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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rjR68-0000000GmPH-1fHY; Sun, 10 Mar 2024 21:52:48 +0000 Date: Sun, 10 Mar 2024 21:52:48 +0000 From: Matthew Wilcox To: Ryan Roberts Cc: Andrew Morton , linux-mm@kvack.org Subject: Re: [PATCH v3 10/18] mm: Allow non-hugetlb large folios to be batch processed Message-ID: References: <20240227174254.710559-1-willy@infradead.org> <20240227174254.710559-11-willy@infradead.org> <367a14f7-340e-4b29-90ae-bc3fcefdd5f4@arm.com> <8cd67a3d-81a7-4127-9d17-a1d465c3f9e8@arm.com> <02e820c2-8a1d-42cc-954b-f9e041c4417a@arm.com> <9dfd3b3b-4733-4c7c-b09c-5e6388531e49@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: D675210000B X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: qcyqhy1iy8okim4h8hfxfdorbzcdopde X-HE-Tag: 1710107572-846507 X-HE-Meta: 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 7ta55N60 6yhjNu9eEo3rfF205cH+EMZkmfZavSpRF1BEZG3OBdSmDlpNuMd5pLCfcnUoOe2gicvIQxNR2VR+sVI+I/53y+tMsPw+XqaHa05nvz1pA44zrB1FM2/IrBGF+5XJ/Yx0OZID8ca+OR6qMjJs= 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 Sun, Mar 10, 2024 at 08:46:58PM +0000, Matthew Wilcox wrote: > On Sun, Mar 10, 2024 at 07:59:46PM +0000, Ryan Roberts wrote: > > I've now been able to repro this without any of my code on top - just mm-unstable and your fix for the the memcg uncharging ordering issue. So we have separate, more difficultt to repro bug. I've discovered CONFIG_DEBUG_LIST so enabled that. I'll try to bisect in the morning, but I suspect it will be slow going. > > > > [ 390.317982] ------------[ cut here ]------------ > > [ 390.318646] list_del corruption. prev->next should be fffffc00152a9090, but was fffffc002798a490. (prev=fffffc002798a490) > > Interesting. So prev->next is pointing to prev, ie prev is an empty > list, but it should be pointing to this entry ... this is feeling like > another missing lock. Let's check that we're not inverting the order of memcg_uncharge and removing a folio from the deferred list (build tested only, but only one line of this will be new to you): diff --git a/mm/huge_memory.c b/mm/huge_memory.c index bb57b3d0c8cd..61fd1a4b424d 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -792,8 +792,6 @@ void folio_prep_large_rmappable(struct folio *folio) { if (!folio || !folio_test_large(folio)) return; - if (folio_order(folio) > 1) - INIT_LIST_HEAD(&folio->_deferred_list); folio_set_large_rmappable(folio); } diff --git a/mm/internal.h b/mm/internal.h index 79d0848c10a5..690c68c18c23 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -525,6 +525,8 @@ static inline void prep_compound_head(struct page *page, unsigned int order) atomic_set(&folio->_entire_mapcount, -1); atomic_set(&folio->_nr_pages_mapped, 0); atomic_set(&folio->_pincount, 0); + if (order > 1) + INIT_LIST_HEAD(&folio->_deferred_list); } static inline void prep_compound_tail(struct page *head, int tail_idx) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 138bcfa18234..e2334c4ee550 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -7483,6 +7483,8 @@ static void uncharge_folio(struct folio *folio, struct uncharge_gather *ug) struct obj_cgroup *objcg; VM_BUG_ON_FOLIO(folio_test_lru(folio), folio); + VM_BUG_ON_FOLIO(folio_order(folio) > 1 && + !list_empty(&folio->_deferred_list), folio); /* * Nobody should be changing or seriously looking at diff --git a/mm/page_alloc.c b/mm/page_alloc.c index bdff5c0a7c76..1c1925b92934 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1006,10 +1006,11 @@ static int free_tail_page_prepare(struct page *head_page, struct page *page) } break; case 2: - /* - * the second tail page: ->mapping is - * deferred_list.next -- ignore value. - */ + /* the second tail page: deferred_list overlaps ->mapping */ + if (unlikely(!list_empty(&folio->_deferred_list))) { + bad_page(page, "on deferred list"); + goto out; + } break; default: if (page->mapping != TAIL_MAPPING) {