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)?
