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?
Yes, I need a _TON_ of documentation, and signed off by from all of the developers involved in this part of the kernel, before I can take this not-in-mainline patch.
thanks,
greg k-h