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Mon, 21 Oct 2024 17:01:59 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id j4m8IweJFmdeCQAAD6G6ig (envelope-from ); Mon, 21 Oct 2024 17:01:59 +0000 Message-ID: Date: Mon, 21 Oct 2024 19:01:59 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: page_alloc: move mlocked flag clearance into free_pages_prepare() Content-Language: en-US To: Roman Gushchin , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Hugh Dickins , Matthew Wilcox References: <20241021164837.2681358-1-roman.gushchin@linux.dev> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <20241021164837.2681358-1-roman.gushchin@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Score: -4.30 X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.991]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[7]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:mid,syzkaller.appspot.com:url] X-Spam-Flag: NO X-Spam-Level: On 10/21/24 18:48, Roman Gushchin wrote: > Syzbot reported [1] a bad page state problem caused by a page > being freed using free_page() still having a mlocked flag at > free_pages_prepare() stage: > > BUG: Bad page state in process syz.0.15 pfn:1137bb > page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff8881137bb870 pfn:0x1137bb > flags: 0x400000000080000(mlocked|node=0|zone=1) > raw: 0400000000080000 0000000000000000 dead000000000122 0000000000000000 > raw: ffff8881137bb870 0000000000000000 00000000ffffffff 0000000000000000 > page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set > page_owner tracks the page as allocated > page last allocated via order 0, migratetype Unmovable, gfp_mask > 0x400dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO), pid 3005, tgid > 3004 (syz.0.15), ts 61546 608067, free_ts 61390082085 > set_page_owner include/linux/page_owner.h:32 [inline] > post_alloc_hook+0x1f3/0x230 mm/page_alloc.c:1537 > prep_new_page mm/page_alloc.c:1545 [inline] > get_page_from_freelist+0x3008/0x31f0 mm/page_alloc.c:3457 > __alloc_pages_noprof+0x292/0x7b0 mm/page_alloc.c:4733 > alloc_pages_mpol_noprof+0x3e8/0x630 mm/mempolicy.c:2265 > kvm_coalesced_mmio_init+0x1f/0xf0 virt/kvm/coalesced_mmio.c:99 > kvm_create_vm virt/kvm/kvm_main.c:1235 [inline] > kvm_dev_ioctl_create_vm virt/kvm/kvm_main.c:5500 [inline] > kvm_dev_ioctl+0x13bb/0x2320 virt/kvm/kvm_main.c:5542 > vfs_ioctl fs/ioctl.c:51 [inline] > __do_sys_ioctl fs/ioctl.c:907 [inline] > __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0x69/0x110 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > page last free pid 951 tgid 951 stack trace: > reset_page_owner include/linux/page_owner.h:25 [inline] > free_pages_prepare mm/page_alloc.c:1108 [inline] > free_unref_page+0xcb1/0xf00 mm/page_alloc.c:2638 > vfree+0x181/0x2e0 mm/vmalloc.c:3361 > delayed_vfree_work+0x56/0x80 mm/vmalloc.c:3282 > process_one_work kernel/workqueue.c:3229 [inline] > process_scheduled_works+0xa5c/0x17a0 kernel/workqueue.c:3310 > worker_thread+0xa2b/0xf70 kernel/workqueue.c:3391 > kthread+0x2df/0x370 kernel/kthread.c:389 > ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 > > The problem was originally introduced by > commit b109b87050df ("mm/munlock: replace clear_page_mlock() by final > clearance"): it was handling focused on handling pagecache > and anonymous memory and wasn't suitable for lower level > get_page()/free_page() API's used for example by KVM, as with > this reproducer. Does that mean KVM is mlocking pages that are not pagecache nor anonymous, thus not LRU? How and why (and since when) is that done? > Fix it by moving the mlocked flag clearance down to > free_page_prepare(). > > The bug itself if fairly old and harmless (aside from generating these > warnings), so the stable backport is likely not justified. But since there's a Cc: stable below, it will be backported :) > Closes: https://syzkaller.appspot.com/x/report.txt?x=169a47d0580000 > Fixes: b109b87050df ("mm/munlock: replace clear_page_mlock() by final clearance") > Signed-off-by: Roman Gushchin > Cc: > Cc: Hugh Dickins > Cc: Matthew Wilcox > --- > mm/page_alloc.c | 9 +++++++++ > mm/swap.c | 14 -------------- > 2 files changed, 9 insertions(+), 14 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index bc55d39eb372..24200651ad92 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1044,6 +1044,7 @@ __always_inline bool free_pages_prepare(struct page *page, > bool skip_kasan_poison = should_skip_kasan_poison(page); > bool init = want_init_on_free(); > bool compound = PageCompound(page); > + struct folio *folio = page_folio(page); > > VM_BUG_ON_PAGE(PageTail(page), page); > > @@ -1053,6 +1054,14 @@ __always_inline bool free_pages_prepare(struct page *page, > if (memcg_kmem_online() && PageMemcgKmem(page)) > __memcg_kmem_uncharge_page(page, order); > > + if (unlikely(folio_test_mlocked(folio))) { > + long nr_pages = folio_nr_pages(folio); > + > + __folio_clear_mlocked(folio); > + zone_stat_mod_folio(folio, NR_MLOCK, -nr_pages); > + count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages); > + } Why drop the useful comment? > + > if (unlikely(PageHWPoison(page)) && !order) { > /* Do not let hwpoison pages hit pcplists/buddy */ > reset_page_owner(page, order); > diff --git a/mm/swap.c b/mm/swap.c > index 835bdf324b76..7cd0f4719423 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -78,20 +78,6 @@ static void __page_cache_release(struct folio *folio, struct lruvec **lruvecp, > lruvec_del_folio(*lruvecp, folio); > __folio_clear_lru_flags(folio); > } > - > - /* > - * In rare cases, when truncation or holepunching raced with > - * munlock after VM_LOCKED was cleared, Mlocked may still be > - * found set here. This does not indicate a problem, unless > - * "unevictable_pgs_cleared" appears worryingly large. > - */ > - if (unlikely(folio_test_mlocked(folio))) { > - long nr_pages = folio_nr_pages(folio); > - > - __folio_clear_mlocked(folio); > - zone_stat_mod_folio(folio, NR_MLOCK, -nr_pages); > - count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages); > - } > } > > /*