Re: [syzbot] kernel BUG in __page_mapcount
From: Yang Shi <hidden>
Date: 2021-12-21 18:24:44
Also in:
linux-fsdevel, lkml
Subsystem:
filesystems (vfs and infrastructure), memory mapping, proc filesystem, the rest · Maintainers:
Alexander Viro, Christian Brauner, Andrew Morton, Liam R. Howlett, Lorenzo Stoakes, Linus Torvalds
On Tue, Dec 21, 2021 at 9:24 AM syzbot [off-list ref] 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@syzkaller.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