On Fri, Jul 03, 2020 at 11:53:25AM +0200, Andreas Gruenbacher wrote:
> So far, gfs2 has taken the inode glocks inside the ->readpage and
> ->readahead address space operations. Since commit d4388340ae0b ("fs:
> convert mpage_readpages to mpage_readahead"), gfs2_readahead is passed
> the pages to read ahead locked. With that, the current holder of the
> inode glock may be trying to lock one of those pages while
> gfs2_readahead is trying to take the inode glock, resulting in a
> deadlock.
>
> Fix that by moving the lock taking to the higher-level ->read_iter file
> and ->fault vm operations. This also gets rid of an ugly lock inversion
> workaround in gfs2_readpage.
>
> Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> -/**
> - * __gfs2_readpage - readpage
> - * @file: The file to read a page for
> - * @page: The page to read
> - *
> - * This is the core of gfs2's readpage. It's used by the internal file
> - * reading code as in that case we already hold the glock. Also it's
> - * called by gfs2_readpage() once the required lock has been granted.
> - */
> -
> static int __gfs2_readpage(void *file, struct page *page)
You could go a little further and rename this function to plain
gfs2_readpage().
gfs2_internal_read() should switch from read_cache_page() to
read_mapping_page().
> {
> struct gfs2_inode *ip = GFS2_I(page->mapping->host);
> struct gfs2_sbd *sdp = GFS2_SB(page->mapping->host);
> -
> int error;
>
> if (i_blocksize(page->mapping->host) == PAGE_SIZE &&
> @@ -505,36 +494,11 @@ static int __gfs2_readpage(void *file, struct page *page)
> * gfs2_readpage - read a page of a file
> * @file: The file to read
> * @page: The page of the file
> - *
> - * This deals with the locking required. We have to unlock and
> - * relock the page in order to get the locking in the right
> - * order.
> */
I'd drop the kernel-doc comments on method implementations entirely,
unless there's something useful to say ... which there isn't any more
(yay!)
> @@ -598,16 +562,9 @@ static void gfs2_readahead(struct readahead_control *rac)
> {
> struct inode *inode = rac->mapping->host;
> struct gfs2_inode *ip = GFS2_I(inode);
> - struct gfs2_holder gh;
>
> - gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &gh);
> - if (gfs2_glock_nq(&gh))
> - goto out_uninit;
> if (!gfs2_is_stuffed(ip))
> mpage_readahead(rac, gfs2_block_map);
I think you probably want to make this:
if (i_blocksize(page->mapping->host) == PAGE_SIZE &&
!page_has_buffers(page))
error = iomap_readahead(rac, &gfs2_iomap_ops);
else if (!gfs2_is_stuffed(ip))
error = mpage_readahead(rac, gfs2_block_map);
... but I understand not wanting to make that change at this point
in the release cycle.
I'm happy for the patches to go in as-is, just wanted to point out these
improvements that could be made.
