Re: Kernel bug: Bad page state: related to generic symlink code and mmap

["Mika Penttilä" <mika.penttila@kolumbus.fi>]

Al Viro wrote:

>On Fri, Aug 19, 2005 at 05:53:32PM +0100, Al Viro wrote:
>  
>
>>I'm taking NFS helpers to libfs.c and switching ncpfs to them.  IMO that's
>>better than copying the damn thing and other network filesystems might have
>>the same needs eventually...
>>    
>>
>
>[something like this - completely untested]
>
>* stray_page_get_link(inode, filler) - returns ERR_PTR(error) or pointer
>to symlink body.  Said symlink body sits in a page at offset equal to
>offsetof(page, struct stray_page_link).  filler() is expected to put it
>at such offset. Page is cached.
>
>* stray_page_put_link() - ->put_link() suitable for links obtained from
>stray_page_get_link().  Unlike the usual pagecache-based variants, this
>sucker does _not_ rely on page staying cached.
>
>* nfs and ncpfs switched to the helpers above.
>
>Signed-off-by: Al Viro <viro@parcelfarce.linux.theplanet.co.uk>
>----
>  
>

Just out of curiosity - what protects even local filesystems against 
concurrent truncate and symlink resolving when using the page cache helpers?

--Mika