kernel BUG at lib/lockref.c:LINE!

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: d58b5ab9 Add linux-next specific files for 20190708
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=123d6887a00000
kernel config: https://syzkaller.appspot.com/x/.config?x=bf9882946ecc11d9
dashboard link: https://syzkaller.appspot.com/bug?extid=f70e9b00f8c7d4187bd0
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=173375c7a00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1536f9bfa00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f70e9b...@syzkaller.appspotmail.com

------------[ cut here ]------------
kernel BUG at lib/lockref.c:189!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 9350 Comm: syz-executor444 Not tainted 5.2.0-next-20190708 #33
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:lockref_mark_dead lib/lockref.c:189 [inline]
RIP: 0010:lockref_mark_dead+0x8b/0xa0 lib/lockref.c:187
Code: 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 0f b6 04 02 84 c0 74 04 3c 03
7e 1d c7 43 38 80 ff ff ff 5b 41 5c 5d c3 e8 75 19 38 fe <0f> 0b 48 89 df
e8 0b 59 72 fe eb ab e8 a4 59 72 fe eb dc 90 90 55
RSP: 0018:ffff88809004fc90 EFLAGS: 00010293
RAX: ffff88808bcc0300 RBX: ffff8880a69b0520 RCX: ffffffff833a3abf
RDX: 0000000000000000 RSI: ffffffff833a3afb RDI: 0000000000000005
RBP: ffff88809004fca0 R08: ffff88808bcc0300 R09: ffffed1014d360a5
R10: ffffed1014d360a4 R11: ffff8880a69b0523 R12: 0000000000000000
R13: ffff8880a69b0520 R14: ffff8880a69b04a0 R15: 0000000000000000
FS: 000055555571f880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555555738938 CR3: 0000000091be1000 CR4: 00000000001406f0
Call Trace:
__dentry_kill+0x5f/0x600 fs/dcache.c:560
shrink_dcache_parent+0x2c9/0x3d0 fs/dcache.c:1565
vfs_rmdir fs/namei.c:3882 [inline]
vfs_rmdir+0x26f/0x4f0 fs/namei.c:3857
do_rmdir+0x39e/0x420 fs/namei.c:3940
__do_sys_rmdir fs/namei.c:3958 [inline]
__se_sys_rmdir fs/namei.c:3956 [inline]
__x64_sys_rmdir+0x36/0x40 fs/namei.c:3956
do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x441917
Code: 0f 1f 00 b8 57 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 ad 09 fc ff c3
66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 54 00 00 00 0f 05 <48> 3d 01 f0 ff
ff 0f 83 8d 09 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe53fc08f8 EFLAGS: 00000207 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 0000000000000065 RCX: 0000000000441917
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffe53fc1a90
RBP: 00000000000024ef R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000005 R11: 0000000000000207 R12: 00007ffe53fc1a90
R13: 00005555557288c0 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 407254279c8c4b61 ]---
RIP: 0010:lockref_mark_dead lib/lockref.c:189 [inline]
RIP: 0010:lockref_mark_dead+0x8b/0xa0 lib/lockref.c:187
Code: 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 0f b6 04 02 84 c0 74 04 3c 03
7e 1d c7 43 38 80 ff ff ff 5b 41 5c 5d c3 e8 75 19 38 fe <0f> 0b 48 89 df
e8 0b 59 72 fe eb ab e8 a4 59 72 fe eb dc 90 90 55
RSP: 0018:ffff88809004fc90 EFLAGS: 00010293
RAX: ffff88808bcc0300 RBX: ffff8880a69b0520 RCX: ffffffff833a3abf
RDX: 0000000000000000 RSI: ffffffff833a3afb RDI: 0000000000000005
RBP: ffff88809004fca0 R08: ffff88808bcc0300 R09: ffffed1014d360a5
R10: ffffed1014d360a4 R11: ffff8880a69b0523 R12: 0000000000000000
R13: ffff8880a69b0520 R14: ffff8880a69b04a0 R15: 0000000000000000
FS: 000055555571f880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555555738938 CR3: 0000000091be1000 CR4: 00000000001406f0


---
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[Al Viro]

On Mon, Jul 08, 2019 at 12:37:06PM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: d58b5ab9 Add linux-next specific files for 20190708
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=123d6887a00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=bf9882946ecc11d9
> dashboard link: https://syzkaller.appspot.com/bug?extid=f70e9b00f8c7d4187bd0
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=173375c7a00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1536f9bfa00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+f70e9b...@syzkaller.appspotmail.com
>
> ------------[ cut here ]------------
> kernel BUG at lib/lockref.c:189!

Mea culpa... It's "Teach shrink_dcache_parent() to cope with mixed-filesystem
shrink lists", and the fix should be simply this:

diff --git a/fs/dcache.c b/fs/dcache.c
index d8732cf2e302..d85d8f2c8c97 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1555,6 +1555,7 @@ void shrink_dcache_parent(struct dentry *parent)
d_walk(parent, &data, select_collect2);
if (data.victim) {
struct dentry *parent;
+ spin_lock(&data.victim->d_lock);
if (!shrink_lock_dentry(data.victim)) {
rcu_read_unlock();
} else {

[syzbot]

syzbot has bisected this bug to:

commit 867c90eeea9d81ad1336881b61a4dcf692fc5d50
Author: Stephen Rothwell <s...@canb.auug.org.au>
Date: Mon Jul 8 00:22:38 2019 +0000

Merge remote-tracking branch 'xfs/for-next'

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16c69bc3a00000
start commit: d58b5ab9 Add linux-next specific files for 20190708
git tree: linux-next
final crash: https://syzkaller.appspot.com/x/report.txt?x=15c69bc3a00000
console output: https://syzkaller.appspot.com/x/log.txt?x=11c69bc3a00000

kernel config: https://syzkaller.appspot.com/x/.config?x=bf9882946ecc11d9
dashboard link: https://syzkaller.appspot.com/bug?extid=f70e9b00f8c7d4187bd0

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=173375c7a00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1536f9bfa00000

Reported-by: syzbot+f70e9b...@syzkaller.appspotmail.com
Fixes: 867c90eeea9d ("Merge remote-tracking branch 'xfs/for-next'")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Eric Biggers]

This bug is incorrectly marked as fixed by 'fix the braino in "Teach
shrink_dcache_parent() to cope with mixed-filesystem shrink lists"', which
doesn't exist, so syzbot can't close this bug. But the fix was actually folded
into the patch which introduced this bug, "Teach shrink_dcache_parent() to cope
with mixed-filesystem shrink lists". Telling syzbot:

#syz invalid