linux-ext4 - Re: [PATCH] ext4: fix a bug in ext4_wait_for_tail_page

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Date:   Wed, 18 Sep 2019 09:47:24 +0800
From:   yangerkun <yangerkun@...wei.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>
CC:     <jack@...e.cz>, <linux-ext4@...r.kernel.org>,
        <yi.zhang@...wei.com>, <houtao1@...wei.com>
Subject: Re: [PATCH] ext4: fix a bug in ext4_wait_for_tail_page_commit


On 2019/9/17 23:31, Theodore Y. Ts'o wrote:
> On Tue, Sep 17, 2019 at 04:48:14PM +0800, yangerkun wrote:
>> No need to wait when offset equals to 0. And it will trigger a bug since
>> the latter __ext4_journalled_invalidatepage can free the buffers but leave
>> page still dirty.
> That's only true if the block size == the page size, no?  If the
> offset is zero and the block size is 1k, we still need to wait.
> Shouldn't the better fix be:
>
>> -	if (offset > PAGE_SIZE - i_blocksize(inode))
>> +	if (offset >= PAGE_SIZE - i_blocksize(inode))

It can trigger free buffers in 
__ext4_journalled_invalidatepage(offset==0,blocksize=1k), and we will 
see the bug again.

For some other case, like offset==3k blocksize=1k, actually we should 
wait the commit, but now we will return directly.

Thanks.

>    	   	      		- Ted
>
> .
>