> On Nov 5, 2019, at 8:58 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Sat, 19 Oct 2019 05:24:00 +0000 Song Liu <songliubraving@xxxxxx> wrote: > >>> We don't have a ref on that page. After we've released the xarray lock >>> we have no business playing with *page at all, correct? >> >> Yeah, this piece is not just redundant, but also buggy. I am also >> including some information about it. >> >> Updated commit log: >> >> ============================= 8< ============================= >> >> In collapse_file(), for !is_shmem case, current check cannot guarantee >> the locked page is up-to-date. Specifically, xas_unlock_irq() should not >> be called before lock_page() and get_page(); and it is necessary to >> recheck PageUptodate() after locking the page. >> >> With this bug and CONFIG_READ_ONLY_THP_FOR_FS=y, madvise(HUGE)'ed .text >> may contain corrupted data. This is because khugepaged mistakenly >> collapses some not up-to-date sub pages into a huge page, and assumes the >> huge page is up-to-date. This will NOT corrupt data in the disk, because >> the page is read-only and never written back. Fix this by properly >> checking PageUptodate() after locking the page. This check replaces >> "VM_BUG_ON_PAGE(!PageUptodate(page), page);". >> >> Also, move PageDirty() check after locking the page. Current khugepaged >> should not try to collapse dirty file THP, because it is limited to >> read-only .text. Add a warning with the PageDirty() check as it should >> not happen. This warning is added after page_mapping() check, because >> if the page is truncated, it might be dirty. > > I've lost the plot on this patch. I have the v3 patch plus these fixes: > > http://lkml.kernel.org/r/20191028221414.3685035-1-songliubraving@xxxxxx > http://lkml.kernel.org/r/20191022191006.411277-1-songliubraving@xxxxxx > http://lkml.kernel.org/r/20191030200736.3455046-1-songliubraving@xxxxxx > > and there's a v4 which I can't correlate with the above. And there has > been discussion about deferring some of the filemap_flush() changes > until later. > > So I think it's best if we just start again. Can you please prepare > and send out a v5 (which might be a 2-patch series)? Sounds good. Sending v5 soon. Thanks, Song
