Re: [fsdax xfs] Regression panic at inode_switch_wbs_work_fn

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Jul 16, 2021 at 01:13:05PM -0700, Roman Gushchin wrote:
> On Fri, Jul 16, 2021 at 01:57:55PM +0800, Murphy Zhou wrote:
> > Hi,
> > 
> > On Fri, Jul 16, 2021 at 12:07 AM Roman Gushchin <guro@fb.com> wrote:
> > >
> > > On Thu, Jul 15, 2021 at 06:10:22PM +0800, Murphy Zhou wrote:
> > > > Hi,
> > > >
> > > > #Looping generic/270 of xfstests[1] on pmem ramdisk with
> > > > mount option:  -o dax=always
> > > > mkfs.xfs option: -f -b size=4096 -m reflink=0
> > > > can hit this panic now.
> > > >
> > > > #It's not reproducible on ext4.
> > > > #It's not reproducible without dax=always.
> > >
> > > Hi Murphy!
> > >
> > > Thank you for the report!
> > >
> > > Can you, please, check if the following patch fixes the problem?
> > 
> > No. Still the same panic.
> 
> Hm, can you, please, double check this? It seems that the patch fixes the
> problem for others (of course, it can be a different problem).
> CCed you on the proper patch, just sent to the list.
> 
> Otherwise, can you, please, say on which line of code the panic happens?
> (using addr2line utility, for example)

I experience the same problem that Murphy does, and I tracked it down
to this chunk of inode_do_switch_wbs:

	/*
	 * Count and transfer stats.  Note that PAGECACHE_TAG_DIRTY points
	 * to possibly dirty pages while PAGECACHE_TAG_WRITEBACK points to
	 * pages actually under writeback.
	 */
	xas_for_each_marked(&xas, page, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
here >>>>>>>>>> if (PageDirty(page)) {
			dec_wb_stat(old_wb, WB_RECLAIMABLE);
			inc_wb_stat(new_wb, WB_RECLAIMABLE);
		}
	}

I suspect that "page" is really a pfn to a pmem mapping and not a real
struct page.

--D

> 
> Thank you!