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dkim=pass header.d=google.com header.s=20210112 header.b=tI7lDymu; spf=pass (imf16.hostedemail.com: domain of zokeefe@google.com designates 209.85.208.182 as permitted sender) smtp.mailfrom=zokeefe@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam07 X-Stat-Signature: zafrp6ss5bf11sgkcsbf3cwwk4q8opuw X-Rspamd-Queue-Id: DEB4C180007 X-HE-Tag: 1667261144-447163 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: On Mon, Oct 31, 2022 at 3:08 PM Michal Hocko wrote: > > On Mon 31-10-22 11:31:22, Yang Shi wrote: > > 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 > > This is quite weird, isn't it? alloc_charge_hpage is selecting the most > busy node (as per collapse_control). How come this can be an offline > node? Is a parallel memory hotplug happening? TBH -- I did not look closely at the syzbot reproducer (let alone attempt to run it) and assumed this was the case. Taking a quick look, at least memory hot remove is enabled: CONFIG_ARCH_ENABLE_MEMORY_HOTPLUG=y CONFIG_ARCH_ENABLE_MEMORY_HOTREMOVE=y CONFIG_MEMORY_HOTPLUG=y CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE=y CONFIG_MEMORY_HOTREMOVE=y But looking at the C reproducer, I don't immediately see anywhere where we offline nodes. I'll try to run this tomorrow to make sure I'm not missing something real here. Thanks, Zach > [...] > > > It is because khugepaged allocates pages with __GFP_THISNODE, but the > > preferred node is offlined. The warning was even stronger before commit > > 8addc2d00fe17 ("mm: do not warn on offline nodes unless the specific node > > is explicitly requested"). The commit softened the warning for > > __GFP_THISNODE. > > > > But this warning seems not quite useful because: > > * There is no guarantee the node is online for __GFP_THISNODE context > > for all the callsites. > > The original idea IIRC was to catch a buggy code which mishandled node > assignment. But this looks like a perfectly valid code. There is no > synchronization with the memory hotplug so it is possible that memory > gets offline during a longer taking scanning. > > I do agree that the warning is not really helpful in this case. It is > actually even harmful for those running in panic-on-warn mode. > > > * Kernel just fails the allocation regardless the warning, and it looks > > all callsites handle the allocation failure gracefully. > > > > So, removing the warning seems like the good move. > > > > Reported-by: syzbot+0044b22d177870ee974f@syzkaller.appspotmail.com > > Signed-off-by: Yang Shi > > Cc: Zach O'Keefe > > Cc: Michal Hocko > > Unless I am wrong in my above statement I would appreciate extending the > changelog to describe the actual code is correct so the warning is > harmful. > > Acked-by: Michal Hocko > > > --- > > include/linux/gfp.h | 2 -- > > 1 file changed, 2 deletions(-) > > > > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > > index ef4aea3b356e..594d6dee5646 100644 > > --- a/include/linux/gfp.h > > +++ b/include/linux/gfp.h > > @@ -218,7 +218,6 @@ 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)); > > > > return __alloc_pages(gfp_mask, order, nid, NULL); > > } > > @@ -227,7 +226,6 @@ 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)); > > > > return __folio_alloc(gfp, order, nid, NULL); > > } > > -- > > 2.26.3 > > -- > Michal Hocko > SUSE Labs