On Fri, 7 Jul 2023 14:12:06 -0400 David Wysochanski <dwysocha@xxxxxxxxxx> wrote: > On Fri, Jul 7, 2023 at 12:46 PM Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> wrote: > > > > On Sat, Jul 8, 2023 at 1:39 AM Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> wrote: > > > > > > On Wed, Jun 28, 2023 at 11:48:52AM +0100, David Howells wrote: > > > > Fscache has an optimisation by which reads from the cache are skipped until > > > > we know that (a) there's data there to be read and (b) that data isn't > > > > entirely covered by pages resident in the netfs pagecache. This is done > > > > with two flags manipulated by fscache_note_page_release(): > > > > > > > > if (... > > > > test_bit(FSCACHE_COOKIE_HAVE_DATA, &cookie->flags) && > > > > test_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags)) > > > > clear_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags); > > > > > > > > where the NO_DATA_TO_READ flag causes cachefiles_prepare_read() to indicate > > > > that netfslib should download from the server or clear the page instead. > > > > > > > > The fscache_note_page_release() function is intended to be called from > > > > ->releasepage() - but that only gets called if PG_private or PG_private_2 > > > > is set - and currently the former is at the discretion of the network > > > > filesystem and the latter is only set whilst a page is being written to the > > > > cache, so sometimes we miss clearing the optimisation. > > > > > > > > Fix this by following Willy's suggestion[1] and adding an address_space > > > > flag, AS_RELEASE_ALWAYS, that causes filemap_release_folio() to always call > > > > ->release_folio() if it's set, even if PG_private or PG_private_2 aren't > > > > set. > > > > > > > > Note that this would require folio_test_private() and page_has_private() to > > > > become more complicated. To avoid that, in the places[*] where these are > > > > used to conditionalise calls to filemap_release_folio() and > > > > try_to_release_page(), the tests are removed the those functions just > > > > jumped to unconditionally and the test is performed there. > > > > > > > > [*] There are some exceptions in vmscan.c where the check guards more than > > > > just a call to the releaser. I've added a function, folio_needs_release() > > > > to wrap all the checks for that. > > > > > > > > AS_RELEASE_ALWAYS should be set if a non-NULL cookie is obtained from > > > > fscache and cleared in ->evict_inode() before truncate_inode_pages_final() > > > > is called. > > > > > > > > Additionally, the FSCACHE_COOKIE_NO_DATA_TO_READ flag needs to be cleared > > > > and the optimisation cancelled if a cachefiles object already contains data > > > > when we open it. > > > > > > > > Fixes: 1f67e6d0b188 ("fscache: Provide a function to note the release of a page") > > > > Fixes: 047487c947e8 ("cachefiles: Implement the I/O routines") > > > > Reported-by: Rohith Surabattula <rohiths.msft@xxxxxxxxx> > > > > Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx> > > > > Signed-off-by: David Howells <dhowells@xxxxxxxxxx> > > > > > > Hi David, > > > > > > I was bisecting a use-after-free BUG on the latest mm-unstable, > > > where HEAD is 347e208de0e4 ("rmap: pass the folio to __page_check_anon_rmap()"). > > > > > > According to my bisection, this is the first bad commit. > > > Use-After-Free is triggered on reclamation path when swap is enabled. > > > > This was originally occurred during kernel compilation but > > can easily be reproduced via: > > > > stress-ng --bigheap $(nproc) > > > > > (and couldn't trigger without swap enabled) > > > > > > the config, KASAN splat, bisect log are attached. > > > hope this isn't too late :( > > > > > > > cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > > > > cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > > > cc: Steve French <sfrench@xxxxxxxxx> > > > > cc: Shyam Prasad N <nspmangalore@xxxxxxxxx> > > > > cc: Rohith Surabattula <rohiths.msft@xxxxxxxxx> > > > > cc: Dave Wysochanski <dwysocha@xxxxxxxxxx> > > > > cc: Dominique Martinet <asmadeus@xxxxxxxxxxxxx> > > > > cc: Ilya Dryomov <idryomov@xxxxxxxxx> > > > > cc: linux-cachefs@xxxxxxxxxx > > > > cc: linux-cifs@xxxxxxxxxxxxxxx > > > > cc: linux-afs@xxxxxxxxxxxxxxxxxxx > > > > cc: v9fs-developer@xxxxxxxxxxxxxxxxxxxxx > > > > cc: ceph-devel@xxxxxxxxxxxxxxx > > > > cc: linux-nfs@xxxxxxxxxxxxxxx > > > > cc: linux-fsdevel@xxxxxxxxxxxxxxx > > > > cc: linux-mm@xxxxxxxxx > > > > --- > > > > > > > > Notes: > > > > ver #7) > > > > - Make NFS set AS_RELEASE_ALWAYS. > > > > > > > > ver #4) > > > > - Split out merging of folio_has_private()/filemap_release_folio() call > > > > pairs into a preceding patch. > > > > - Don't need to clear AS_RELEASE_ALWAYS in ->evict_inode(). > > > > > > > > ver #3) > > > > - Fixed mapping_clear_release_always() to use clear_bit() not set_bit(). > > > > - Moved a '&&' to the correct line. > > > > > > > > ver #2) > > > > - Rewrote entirely according to Willy's suggestion[1]. > > > > > > > > fs/9p/cache.c | 2 ++ > > > > fs/afs/internal.h | 2 ++ > > > > fs/cachefiles/namei.c | 2 ++ > > > > fs/ceph/cache.c | 2 ++ > > > > fs/nfs/fscache.c | 3 +++ > > > > fs/smb/client/fscache.c | 2 ++ > > > > include/linux/pagemap.h | 16 ++++++++++++++++ > > > > mm/internal.h | 5 ++++- > > > > 8 files changed, 33 insertions(+), 1 deletion(-) > > > I think myself / Daire Byrne may have already tracked this down and I > found a 1-liner that fixed a similar crash in his environment. > > Can you try this patch on top and let me know if it still crashes? > https://github.com/DaveWysochanskiRH/kernel/commit/902c990e311120179fa5de99d68364b2947b79ec I also encountered this issue with my DAMON tests, and was trying to find a time slot for deep dive. And I confirmed your fix works. Thank you for this great work. Please Cc me when you post the patch if possible. Tested-by: SeongJae Park <sj@xxxxxxxxxx> Thanks, SJ > > -- Linux-cachefs mailing list Linux-cachefs@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/linux-cachefs