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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rRvPz-0000000092M-35Es; Mon, 22 Jan 2024 14:36:55 +0000 Date: Mon, 22 Jan 2024 14:36:55 +0000 From: Matthew Wilcox To: Miaohe Lin Cc: naoya.horiguchi@nec.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/memory-failure: fix crash in split_huge_page_to_list from soft_offline_page Message-ID: References: <20240120065729.3276395-1-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 40D7216001A X-Stat-Signature: cba7gpnp9nk1i1y9qzdz5xsf3uto3fej X-HE-Tag: 1705934217-742578 X-HE-Meta: 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 Yt2ob6KV TZvxzIYIP0N5MuVImvaTNVn3laYPiFIXuJbm2UzTCPirkdDCJiqHODPup7FZBt80FD6TCU+18sSPpmp1ffc+6ZhAUWAe9QxU5VyM78Z+HJ2bjsayCpPFgf71tlSOvB0dOZUb82zkjPpOFha2f+tWQv3nNx03QzMBCJ1d3LkMkXgJen6wMldcEqXVVKQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jan 22, 2024 at 08:57:06PM +0800, Miaohe Lin wrote: > On 2024/1/21 10:00, Matthew Wilcox wrote: > > On Sat, Jan 20, 2024 at 02:57:29PM +0800, Miaohe Lin wrote: > >> { > >> - /* Soft offline could migrate non-LRU movable pages */ > >> - if ((flags & MF_SOFT_OFFLINE) && __PageMovable(page)) > >> + /* > >> + * Soft offline could migrate non-LRU movable pages. > >> + * Note that page->mapping is overloaded with slab->slab_list or slabs > >> + * fields which might make slab pages appear like non-LRU movable pages. > >> + * So __PageMovable() has to be done after PageSlab() is checked. > >> + */ > >> + if ((flags & MF_SOFT_OFFLINE) && !PageSlab(page) && __PageMovable(page)) > >> return true; > >> > >> return PageLRU(page) || is_free_buddy_page(page); > > > > I think would make more sense as > > > > + if (PageSlab(page)) > > + return false; > > Do you mean add PageSlab check above "if ((flags & MF_SOFT_OFFLINE) && __PageMovable(page))" block > so we don't need to add more comment? Yes, although not just that we don't need to add a comment. Fundamentally, if you see PageSlab, you don't need to test anything else, you know it's not migratable. > I have a concern that __PageMovable() seems unreliable now if we access page from random context. > This might introduce some potential problems. For example, offline_pages() might be stumped with > such pages without any progress until signal occurs IIUC: > > offline_pages > .. > do { > scan_movable_pages > if (__PageMovable(page)) -- It might be slab page here. ret will also be set to 0. > goto found; > do_migrate_range -- Failed to isolate slab page and retry. > } while (!ret) -- retry since ret is 0. > > There might be many similar scenes, but I haven't taken them more closely. Maybe these are > just dumb problems... Yep, lots of places are insufficiently careful about testing PageMovable. This will get fixed with memdescs, but we're a fair way from having memdescs ...