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Message-ID: <Y2rU6BHD9eePn8IN@dhcp22.suse.cz>
Date: Tue, 8 Nov 2022 23:15:04 +0100
From: Michal Hocko <mhocko@...e.com>
To: Yang Shi <shy828301@...il.com>
Cc: zokeefe@...gle.com, akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
syzbot+0044b22d177870ee974f@...kaller.appspotmail.com
Subject: Re: [mm-unstable v3 PATCH 3/3] mm: replace VM_WARN_ON to pr_warn if
the node is offline with __GFP_THISNODE
On Tue 08-11-22 10:43:57, 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:
> <TASK>
> 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
> </TASK>
>
> 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@...kaller.appspotmail.com
> Signed-off-by: Yang Shi <shy828301@...il.com>
> Suggested-by: Michal Hocko <mhocko@...e.com>
> Cc: Zach O'Keefe <zokeefe@...gle.com>
Acked-by: Michal Hocko <mhocko@...e.com>
minor nit
> ---
> 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);
I would use rather this_node or similarly descriptive name. gfp sounds
like a pasm but this is only a subset of it. If you really want to
improve the readability then you can restructure the condition a bit
if (gfp_mask & (__GFP_THISNODE|__GFP_NOWARN)) != (__GFP_THISNODE|__GFP_NOWARN))
return;
if (node_online(nid))
return;
pr_warn("%pGg allocation from offline node %d\n", &gfp, nid);
dump_stack();
> +
> + if ((gfp == (__GFP_THISNODE|__GFP_NOWARN)) && !node_online(nid)) {
> + pr_warn("%pGg allocation from offline node %d\n", &gfp, nid);
> + dump_stack();
> + }
> +}
> +
--
Michal Hocko
SUSE Labs
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