Re: [syzbot] WARNING in do_mkdirat

[Hillf Danton <hdanton@sina.com>]

On Sat, 03 Dec 2022 06:52:45 -0800
> syzbot found the following issue on:
> 
> HEAD commit:    ca57f02295f1 afs: Fix fileserver probe RTT handling
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=171b06a1880000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2325e409a9a893e1
> dashboard link: https://syzkaller.appspot.com/bug?extid=919c5a9be8433b8bf201
> compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/af66f1d3a389/disk-ca57f022.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/c0c7ec393108/vmlinux-ca57f022.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/ea8871940eaa/bzImage-ca57f022.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+919c5a9be8433b8bf201@syzkaller.appspotmail.com
> 
> WARNING: CPU: 0 PID: 12206 at kernel/locking/rwsem.c:1361 __up_write kernel/locking/rwsem.c:1360 [inline]
> WARNING: CPU: 0 PID: 12206 at kernel/locking/rwsem.c:1361 up_write+0x4f9/0x580 kernel/locking/rwsem.c:1615
> Modules linked in:
> CPU: 0 PID: 12206 Comm: syz-executor.0 Not tainted 6.1.0-rc7-syzkaller-00012-gca57f02295f1 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> RIP: 0010:__up_write kernel/locking/rwsem.c:1360 [inline]
> RIP: 0010:up_write+0x4f9/0x580 kernel/locking/rwsem.c:1615
> Code: c7 40 a3 ed 8a 48 c7 c6 e0 a5 ed 8a 48 8b 54 24 28 48 8b 4c 24 18 4d 89 e0 4c 8b 4c 24 30 31 c0 53 e8 1b 83 e8 ff 48 83 c4 08 <0f> 0b e9 6b fd ff ff 48 c7 c1 18 25 76 8e 80 e1 07 80 c1 03 38 c1
> RSP: 0018:ffffc9000338fd40 EFLAGS: 00010292
> RAX: 69eb1955c47aff00 RBX: ffffffff8aeda420 RCX: 0000000000040000
> RDX: ffffc900046f6000 RSI: 0000000000023311 RDI: 0000000000023312
> RBP: ffffc9000338fe10 R08: ffffffff816e560d R09: fffff52000671f61
> R10: fffff52000671f61 R11: 1ffff92000671f60 R12: 0000000000000000
> R13: ffff888027d20a90 R14: 1ffff92000671fb0 R15: dffffc0000000000
> FS:  00007f928b35b700(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f268cbad988 CR3: 000000001e90f000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  inode_unlock include/linux/fs.h:761 [inline]
>  done_path_create fs/namei.c:3857 [inline]
>  do_mkdirat+0x2de/0x550 fs/namei.c:4064
>  __do_sys_mkdir fs/namei.c:4081 [inline]
>  __se_sys_mkdir fs/namei.c:4079 [inline]
>  __x64_sys_mkdir+0x6a/0x80 fs/namei.c:4079
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f928a68c0d9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 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:00007f928b35b168 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
> RAX: ffffffffffffffda RBX: 00007f928a7ac050 RCX: 00007f928a68c0d9
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000400
> RBP: 00007f928a6e7ae9 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fffeaab152f R14: 00007f928b35b300 R15: 0000000000022000
>  </TASK>

Add debug info to inode_unlock() to see if this is not a bogus report.

Hillf

--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -758,6 +758,7 @@ static inline void inode_lock(struct ino
 
 static inline void inode_unlock(struct inode *inode)
 {
+	lockdep_assert_held_write(&inode->i_rwsem);
 	up_write(&inode->i_rwsem);
 }
 
--