linux-ext4 - Re: [PATCH 3/3] ext4: Block mmapped writes while the fs is frozen

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Message-ID: <4DD3D1AF.9060809@redhat.com>
Date:	Wed, 18 May 2011 09:03:27 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 3/3] ext4: Block mmapped writes while the fs is frozen

On 5/18/11 3:07 AM, Christoph Hellwig wrote:
> On Wed, May 18, 2011 at 09:56:14AM +0200, Jan Kara wrote:
>> __block_page_mkwrite() and return some error value (EAGAIN translating to
>> VM_FAULT_RETRY would look logical, I just have to think off better error
>> value for VM_FAULT_NOPAGE). But vfs_check_frozen() cannot be in
>> __block_page_mkwrite() since ext4 needs to call that with a transaction
>> started so that would create a deadlock and we need to call
>> vfs_check_frozen() somewhere so that we don't busyloop.
>>
>> I can call vfs_check_frozen() inside block_page_mkwrite() but it would be a
>> bit surprising difference from __block_page_mkwrite() to me. Not sure what
>> the cleanest solution would be here...
> 
> block_page_mkwrite is supposed to be used directly by filesystems and
> do all the right things.  IIRC Eric even mentioned he added
> vfs_check_frozen to it for RHEL, but forgot to push it upstream.

Well, I tried, but it was rejected IIRC.  Still, mea culpa....

I can resurrect what I did for RHEL5 and repost if desired...

-Eric
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