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[49.181.106.210]) by smtp.gmail.com with ESMTPSA id a4-20020a1709027e4400b001801aec1f6bsm1945602pln.141.2022.10.27.21.05.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Oct 2022 21:05:57 -0700 (PDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1ooGd0-007Gjv-PK; Fri, 28 Oct 2022 15:05:54 +1100 Date: Fri, 28 Oct 2022 15:05:54 +1100 From: Dave Chinner To: Matthew Wilcox Cc: Zhaoyang Huang , "zhaoyang.huang" , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, ke.wang@unisoc.com, steve.kang@unisoc.com, baocong.liu@unisoc.com, linux-fsdevel@vger.kernel.org Subject: Re: [RFC PATCH] mm: move xa forward when run across zombie page Message-ID: <20221028040554.GU2703033@dread.disaster.area> References: <20221018223042.GJ2703033@dread.disaster.area> <20221019220424.GO2703033@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Oct 26, 2022 at 05:01:57PM +0100, Matthew Wilcox wrote: > On Thu, Oct 20, 2022 at 10:52:14PM +0100, Matthew Wilcox wrote: > > But I think the tests you've done refute that theory. I'm all out of > > ideas at the moment. > > I have a new idea. In page_cache_delete_batch(), we don't set the > order of the entry before calling xas_store(). That means we can end > up in a situation where we have an order-2 folio in the page cache, > delete it and end up with a NULL pointer at (say) index 20 and sibling > entries at indices 21-23. We can come along (potentially much later) > and put an order-0 folio back at index 20. Now all of indices 20-23 > point to the index-20, order-0 folio. Worse, the xarray node can be > freed with the sibling entries still intact and then be reallocated by > an entirely different xarray. > > I don't know if this is going to fix the problem you're seeing. I can't > quite draw a line from this situation to your symptoms. I came across > it while auditing all the places which set folio->mapping to NULL. > I did notice a mis-ordering; all the other places first remove the folio > from the xarray before setting folio to NULL, but I have a hard time > connecting that to your symptoms either. > > diff --git a/include/linux/xarray.h b/include/linux/xarray.h > index 44dd6d6e01bc..cc1fd1f849a7 100644 > --- a/include/linux/xarray.h > +++ b/include/linux/xarray.h > @@ -1617,6 +1617,12 @@ static inline void xas_advance(struct xa_state *xas, unsigned long index) > xas->xa_offset = (index >> shift) & XA_CHUNK_MASK; > } > > +static inline void xas_adjust_order(struct xa_state *xas, unsigned int order) > +{ > + xas->xa_shift = order - (order % XA_CHUNK_SHIFT); > + xas->xa_sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1; > +} > + > /** > * xas_set_order() - Set up XArray operation state for a multislot entry. > * @xas: XArray operation state. > @@ -1628,8 +1634,7 @@ static inline void xas_set_order(struct xa_state *xas, unsigned long index, > { > #ifdef CONFIG_XARRAY_MULTI > xas->xa_index = order < BITS_PER_LONG ? (index >> order) << order : 0; > - xas->xa_shift = order - (order % XA_CHUNK_SHIFT); > - xas->xa_sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1; > + xas_adjust_order(xas, order); > xas->xa_node = XAS_RESTART; > #else > BUG_ON(order > 0); > diff --git a/mm/filemap.c b/mm/filemap.c > index 08341616ae7a..6e3f486131e4 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -305,11 +305,13 @@ static void page_cache_delete_batch(struct address_space *mapping, > > WARN_ON_ONCE(!folio_test_locked(folio)); > > + if (!folio_test_hugetlb(folio)) > + xas_adjust_order(&xas, folio_order(folio)); > + xas_store(&xas, NULL); > folio->mapping = NULL; > /* Leave folio->index set: truncation lookup relies on it */ > > i++; > - xas_store(&xas, NULL); > total_pages += folio_nr_pages(folio); > } > mapping->nrpages -= total_pages; Nope, that ain't it. I think I've got the data corruption fix sorted now (at least, g/270 isn't assert failing on stray delalloc extents anymore), so if that's the case, I can spend some time actively trying to track this down.... -Dave. -- Dave Chinner david@fromorbit.com