[syzbot] [rcu?] WARNING in rcu_note_context_switch (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 51835949dda3 Merge tag 'net-next-6.11' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=150e825e980000
kernel config: https://syzkaller.appspot.com/x/.config?x=28bac69fa31fbb3a
dashboard link: https://syzkaller.appspot.com/bug?extid=784d0a1246a539975f05
compiler: aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15d4bf4e980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17a3c349980000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/384ffdcca292/non_bootable_disk-51835949.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7a3a01db5542/vmlinux-51835949.xz
kernel image: https://storage.googleapis.com/syzbot-assets/14d329019155/Image-51835949.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+784d0a...@syzkaller.appspotmail.com

------------[ cut here ]------------
Voluntary context switch within RCU read-side critical section!
WARNING: CPU: 0 PID: 3460 at kernel/rcu/tree_plugin.h:330 rcu_note_context_switch+0x354/0x49c kernel/rcu/tree_plugin.h:330
Modules linked in:
CPU: 0 PID: 3460 Comm: syz-executor248 Not tainted 6.10.0-syzkaller-04472-g51835949dda3 #0
Hardware name: linux,dummy-virt (DT)
pstate: 614000c9 (nZCv daIF +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
pc : rcu_note_context_switch+0x354/0x49c kernel/rcu/tree_plugin.h:330
lr : rcu_note_context_switch+0x354/0x49c kernel/rcu/tree_plugin.h:330
sp : ffff800089523d30
x29: ffff800089523d30 x28: f6f0000005d4a480 x27: 0000000000000000
x26: 0000000000000000 x25: f6f0000005d4a480 x24: ffff800082643318
x23: 0000000000000000 x22: f6f0000005d4a480 x21: fff000007f8d6240
x20: ffff80008261e040 x19: fff000007f8d7040 x18: fffffffffffcb658
x17: fff07ffffd2b9000 x16: ffff800080000000 x15: 0000000000000048
x14: fffffffffffcb6a0 x13: ffff80008266b0a8 x12: 000000000000088b
x11: 00000000000002d9 x10: ffff80008271f500 x9 : ffff80008266b0a8
x8 : 00000000ffffdfff x7 : ffff80008271b0a8 x6 : 00000000000002d9
x5 : fff000007f8cbf48 x4 : 40000000ffffe2d9 x3 : fff07ffffd2b9000
x2 : 0000000000000000 x1 : 0000000000000000 x0 : f6f0000005d4a480
Call trace:
rcu_note_context_switch+0x354/0x49c kernel/rcu/tree_plugin.h:330
__schedule+0xb0/0x850 kernel/sched/core.c:6417
__schedule_loop kernel/sched/core.c:6606 [inline]
schedule+0x34/0x104 kernel/sched/core.c:6621
do_notify_resume+0xe4/0x164 arch/arm64/kernel/entry-common.c:136
exit_to_user_mode_prepare arch/arm64/kernel/entry-common.c:169 [inline]
exit_to_user_mode arch/arm64/kernel/entry-common.c:178 [inline]
el0_interrupt+0xc4/0xc8 arch/arm64/kernel/entry-common.c:797
__el0_irq_handler_common+0x18/0x24 arch/arm64/kernel/entry-common.c:802
el0t_64_irq_handler+0x10/0x1c arch/arm64/kernel/entry-common.c:807
el0t_64_irq+0x19c/0x1a0 arch/arm64/kernel/entry.S:599
---[ end trace 0000000000000000 ]---


---
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If the report is already addressed, let syzbot know by replying with:
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#syz undup

[Paul E. McKenney]

On Sun, Jul 21, 2024 at 05:53:21AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 51835949dda3 Merge tag 'net-next-6.11' of git://git.kernel..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=150e825e980000
> kernel config: https://syzkaller.appspot.com/x/.config?x=28bac69fa31fbb3a
> dashboard link: https://syzkaller.appspot.com/bug?extid=784d0a1246a539975f05
> compiler: aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> userspace arch: arm64
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15d4bf4e980000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17a3c349980000
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/384ffdcca292/non_bootable_disk-51835949.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/7a3a01db5542/vmlinux-51835949.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/14d329019155/Image-51835949.gz.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+784d0a...@syzkaller.appspotmail.com
>
> ------------[ cut here ]------------
> Voluntary context switch within RCU read-side critical section!
> WARNING: CPU: 0 PID: 3460 at kernel/rcu/tree_plugin.h:330 rcu_note_context_switch+0x354/0x49c kernel/rcu/tree_plugin.h:330

Taking a voluntary context switch in an RCU read-side critical section
voids your RCU warranty.

If we are exiting to user mode, my first guess would be that someone
did rcu_read_lock() but forgot the matching rcu_read_unlock().

Can this be reproduced using lockdep? That would pinpoint the unmatched
rcu_read_lock().

Thanx, Paul

[Z qiang]

This should be caused by this modification (commit id:
ca567df74a28a9fb368c6b2d93e864113f73f5c2)
when tsk is null, miss invoke rcu_read_unlock() for NS_GET_TGID_IN_PIDNS.

Thanks
Zqiang

[Paul E. McKenney]

Very good, and it looks like that to me as well. Would you like to
submit a fix patch and see if syzbot agrees?

Thanx, Paul

[Z qiang]

I see there is a c test
program(https://syzkaller.appspot.com/x/repro.c?x=17a3c349980000),
I will run this test on my local machine, and then make a fix.

Thanks
Zqiang

[Boqun Feng]

On Mon, Jul 22, 2024 at 02:42:10PM +0800, Z qiang wrote:
[...]

> > >
> > > This should be caused by this modification (commit id:
> > > ca567df74a28a9fb368c6b2d93e864113f73f5c2)
> > > when tsk is null, miss invoke rcu_read_unlock() for NS_GET_TGID_IN_PIDNS.
> >
> > Very good, and it looks like that to me as well. Would you like to
> > submit a fix patch and see if syzbot agrees?
>
> I see there is a c test
> program(https://syzkaller.appspot.com/x/repro.c?x=17a3c349980000),
> I will run this test on my local machine, and then make a fix.
>

FWIW, syzbot provides a way to do tests automatically:

https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches

But looks like Christian already fixed this:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=280e36f0d5b997173d014c07484c03a7f7750668

Regards,
Boqun

> Thanks
> Zqiang
>
>
[...]

[Edward Adam Davis]

miss rcu read unlock

#syz test: upstream 51835949dda3

diff --git a/fs/nsfs.c b/fs/nsfs.c
index a4a925dce331..e228d06f0949 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -188,8 +188,10 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
tsk = find_task_by_vpid(arg);
else
tsk = find_task_by_pid_ns(arg, pid_ns);
- if (!tsk)
+ if (!tsk) {
+ rcu_read_unlock();
break;
+ }

switch (ioctl) {
case NS_GET_PID_FROM_PIDNS:

[syzbot]

Hello,

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

Reported-by: syzbot+784d0a...@syzkaller.appspotmail.com
Tested-by: syzbot+784d0a...@syzkaller.appspotmail.com

Tested on:

commit: 51835949 Merge tag 'net-next-6.11' of git://git.kernel..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=15eedb79980000

kernel config: https://syzkaller.appspot.com/x/.config?x=28bac69fa31fbb3a
dashboard link: https://syzkaller.appspot.com/bug?extid=784d0a1246a539975f05
compiler: aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64

patch: https://syzkaller.appspot.com/x/patch.diff?x=120e5ead980000

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

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.