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[67.174.241.145]) by smtp.gmail.com with ESMTPSA id ij22-20020a170902ab5600b0017f36638010sm7210438plb.276.2022.11.08.10.44.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Nov 2022 10:44:24 -0800 (PST) From: Yang Shi To: zokeefe@google.com, mhocko@suse.com, akpm@linux-foundation.org Cc: shy828301@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+0044b22d177870ee974f@syzkaller.appspotmail.com Subject: [mm-unstable v3 PATCH 3/3] mm: replace VM_WARN_ON to pr_warn if the node is offline with __GFP_THISNODE Date: Tue, 8 Nov 2022 10:43:57 -0800 Message-Id: <20221108184357.55614-3-shy828301@gmail.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221108184357.55614-1-shy828301@gmail.com> References: <20221108184357.55614-1-shy828301@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Syzbot reported the below splat: WARNING: CPU: 1 PID: 3646 at include/linux/gfp.h:221 __alloc_pages_node include/linux/gfp.h:221 [inline] WARNING: CPU: 1 PID: 3646 at include/linux/gfp.h:221 hpage_collapse_alloc_page mm/khugepaged.c:807 [inline] WARNING: CPU: 1 PID: 3646 at include/linux/gfp.h:221 alloc_charge_hpage+0x802/0xaa0 mm/khugepaged.c:963 Modules linked in: CPU: 1 PID: 3646 Comm: syz-executor210 Not tainted 6.1.0-rc1-syzkaller-00454-ga70385240892 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022 RIP: 0010:__alloc_pages_node include/linux/gfp.h:221 [inline] RIP: 0010:hpage_collapse_alloc_page mm/khugepaged.c:807 [inline] RIP: 0010:alloc_charge_hpage+0x802/0xaa0 mm/khugepaged.c:963 Code: e5 01 4c 89 ee e8 6e f9 ae ff 4d 85 ed 0f 84 28 fc ff ff e8 70 fc ae ff 48 8d 6b ff 4c 8d 63 07 e9 16 fc ff ff e8 5e fc ae ff <0f> 0b e9 96 fa ff ff 41 bc 1a 00 00 00 e9 86 fd ff ff e8 47 fc ae RSP: 0018:ffffc90003fdf7d8 EFLAGS: 00010293 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffff888077f457c0 RSI: ffffffff81cd8f42 RDI: 0000000000000001 RBP: ffff888079388c0c R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000000 FS: 00007f6b48ccf700(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f6b48a819f0 CR3: 00000000171e7000 CR4: 00000000003506e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: collapse_file+0x1ca/0x5780 mm/khugepaged.c:1715 hpage_collapse_scan_file+0xd6c/0x17a0 mm/khugepaged.c:2156 madvise_collapse+0x53a/0xb40 mm/khugepaged.c:2611 madvise_vma_behavior+0xd0a/0x1cc0 mm/madvise.c:1066 madvise_walk_vmas+0x1c7/0x2b0 mm/madvise.c:1240 do_madvise.part.0+0x24a/0x340 mm/madvise.c:1419 do_madvise mm/madvise.c:1432 [inline] __do_sys_madvise mm/madvise.c:1432 [inline] __se_sys_madvise mm/madvise.c:1430 [inline] __x64_sys_madvise+0x113/0x150 mm/madvise.c:1430 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f6b48a4eef9 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f6b48ccf318 EFLAGS: 00000246 ORIG_RAX: 000000000000001c RAX: ffffffffffffffda RBX: 00007f6b48af0048 RCX: 00007f6b48a4eef9 RDX: 0000000000000019 RSI: 0000000000600003 RDI: 0000000020000000 RBP: 00007f6b48af0040 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6b48aa53a4 R13: 00007f6b48bffcbf R14: 00007f6b48ccf400 R15: 0000000000022000 It is because khugepaged allocates pages with __GFP_THISNODE, but the preferred node is bogus. The previous patch fixed the khugepaged code to avoid allocating page from non-existing node. But it is still racy against memory hotremove. There is no synchronization with the memory hotplug so it is possible that memory gets offline during a longer taking scanning. So this warning still seems not quite helpful because: * There is no guarantee the node is online for __GFP_THISNODE context for all the callsites. * Kernel just fails the allocation regardless the warning, and it looks all callsites handle the allocation failure gracefully. Although while the warning has helped to identify a buggy code, it is not safe in general and this warning could panic the system with panic-on-warn configuration which tends to be used surprisingly often. So replace VM_WARN_ON to pr_warn(). And the warning will be triggered if __GFP_NOWARN is set since the allocator would print out warning for such case if __GFP_NOWARN is not set. Reported-by: syzbot+0044b22d177870ee974f@syzkaller.appspotmail.com Signed-off-by: Yang Shi Suggested-by: Michal Hocko Cc: Zach O'Keefe --- v3: * Reverted the old commit from mm-unstable which remove the VM_WARN (patch 1/3). * Incorporated the suggestion from Michal to use pr_warn. v2: * Added patch 1/2. * Reworded the commit log per Michal. include/linux/gfp.h | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/include/linux/gfp.h b/include/linux/gfp.h index ef4aea3b356e..60a1c70ec85c 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h @@ -210,6 +210,16 @@ alloc_pages_bulk_array_node(gfp_t gfp, int nid, unsigned long nr_pages, struct p return __alloc_pages_bulk(gfp, nid, NULL, nr_pages, NULL, page_array); } +static inline void warn_if_node_offline(int nid, gfp_t gfp_mask) +{ + gfp_t gfp = gfp_mask & (__GFP_THISNODE|__GFP_NOWARN); + + if ((gfp == (__GFP_THISNODE|__GFP_NOWARN)) && !node_online(nid)) { + pr_warn("%pGg allocation from offline node %d\n", &gfp, nid); + dump_stack(); + } +} + /* * Allocate pages, preferring the node given as nid. The node must be valid and * online. For more general interface, see alloc_pages_node(). @@ -218,7 +228,7 @@ static inline struct page * __alloc_pages_node(int nid, gfp_t gfp_mask, unsigned int order) { VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES); - VM_WARN_ON((gfp_mask & __GFP_THISNODE) && !node_online(nid)); + warn_if_node_offline(nid, gfp_mask); return __alloc_pages(gfp_mask, order, nid, NULL); } @@ -227,7 +237,7 @@ static inline struct folio *__folio_alloc_node(gfp_t gfp, unsigned int order, int nid) { VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES); - VM_WARN_ON((gfp & __GFP_THISNODE) && !node_online(nid)); + warn_if_node_offline(nid, gfp); return __folio_alloc(gfp, order, nid, NULL); } -- 2.35.1