br_write_lock locks on possible CPUs other than online CPUs

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Message-ID: <4EF03B48.6000006@linux.vnet.ibm.com>
Date:	Tue, 20 Dec 2011 13:07:44 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	mc@...ux.vnet.ibm.com
CC:	Al Viro <viro@...IV.linux.org.uk>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Nick Piggin <npiggin@...nel.dk>, david@...morbit.com,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Maciej Rutecki <maciej.rutecki@...il.com>
Subject: Re: [PATCH] VFS: br_write_lock locks on possible CPUs other than
 online CPUs

On 12/20/2011 01:00 PM, mengcong wrote:

> On Tue, 2011-12-20 at 06:27 +0000, Al Viro wrote:
>> On Tue, Dec 20, 2011 at 10:26:05AM +0530, Srivatsa S. Bhat wrote:
>>> Oh, right, that has to be handled as well...
>>>
>>> Hmmm... How about registering a CPU hotplug notifier callback during lock init
>>> time, and then for every cpu that gets onlined (after we took a copy of the
>>> cpu_online_mask to work with), we see if that cpu is different from the ones
>>> we have already locked, and if it is, we lock it in the callback handler and
>>> update the locked_cpu_mask appropriately (so that we release the locks properly
>>> during the unlock operation).
>>>
>>> Handling the newly introduced race between the callback handler and lock-unlock
>>> code must not be difficult, I believe..
>>>
>>> Any loopholes in this approach? Or is the additional complexity just not worth
>>> it here?
>>
>> To summarize the modified variant of that approach hashed out on IRC:
>>
> On which IRC do you discuss?


#kernel on tinc.sekrit.org :-)

Regards,
Srivatsa S. Bhat

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