[cc: vivek, stefan, dgilbert]
On Fri, Jun 21, 2019 at 12:04 AM Liu Bo <obuil.liubo@xxxxxxxxx> wrote:
>
> On Thu, Jun 20, 2019 at 1:36 AM Jan Kara <jack@xxxxxxx> wrote:
> >
> > [added some relevant lists to CC - this can safe some people debugging by
> > being able to google this discussion]
> >
> > On Wed 19-06-19 15:57:38, Liu Bo wrote:
> > > I found a weird dead loop within invalidate_inode_pages2_range, the
> > > reason being that pagevec_lookup_entries(index=1) returns an indices
> > > array which has only one entry storing value 0, and this has led
> > > invalidate_inode_pages2_range() to a dead loop, something like,
> > >
> > > invalidate_inode_pages2_range()
> > > -> while (pagevec_lookup_entries(index=1, indices))
> > > -> for (i = 0; i < pagevec_count(&pvec); i++) {
> > > -> index = indices[0]; // index is set to 0
> > > -> if (radix_tree_exceptional_entry(page)) {
> > > -> if (!invalidate_exceptional_entry2()) //
> > > ->__dax_invalidate_mapping_entry // return 0
> > > -> // entry marked as PAGECACHE_TAG_DIRTY/TOWRITE
> > > ret = -EBUSY;
> > > ->continue;
> > > } // end of if (radix_tree_exceptional_entry(page))
> > > -> index++; // index is set to 1
> > >
> > > The following debug[1] proved the above analysis, I was wondering if
> > > this was a corner case that pagevec_lookup_entries() allows or a
> > > known bug that has been fixed upstream?
> > >
> > > ps: the kernel in use is 4.19.30 (LTS).
> >
> > Hum, the above trace suggests you are using DAX. Are you really? Because the
> > stacktrace below shows we are working on fuse inode so that shouldn't
> > really be DAX inode...
> >
>
> So I was running tests against virtiofs[1] which adds dax support to
> fuse, with dax, fuse provides posix stuff while dax provides data
> channel.
>
> [1]: https://virtio-fs.gitlab.io/
> https://gitlab.com/virtio-fs/linux
>
> thanks,
> liubo
>
> > Honza
> >
> > > [1]:
> > > $git diff
> > > diff --git a/mm/truncate.c b/mm/truncate.c
> > > index 71b65aab8077..82bfeeb53135 100644
> > > --- a/mm/truncate.c
> > > +++ b/mm/truncate.c
> > > @@ -692,6 +692,7 @@ int invalidate_inode_pages2_range(struct
> > > address_space *mapping,
> > > struct page *page = pvec.pages[i];
> > >
> > > /* We rely upon deletion not changing page->index */
> > > + WARN_ONCE(index > indices[i], "index = %d
> > > indices[%d]=%d\n", index, i, indices[i]);
> > > index = indices[i];
> > > if (index > end)
> > > break;
> > >
> > > [ 129.095383] ------------[ cut here ]------------
> > > [ 129.096164] index = 1 indices[0]=0
> > > [ 129.096786] WARNING: CPU: 0 PID: 3022 at mm/truncate.c:695
> > > invalidate_inode_pages2_range+0x471/0x500
> > > [ 129.098234] Modules linked in:
> > > [ 129.098717] CPU: 0 PID: 3022 Comm: doio Not tainted 4.19.30+ #4
> > > ...
> > > [ 129.101288] RIP: 0010:invalidate_inode_pages2_range+0x471/0x500
> > > ...
> > > [ 129.114162] Call Trace:
> > > [ 129.114623] ? __schedule+0x2ad/0x860
> > > [ 129.115214] ? prepare_to_wait_event+0x80/0x140
> > > [ 129.115903] ? finish_wait+0x3f/0x80
> > > [ 129.116452] ? request_wait_answer+0x13d/0x210
> > > [ 129.117128] ? remove_wait_queue+0x60/0x60
> > > [ 129.117757] ? make_kgid+0x13/0x20
> > > [ 129.118277] ? fuse_change_attributes_common+0x7d/0x130
> > > [ 129.119057] ? fuse_change_attributes+0x8d/0x120
> > > [ 129.119754] fuse_dentry_revalidate+0x2c5/0x300
> > > [ 129.120456] lookup_fast+0x237/0x2b0
> > > [ 129.121018] path_openat+0x15f/0x1380
> > > [ 129.121614] ? generic_update_time+0x6b/0xd0
> > > [ 129.122316] do_filp_open+0x91/0x100
> > > [ 129.122876] do_sys_open+0x126/0x210
> > > [ 129.123453] do_syscall_64+0x55/0x180
> > > [ 129.124036] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > > [ 129.124820] RIP: 0033:0x7fbe0cd75e80
> > > ...
> > > [ 129.134574] ---[ end trace c0fc0bbc5aebf0dc ]---
> > --
> > Jan Kara <jack@xxxxxxxx>
> > SUSE Labs, CR
