On Thu, Jul 18, 2019 at 07:53:42PM -0700, Dan Williams wrote:
[ add Sasha for -stable advice ]
On Thu, Jul 18, 2019 at 5:13 PM Liu Bo bo.liu@linux.alibaba.com wrote:
The livelock can be triggerred in the following pattern,
while (index < end && pagevec_lookup_entries(&pvec, mapping, index, min(end - index, (pgoff_t)PAGEVEC_SIZE), indices)) { ... for (i = 0; i < pagevec_count(&pvec); i++) { index = indices[i]; ... } index++; /* BUG */ }multi order exceptional entry is not specially considered in invalidate_inode_pages2_range() and it ended up with a livelock because both index 0 and index 1 finds the same pmd, but this pmd is binded to index 0, so index is set to 0 again.
This introduces a helper to take the pmd entry's length into account when deciding the next index.
Note that there're other users of the above pattern which doesn't need to fix,
- dax_layout_busy_page
It's been fixed in commit d7782145e1ad ("filesystem-dax: Fix dax_layout_busy_page() livelock")
- truncate_inode_pages_range
This won't loop forever since the exceptional entries are immediately removed from radix tree after the search.
Fixes: 642261a ("dax: add struct iomap based DAX PMD support") Cc: stable@vger.kernel.org since 4.9 to 4.19 Signed-off-by: Liu Bo bo.liu@linux.alibaba.com
The problem is gone after commit f280bf092d48 ("page cache: Convert find_get_entries to XArray"), but since xarray seems too new to backport to 4.19, I made this fix based on radix tree implementation.
I think in this situation, since mainline does not need this change and the bug has been buried under a major refactoring, is to send a backport directly against the v4.19 kernel. Include notes about how it replaces the fix that was inadvertently contained in f280bf092d48 ("page cache: Convert find_get_entries to XArray"). Do you have a test case that you can include in the changelog?
The root cause behind the bug is exactly same as what commit d7782145e1ad ("filesystem-dax: Fix dax_layout_busy_page() livelock") does.
For test case, I have a not 100% reproducible one based on ltp's rwtest[1] and virtiofs.
[1]: $mount -t virtio_fs -o tag=alwaysdax -o rootmode=040000,user_id=0,group_id=0,dax,default_permissions,allow_other alwaysdax /mnt/virtio-fs/ $cat test.txt rwtest01 export LTPROOT; rwtest -N rwtest01 -c -q -i 60s -f sync 10%25000:$TMPDIR/rw-sync-$$ $runltp -d /mnt/virtio-fs -f test.txt
thanks, -liubo