lkml.org 
[lkml]   [2007]   [Mar]   [19]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
/
DateMon, 19 Mar 2007 21:28:00 +1100
FromNick Piggin <>
SubjectRe: [PATCH 1 of 2] block_page_mkwrite() Implementation V2
Nick Piggin wrote:
> David Chinner wrote:> >> On Mon, Mar 19, 2007 at 05:37:03PM +1100, Nick Piggin wrote:
>>>>> David Chinner wrote:>>>> >>>> +block_page_mkwrite(struct vm_area_struct *vma, struct page *page,
>>>> +           get_block_t get_block)>>>> +{>>>> +    struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
>>>> +    unsigned long end;>>>> +    loff_t size;>>>> +    int ret = -EINVAL;>>>> +>>>> +    lock_page(page);>>>> +    size = i_size_read(inode);>>>> +    if ((page->mapping != inode->i_mapping) ||
>>>> +        ((page->index << PAGE_CACHE_SHIFT) > size)) {
>>>> +        /* page got truncated out from underneath us */
>>>> +        goto out_unlock;
>>>> +    }>>>>>>>>> I see your explanation above, but I still don't see why this can't
>>> just follow the conventional if (!page->mapping) check for truncation.
>>> If the test happens to be performed after truncate concurrently
>>> decreases i_size, then the blocks are going to get truncated by the
>>> truncate afterwards anyway.>>>>>>>> We have to read the inode size in the normal case so that we know if
>> the page is at EOF and is a partial page so we don't allocate past EOF in
>> block_prepare_write().  Hence it seems like a no-brainer to me to check
>> and error out on a page that we *know* is beyond EOF.
>>>> I can drop the check if you see no value in it - I just don't
>> like the idea of ignoring obvious boundary condition violations...> > > I would prefer it dropped, to be honest. I can see how the check does
> pick up that corner case, however truncate is difficult enough (at
> least, it has been an endless source of problems) that we want to keep
> everyone else simple and have all the non-trivial stuff in truncate.
> 

Hmm, actually on second thoughts it probably is reasonable to recheck
i_size under the page lock... we need to do similar in the nopage path
to close the nopage vs invalidate race.

However, the already-truncated test I think can just be !page->mapping:
there should be no way for the page mapping to change to something
other than NULL.

-- 
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com 

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

\
 
 \ /
  Last update: 2007-03-19 11:31    [from the cache]
©2003-2008