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

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Message-ID: <20110518080731.GA2759@infradead.org>
Date:	Wed, 18 May 2011 04:07:31 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, sandeen@...hat.com
Subject: Re: [PATCH 3/3] ext4: Block mmapped writes while the fs is frozen

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.

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