linux-kernel - Re: [patch 3/3] fs: fix cont vs deadlock patches

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Message-ID: <4570CA90.8050203@yahoo.com.au>
Date:	Sat, 02 Dec 2006 11:36:32 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
CC:	Nick Piggin <npiggin@...e.de>, Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [patch 3/3] fs: fix cont vs deadlock patches

OGAWA Hirofumi wrote:
> Nick Piggin <npiggin@...e.de> writes:
> 
> 
>>>> 		status = __block_prepare_write(inode, new_page, zerofrom,
>>>> 						PAGE_CACHE_SIZE, get_block);
>>>> 		if (status)
>>>>@@ -2110,7 +2111,7 @@
>>>> 		memset(kaddr+zerofrom, 0, PAGE_CACHE_SIZE-zerofrom);
>>>> 		flush_dcache_page(new_page);
>>>> 		kunmap_atomic(kaddr, KM_USER0);
>>>>-		generic_commit_write(NULL, new_page, zerofrom, PAGE_CACHE_SIZE);
>>>>+		__block_commit_write(inode, new_page, zerofrom, PAGE_CACHE_SIZE);
>>>
>>>Whatever function this is doesn't need to update i_size?
>>
>>Yes, it is the code in cont_prepare_write that is expanding a hole
>>at the end of file.
>>
>>We can do this now because fat_commit_write is now changed to call
>>generic_commit_write in the case of a non-zero length.
>>
>>I think it is an improvement because now the file will not get
>>arbitrarily extended in the case of a write failure somewhere down
>>the track.
> 
> 
> Ah, unfortunately we can't this. If we don't update ->i_size before
> page_cache_release, pdflush will think these pages is outside ->i_size
> and just clean the page without writing it.

I see. I guess you need to synchronise your writepage versus this
extention in order to handle it properly then. I won't bother with
that though: it won't be worse than it was before.

Thanks for review, do you agree with the other hunks?

-- 
SUSE Labs, Novell Inc.
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