linux-kernel - Re: [PATCH 1/2] Add partition resize function to BLKPG ioctl

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Message-ID: <4EFD012D.7040602@cfl.rr.com>
Date:	Thu, 29 Dec 2011 19:09:17 -0500
From:	Phillip Susi <psusi@....rr.com>
To:	Maxim Patlasov <maxim.patlasov@...il.com>
CC:	vgoyal@...hat.com, joe@...ches.com, kzak@...hat.com,
	linux-kernel@...r.kernel.org, jaxboe@...ionio.com
Subject: Re: [PATCH 1/2] Add partition resize function to BLKPG ioctl

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On 12/29/2011 12:06 PM, Maxim Patlasov wrote:
> Phillip,
> 
> The patch seems to have some problems:
> 
> 1. Typo in part_nr_sects_write_begin:
> 
>> +	write_seqcount_begin(&seq);
> 
> It should be write_seqcount_begin(seq). Similar issue in
> part_nr_sects_write_end().
> 
> 2. part_nr_sects_write_begin/end is never called.
> 
> 3. part->seq should be initialized with seqcount_init().
> 
> Btw, do we really need both part_nr_sects_write_begin and
> part_nr_sects_write_end? What about:

Good points.  I also noticed that the read/write functions were only being called when not holding the mutex.  If anyone is touching nr_sects without the mutex, then everyone must use the read/write functions, whether they hold the mutex or not.  Otherwise, a mutex holder that touches it directly will race with a non mutex holder using the seqcounter.  Vivek, rather than fix the rest of the references to nr_sects to use the read/write functions, why not just fix the few sites that were accessing it without the mutex to take the mutex fist instead of using a seqcounter?
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