Re: [PATCH] VFS readahead bug in 2.6.8-rc[1-3]

[Phillip Lougher <phillip@lougher.demon.co.uk>]

Nick Piggin wrote:
> Phillip Lougher wrote:
> 
>> Nick Piggin wrote:
>>
>>> On second thought, maybe not. I think your filesystem is at fault.
>>
>>
>>
>> No I'm not wrong here. With a read-only filesystem i_size can
>> never change, there are no possible race conditions.  If a too
>> large index is passed it is a VFS bug.  Are you suggesting I should
>> start to code assuming the VFS is broken?
>>
> 
> No, I suggest you start to code assuming this interface does
> what it does. I didn't say there is no bug here, but nobody
> else's filesystem breaks.
> 

Point one: The interface didn't do this UNTIL you changed the code
Point two: Just because no one has reported other filesystem
breakage, it doesn't mean other filesystems have not broken.

Perhaps I should have the check in my code.  However, it is
still stupid to fix an occasional race by ensuring readpage() is
always called with an out of bounds index when files are 0 or a
4K multiple.  The filesystem check may prevent a crash, but it
is needlessly wasteful by design, not through any inadvertant
race condition.

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