On Thu, Sep 30, 2021 at 9:49 AM Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > On Thu, 30 Sep 2021, Matthew Wilcox wrote: > > On Wed, Sep 29, 2021 at 10:24:44PM -0700, Hugh Dickins wrote: > > > > > > Aside from the above page->index mischeck in find_lock_entries(), > > > I now think this bug needs nothing more than simply removing the > > > VM_BUG_ON_PAGE(PageTail(page), page) from truncate_inode_page(). > > > > I don't think that's right. This bug was also observed when calling > > truncate(), so there's clearly a situation where two concurrent calls > > to truncate_pagecache() leaves a THP in the cache. > > I assume you're thinking of one of the fuzzer blkdev ones: > https://lore.kernel.org/linux-mm/CACkBjsbtF_peC7N_4mRfHML_BeiPe+O9DahTfr84puSG_J9rcQ@xxxxxxxxxxxxxx/ > or > https://lore.kernel.org/lkml/CACkBjsYwLYLRmX8GpsDpMthagWOjWWrNxqY6ZLNQVr6yx+f5vA@xxxxxxxxxxxxxx/ > > I haven't started on those ones yet: yes, I imagine one or both of those > will need a further fix (S_ISREG() check somewhere if we're lucky; but > could well be nastier); but for the bug in this thread, I expect Makes sense to me. We should be able to check S_ISREG() in khugepaged, if it is not a regular file, just bail out. Sounds not that nasty to me AFAIU. > removing the VM_BUG_ON_PAGE(PageTail) to be enough. > > If you're thinking of something else, please send a link if you can - thanks. > > Hugh >
