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Date: Tue, 21 Dec 2021 10:24:27 -0800
From: Yang Shi <shy828301@...il.com>
To: syzbot <syzbot+1f52b3a18d5633fa7f82@...kaller.appspotmail.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Alistair Popple <apopple@...dia.com>,
chinwen.chang@...iatek.com, fgheet255t@...il.com,
Jann Horn <jannh@...gle.com>,
Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
"Kirill A. Shutemov" <kirill@...temov.name>,
Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux MM <linux-mm@...ck.org>, Peter Xu <peterx@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
syzkaller-bugs@...glegroups.com, tonymarislogistics@...dex.com,
Vlastimil Babka <vbabka@...e.cz>, walken@...gle.com,
Matthew Wilcox <willy@...radead.org>, Zi Yan <ziy@...dia.com>
Subject: Re: [syzbot] kernel BUG in __page_mapcount
On Tue, Dec 21, 2021 at 9:24 AM syzbot
<syzbot+1f52b3a18d5633fa7f82@...kaller.appspotmail.com> wrote:
>
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 6e0567b73052 Merge tag 'for-linus' of git://git.kernel.org..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14c192b3b00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=ae22d1ee4fbca18
> dashboard link: https://syzkaller.appspot.com/bug?extid=1f52b3a18d5633fa7f82
> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=133200fdb00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17c3102db00000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+1f52b3a18d5633fa7f82@...kaller.appspotmail.com
>
> __mmput+0x122/0x4b0 kernel/fork.c:1113
> mmput+0x56/0x60 kernel/fork.c:1134
> exit_mm kernel/exit.c:507 [inline]
> do_exit+0xb27/0x2b40 kernel/exit.c:819
> do_group_exit+0x125/0x310 kernel/exit.c:929
> get_signal+0x47d/0x2220 kernel/signal.c:2852
> arch_do_signal_or_restart+0x2a9/0x1c40 arch/x86/kernel/signal.c:868
> handle_signal_work kernel/entry/common.c:148 [inline]
> exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
> exit_to_user_mode_prepare+0x17d/0x290 kernel/entry/common.c:207
> __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
> syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:300
> do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> ------------[ cut here ]------------
> kernel BUG at include/linux/page-flags.h:785!
> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 4392 Comm: syz-executor560 Not tainted 5.16.0-rc6-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:PageDoubleMap include/linux/page-flags.h:785 [inline]
> RIP: 0010:__page_mapcount+0x2d2/0x350 mm/util.c:744
It seems the THP is split during smaps walk. The reproducer does call
MADV_FREE on partial THP which may split the huge page.
The below fix (untested) should be able to fix it.
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index ad667dbc96f5..97feb15a2448 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -433,6 +433,7 @@ static void smaps_account(struct mem_size_stats
*mss, struct page *page,
{
int i, nr = compound ? compound_nr(page) : 1;
unsigned long size = nr * PAGE_SIZE;
+ struct page *head = compound_head(page);
/*
* First accumulate quantities that depend only on |size| and the type
@@ -462,6 +463,11 @@ static void smaps_account(struct mem_size_stats
*mss, struct page *page,
locked, true);
return;
}
+
+ /* Lost the race with THP split */
+ if (!get_page_unless_zero(head))
+ return;
+
for (i = 0; i < nr; i++, page++) {
int mapcount = page_mapcount(page);
unsigned long pss = PAGE_SIZE << PSS_SHIFT;
@@ -470,6 +476,8 @@ static void smaps_account(struct mem_size_stats
*mss, struct page *page,
smaps_page_accumulate(mss, page, PAGE_SIZE, pss, dirty, locked,
mapcount < 2);
}
+
+ put_page(head);
}
> Code: e8 d3 16 d1 ff 48 c7 c6 c0 00 b6 89 48 89 ef e8 94 4e 04 00 0f 0b e8 bd 16 d1 ff 48 c7 c6 60 01 b6 89 48 89 ef e8 7e 4e 04 00 <0f> 0b e8 a7 16 d1 ff 48 c7 c6 a0 01 b6 89 4c 89 f7 e8 68 4e 04 00
> RSP: 0018:ffffc90002b6f7b8 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffff888019619d00 RSI: ffffffff81a68c12 RDI: 0000000000000003
> RBP: ffffea0001bdc2c0 R08: 0000000000000029 R09: 00000000ffffffff
> R10: ffffffff8903e29f R11: 00000000ffffffff R12: 00000000ffffffff
> R13: 00000000ffffea00 R14: ffffc90002b6fb30 R15: ffffea0001bd8001
> FS: 00007faa2aefd700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fff7e663318 CR3: 0000000018c6e000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> page_mapcount include/linux/mm.h:837 [inline]
> smaps_account+0x470/0xb10 fs/proc/task_mmu.c:466
> smaps_pte_entry fs/proc/task_mmu.c:538 [inline]
> smaps_pte_range+0x611/0x1250 fs/proc/task_mmu.c:601
> walk_pmd_range mm/pagewalk.c:128 [inline]
> walk_pud_range mm/pagewalk.c:205 [inline]
> walk_p4d_range mm/pagewalk.c:240 [inline]
> walk_pgd_range mm/pagewalk.c:277 [inline]
> __walk_page_range+0xe23/0x1ea0 mm/pagewalk.c:379
> walk_page_vma+0x277/0x350 mm/pagewalk.c:530
> smap_gather_stats.part.0+0x148/0x260 fs/proc/task_mmu.c:768
> smap_gather_stats fs/proc/task_mmu.c:741 [inline]
> show_smap+0xc6/0x440 fs/proc/task_mmu.c:822
> seq_read_iter+0xbb0/0x1240 fs/seq_file.c:272
> seq_read+0x3e0/0x5b0 fs/seq_file.c:162
> vfs_read+0x1b5/0x600 fs/read_write.c:479
> ksys_read+0x12d/0x250 fs/read_write.c:619
> 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+0x44/0xae
> RIP: 0033:0x7faa2af6c969
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 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:00007faa2aefd288 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> RAX: ffffffffffffffda RBX: 00007faa2aff4418 RCX: 00007faa2af6c969
> RDX: 0000000000002025 RSI: 0000000020000100 RDI: 0000000000000003
> RBP: 00007faa2aff4410 R08: 00007faa2aefd700 R09: 0000000000000000
> R10: 00007faa2aefd700 R11: 0000000000000246 R12: 00007faa2afc20ac
> R13: 00007fff7e6632bf R14: 00007faa2aefd400 R15: 0000000000022000
> </TASK>
> Modules linked in:
> ---[ end trace 24ec93ff95e4ac3d ]---
> RIP: 0010:PageDoubleMap include/linux/page-flags.h:785 [inline]
> RIP: 0010:__page_mapcount+0x2d2/0x350 mm/util.c:744
> Code: e8 d3 16 d1 ff 48 c7 c6 c0 00 b6 89 48 89 ef e8 94 4e 04 00 0f 0b e8 bd 16 d1 ff 48 c7 c6 60 01 b6 89 48 89 ef e8 7e 4e 04 00 <0f> 0b e8 a7 16 d1 ff 48 c7 c6 a0 01 b6 89 4c 89 f7 e8 68 4e 04 00
> RSP: 0018:ffffc90002b6f7b8 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffff888019619d00 RSI: ffffffff81a68c12 RDI: 0000000000000003
> RBP: ffffea0001bdc2c0 R08: 0000000000000029 R09: 00000000ffffffff
> R10: ffffffff8903e29f R11: 00000000ffffffff R12: 00000000ffffffff
> R13: 00000000ffffea00 R14: ffffc90002b6fb30 R15: ffffea0001bd8001
> FS: 00007faa2aefd700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fff7e663318 CR3: 0000000018c6e000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>
>
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