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

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Message-ID: <87mz68xoyi.fsf@duaron.myhome.or.jp>
Date:	Fri, 01 Dec 2006 12:41:25 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, linux-fsdevel@...r.kernel.org
Subject: Re: [patch 3/3] fs: fix cont vs deadlock patches

Nick Piggin <npiggin@...e.de> writes:

> On Fri, Dec 01, 2006 at 07:14:28AM +0900, OGAWA Hirofumi wrote:
>> 
>> quick look. Doesn't this break reiserfs? IIRC, the reiserfs is using
>> it for another reason. I was also working for this, but I lost the
>> thread of this, sorry.
>> 
>> I found some another users (affs, hfs, hfsplus). Those seem have same
>> problem, but probably those also can use this...
>> 
>> What do you think?
>> -- 
>> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
>> 
>> 
>> 
>> Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
>> ---
>> 
>>  fs/buffer.c                 |   59 +++++++++++++++++---------------------------
>>  fs/fat/file.c               |    2 -
>>  include/linux/buffer_head.h |    1 
>>  3 files changed, 24 insertions(+), 38 deletions(-)
>> 
>> diff -puN fs/buffer.c~generic_cont_expand-avoid-zero-size fs/buffer.c
>> --- linux-2.6/fs/buffer.c~generic_cont_expand-avoid-zero-size	2006-11-13 01:42:01.000000000 +0900
>> +++ linux-2.6-hirofumi/fs/buffer.c	2006-11-13 02:16:20.000000000 +0900
>> @@ -2004,18 +2004,24 @@ int block_read_full_page(struct page *pa
>>  	return 0;
>>  }
>>  
>> -/* utility function for filesystems that need to do work on expanding
>> +/*
>> + * utility function for filesystems that need to do work on expanding
>>   * truncates.  Uses prepare/commit_write to allow the filesystem to
>>   * deal with the hole.  
>>   */
>> -static int __generic_cont_expand(struct inode *inode, loff_t size,
>> -				 pgoff_t index, unsigned int offset)
>> +int generic_cont_expand(struct inode *inode, loff_t size)
>>  {
>>  	struct address_space *mapping = inode->i_mapping;
>> +	loff_t pos = inode->i_size;
>>  	struct page *page;
>>  	unsigned long limit;
>> +	pgoff_t index;
>> +	unsigned int from, to;
>> +	void *kaddr;
>>  	int err;
>>  
>> +	WARN_ON(pos >= size);
>> +
>>  	err = -EFBIG;
>>          limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
>>  	if (limit != RLIM_INFINITY && size > (loff_t)limit) {
>> @@ -2025,11 +2031,18 @@ static int __generic_cont_expand(struct 
>>  	if (size > inode->i_sb->s_maxbytes)
>>  		goto out;
>>  
>> +	index = (size - 1) >> PAGE_CACHE_SHIFT;
>> +	to = size - ((loff_t)index << PAGE_CACHE_SHIFT);
>> +	if (index != (pos >> PAGE_CACHE_SHIFT))
>> +		from = 0;
>> +	else
>> +		from = pos & (PAGE_CACHE_SIZE - 1);
>> +
>>  	err = -ENOMEM;
>>  	page = grab_cache_page(mapping, index);
>>  	if (!page)
>>  		goto out;
>> -	err = mapping->a_ops->prepare_write(NULL, page, offset, offset);
>> +	err = mapping->a_ops->prepare_write(NULL, page, from, to);
>>  	if (err) {
>>  		/*
>>  		 * ->prepare_write() may have instantiated a few blocks
>> @@ -2041,7 +2054,12 @@ static int __generic_cont_expand(struct 
>>  		goto out;
>>  	}
>>  
>> -	err = mapping->a_ops->commit_write(NULL, page, offset, offset);
>> +	kaddr = kmap_atomic(page, KM_USER0);
>> +	memset(kaddr + from, 0, to - from);
>> +	flush_dcache_page(page);
>> +	kunmap_atomic(kaddr, KM_USER0);
>> +
>> +	err = mapping->a_ops->commit_write(NULL, page, from, to);
>
> So basically this is changing from having prepare_write do all the
> zeroing, to zeroing the last page in generic_cont_expand, so that
> we don't have to pass a zero-length to prepare_write?

Yes, this patch doesn't pass zero-length to prepare_write. However,
I'm not checking this patch is ok for reiserfs...
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
-
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