Re: [patch|rfc] block: don't mark buffers beyond end of disk as mapped

[Jeff Moyer]

Nick Piggin <npiggin@xxxxxxxxx> writes:

> On 2 May 2012 00:08, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
>> Nick Piggin <npiggin@xxxxxxxxx> writes:
>>
>>> Not a bad fix. But it's kind of sad to have i_size checking logic also in
>>> block_read_full_page, that does not cope with this.
>>>
>>> I have found there are parts of the kernel (readahead) that try to read
>>> beyond EOF and seem to get angry if we return an error (by not
>>> marking uptodate in readpage) in that case though :(
>>>
>>> But, either way, I think it's very reasonable to not mark buffers beyond
>>> end of device as mapped. So I think your patch is fine.
>>>
>>> I guess for ext[234], it does not read metadata close to the end of the
>>> device or you were using 4K sized blocks?
>>
>> Well, the test case just reads directly from the loop device, bypassing
>> the file system, and I did use 1KB blocks when making the file system, so
>> it is quite puzzling.
>
> It's because buffer_head creation does not go through the same paths
> for bdev file access versus getblk APIs.
>
> blkdev_get_block does the right thing there
>
> In fact, it's probably good to unify the checks here, i.e., use max_blocks()

You really think it's worth it?  I mean, it's just an i_size_read and a
shift, and there is precedent for it inside fs/buffer.c.  I'd prefer to
keep the patch as-is, but will change it if you feel that strongly about
it.

Cheers,
Jeff
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/