[syzbot] INFO: rcu detected stall in sys_setxattr (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b2d229d4ddb1 Linux 5.18-rc3
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=144417ccf00000
kernel config: https://syzkaller.appspot.com/x/.config?x=6cb89c879305f336
dashboard link: https://syzkaller.appspot.com/bug?extid=10a16d1c43580983f6a2
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=104a88e8f00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=132a840cf00000

The issue was bisected to:

commit e257039f0fc7da36ac3a522ef9a5cb4ae7852e67
Author: Al Viro <vi...@zeniv.linux.org.uk>
Date: Tue Mar 1 04:04:20 2022 +0000

mount_setattr(): clean the control flow and calling conventions

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16b313c0f00000
final oops: https://syzkaller.appspot.com/x/report.txt?x=15b313c0f00000
console output: https://syzkaller.appspot.com/x/log.txt?x=11b313c0f00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+10a16d...@syzkaller.appspotmail.com
Fixes: e257039f0fc7 ("mount_setattr(): clean the control flow and calling conventions")

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 1-....: (10500 ticks this GP) idle=bb3/1/0x4000000000000000 softirq=5340/5340 fqs=5250
(t=10502 jiffies g=4461 q=33)
NMI backtrace for cpu 1
CPU: 1 PID: 3616 Comm: syz-executor364 Not tainted 5.18.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106
nmi_cpu_backtrace+0x473/0x4a0 lib/nmi_backtrace.c:111
nmi_trigger_cpumask_backtrace+0x168/0x280 lib/nmi_backtrace.c:62
trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
rcu_dump_cpu_stacks+0x236/0x3a0 kernel/rcu/tree_stall.h:343
print_cpu_stall kernel/rcu/tree_stall.h:639 [inline]
check_cpu_stall kernel/rcu/tree_stall.h:723 [inline]
rcu_pending kernel/rcu/tree.c:3923 [inline]
rcu_sched_clock_irq+0xf1b/0x18d0 kernel/rcu/tree.c:2625
update_process_times+0x197/0x200 kernel/time/timer.c:1788
tick_sched_handle kernel/time/tick-sched.c:243 [inline]
tick_sched_timer+0x377/0x540 kernel/time/tick-sched.c:1473
__run_hrtimer kernel/time/hrtimer.c:1685 [inline]
__hrtimer_run_queues+0x4cb/0xa60 kernel/time/hrtimer.c:1749
hrtimer_interrupt+0x3a6/0xfd0 kernel/time/hrtimer.c:1811
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1086 [inline]
__sysvec_apic_timer_interrupt+0xf9/0x280 arch/x86/kernel/apic/apic.c:1103
sysvec_apic_timer_interrupt+0x8c/0xb0 arch/x86/kernel/apic/apic.c:1097
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x12/0x20
RIP: 0010:__mnt_want_write+0xd7/0x2a0 fs/namespace.c:348
Code: bd 00 02 00 00 be 00 02 00 00 44 21 fe 31 ff e8 1f f4 98 ff 44 21 fd 75 0a e8 f5 ef 98 ff eb 3a 0f 1f 00 f3 90 42 0f b6 04 2b <84> c0 75 10 41 f7 06 00 02 00 00 74 1e e8 d7 ef 98 ff eb e5 44 89
RSP: 0018:ffffc90003acfda8 EFLAGS: 00000293
RAX: 0000000000000000 RBX: 1ffff11002261706 RCX: ffff8880197f0000
RDX: 0000000000000000 RSI: 0000000000000200 RDI: 0000000000000000
RBP: 0000000000000200 R08: ffffffff81eccb11 R09: fffffbfff1bc082e
R10: fffffbfff1bc082e R11: 1ffffffff1bc082d R12: ffff88801130b820
R13: dffffc0000000000 R14: ffff88801130b830 R15: 0000000000000220
mnt_want_write+0x43/0x80 fs/namespace.c:394
path_setxattr+0x117/0x2b0 fs/xattr.c:593
__do_sys_setxattr fs/xattr.c:611 [inline]
__se_sys_setxattr fs/xattr.c:607 [inline]
__x64_sys_setxattr+0xb7/0xd0 fs/xattr.c:607
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f418ef7cce9
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:00007f418ef0d2f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000bc
RAX: ffffffffffffffda RBX: 00007f418f0044b0 RCX: 00007f418ef7cce9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000200
RBP: 00007f418efd2084 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0030656c69662f2e
R13: 695f70756f72672c R14: 695f726573752c30 R15: 00007f418f0044b8
</TASK>
----------------
Code disassembly (best guess):
0: bd 00 02 00 00 mov $0x200,%ebp
5: be 00 02 00 00 mov $0x200,%esi
a: 44 21 fe and %r15d,%esi
d: 31 ff xor %edi,%edi
f: e8 1f f4 98 ff callq 0xff98f433
14: 44 21 fd and %r15d,%ebp
17: 75 0a jne 0x23
19: e8 f5 ef 98 ff callq 0xff98f013
1e: eb 3a jmp 0x5a
20: 0f 1f 00 nopl (%rax)
23: f3 90 pause
25: 42 0f b6 04 2b movzbl (%rbx,%r13,1),%eax
* 2a: 84 c0 test %al,%al <-- trapping instruction
2c: 75 10 jne 0x3e
2e: 41 f7 06 00 02 00 00 testl $0x200,(%r14)
35: 74 1e je 0x55
37: e8 d7 ef 98 ff callq 0xff98f013
3c: eb e5 jmp 0x23
3e: 44 rex.R
3f: 89 .byte 0x89


---
This report is generated by a bot. It may contain errors.
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Hillf Danton]

On Tue, 19 Apr 2022 09:16:20 -0700

Get one more MNT_WRITE_HOLD cleared in the error branch.

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/ b2d229d4ddb1

--- y/fs/namespace.c
+++ x/fs/namespace.c
@@ -4034,6 +4034,7 @@ static int mount_setattr_prepare(struct
{
struct mount *m;
int err;
+ int undo_m = 0;

for (m = mnt; m; m = next_mnt(m, mnt)) {
if (!can_change_locked_flags(m, recalc_flags(kattr, m))) {
@@ -4047,8 +4048,10 @@ static int mount_setattr_prepare(struct

if (!mnt_allow_writers(kattr, m)) {
err = mnt_hold_writers(m);
- if (err)
+ if (err) {
+ undo_m = 1;
break;
+ }
}

if (!kattr->recurse)
@@ -4063,6 +4066,9 @@ static int mount_setattr_prepare(struct
if (p->mnt.mnt_flags & MNT_WRITE_HOLD)
mnt_unhold_writers(p);
}
+ if (undo_m)
+ if (m->mnt.mnt_flags & MNT_WRITE_HOLD)
+ mnt_unhold_writers(m);
}
return err;
}
--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+10a16d...@syzkaller.appspotmail.com

Tested on:

commit: b2d229d4 Linux 5.18-rc3
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
kernel config: https://syzkaller.appspot.com/x/.config?x=34d641b059469a42
dashboard link: https://syzkaller.appspot.com/bug?extid=10a16d1c43580983f6a2
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch: https://syzkaller.appspot.com/x/patch.diff?x=14302ff0f00000

Note: testing is done by a robot and is best-effort only.

[Christian Brauner]

On Tue, Apr 19, 2022 at 09:16:20AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: b2d229d4ddb1 Linux 5.18-rc3
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=144417ccf00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=6cb89c879305f336
> dashboard link: https://syzkaller.appspot.com/bug?extid=10a16d1c43580983f6a2
> compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=104a88e8f00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=132a840cf00000
>
> The issue was bisected to:
>
> commit e257039f0fc7da36ac3a522ef9a5cb4ae7852e67
> Author: Al Viro <vi...@zeniv.linux.org.uk>
> Date: Tue Mar 1 04:04:20 2022 +0000
>
> mount_setattr(): clean the control flow and calling conventions
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16b313c0f00000
> final oops: https://syzkaller.appspot.com/x/report.txt?x=15b313c0f00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=11b313c0f00000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+10a16d...@syzkaller.appspotmail.com
> Fixes: e257039f0fc7 ("mount_setattr(): clean the control flow and calling conventions")

This suspiciously looks like in the case of failing to make a single
read-write mount read-only we don't unset MNT_WRITE_HOLD in the new
error path that Al added.

Just saw that Hilf was testing a patch to this effect as well so putting
him on this thread.

Hilf, are you working on a fix for this I can pick up from you later or
should I come up with a patch?

Christian

[Christian Brauner]

On Tue, Apr 19, 2022 at 09:16:20AM -0700, syzbot wrote:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: b2d229d4ddb1 Linux 5.18-rc3
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=144417ccf00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=6cb89c879305f336
> dashboard link: https://syzkaller.appspot.com/bug?extid=10a16d1c43580983f6a2
> compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=104a88e8f00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=132a840cf00000
>
> The issue was bisected to:
>
> commit e257039f0fc7da36ac3a522ef9a5cb4ae7852e67
> Author: Al Viro <vi...@zeniv.linux.org.uk>
> Date: Tue Mar 1 04:04:20 2022 +0000
>
> mount_setattr(): clean the control flow and calling conventions
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16b313c0f00000
> final oops: https://syzkaller.appspot.com/x/report.txt?x=15b313c0f00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=11b313c0f00000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+10a16d...@syzkaller.appspotmail.com
> Fixes: e257039f0fc7 ("mount_setattr(): clean the control flow and calling conventions")

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git fs.mount_setattr.cleanup

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+10a16d...@syzkaller.appspotmail.com

Tested on:

commit: bbc1e8c5 fs: unset MNT_WRITE_HOLD on failure
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git fs.mount_setattr.cleanup
kernel config: https://syzkaller.appspot.com/x/.config?x=34d641b059469a42
dashboard link: https://syzkaller.appspot.com/bug?extid=10a16d1c43580983f6a2
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Note: no patches were applied.