Re: [BUG] reiser4: page lock recursion in reiser4_write_extent

Vladimir V. Saveliev
2007-03-14T17:01:46Z

Hello

On Wednesday 14 March 2007 08:40, Nate Diller wrote:
> This little code snippet seems to have a page_lock recursion, in
> addition to overall looking particularly fragile to me. It seems to
> be handling the case where a page needs to be brought uptodate because
> a partial page write is being done. The page gets locked as many as 3
> times, each checking PageUptodate, however the two failure cases here
> go BUG() instead of returning an error. I'm starting to think that
> somehow the whole suspect branch just never gets taken, because
> otherwise I would expect to see bug reports related to -EIO, -ENOMEM,
> etc causing this to barf.
>
> either way, it seems there's a lock recursion if another thread races
> to bring @page uptodate while we're waiting on the first lock_page()
> call.
>
> ---
>
> page = jnode_page(jnodes[i]);
> if (page_offset(page) < inode->i_size &&
> !PageUptodate(page) && to_page != PAGE_CACHE_SIZE) {
> /*
> * the above is not optimal for partial write to last
> * page of file when file size is not at boundary of
> * page
> */
> takes the lock
> lock_page(page);
> raced with readpage?
> if (!PageUptodate(page)) {
> readpage drops lock
> result = readpage_unix_file(NULL, page);
> BUG_ON(result != 0);
> -ENOMEM?
> /* wait for read completion */
> lock_page(page);
> BUG_ON(!PageUptodate(page));
> -EIO?
> unlock_page(page);
> } else
> still have the lock here
> result = 0;
> }
>
> BUG_ON(get_current_context()->trans->atom != NULL);
> fault_in_pages_readable(buf, to_page);
> BUG_ON(get_current_context()->trans->atom != NULL);
>
> BOOM!!!
> lock_page(page);
> if (!PageUptodate(page) && to_page != PAGE_CACHE_SIZE) {

you are right, I will make a patch.