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[syzbot] [kernel?] inconsistent lock state in ptrace_attach

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f31817cbcf48 Add linux-next specific files for 20231116
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=112158fb680000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f59345f1d0a928c
dashboard link: https://syzkaller.appspot.com/bug?extid=cbb25bb9b4d29a773985
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/987488cb251e/disk-f31817cb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6d4a82d8bd4b/vmlinux-f31817cb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fc43dee9cb86/bzImage-f31817cb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cbb25bb9b4d29a773985@syzkaller.appspotmail.com

================================
WARNING: inconsistent lock state
6.7.0-rc1-next-20231116-syzkaller #0 Not tainted
--------------------------------
inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage.
syz-executor.1/5657 [HC0[0]:SC0[0]:HE1:SE1] takes:
ffff88807ba4a518 (&sighand->siglock){?.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff88807ba4a518 (&sighand->siglock){?.-.}-{2:2}, at: class_spinlock_constructor include/linux/spinlock.h:530 [inline]
ffff88807ba4a518 (&sighand->siglock){?.-.}-{2:2}, at: ptrace_set_stopped kernel/ptrace.c:391 [inline]
ffff88807ba4a518 (&sighand->siglock){?.-.}-{2:2}, at: ptrace_attach+0x401/0x650 kernel/ptrace.c:478
{IN-HARDIRQ-W} state was registered at:
  lock_acquire kernel/locking/lockdep.c:5753 [inline]
  lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
  _raw_spin_lock_irqsave+0x3a/0x50 kernel/locking/spinlock.c:162
  __lock_task_sighand+0xc2/0x340 kernel/signal.c:1422
  lock_task_sighand include/linux/sched/signal.h:748 [inline]
  send_sigqueue+0x1d4/0x840 kernel/signal.c:1996
  posix_timer_event kernel/time/posix-timers.c:298 [inline]
  posix_timer_fn+0x181/0x3d0 kernel/time/posix-timers.c:324
  __run_hrtimer kernel/time/hrtimer.c:1688 [inline]
  __hrtimer_run_queues+0x20c/0xc20 kernel/time/hrtimer.c:1752
  hrtimer_interrupt+0x31b/0x800 kernel/time/hrtimer.c:1814
  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1065 [inline]
  __sysvec_apic_timer_interrupt+0x10c/0x410 arch/x86/kernel/apic/apic.c:1082
  sysvec_apic_timer_interrupt+0x90/0xb0 arch/x86/kernel/apic/apic.c:1076
  asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
  lock_acquire+0x1f2/0x530 kernel/locking/lockdep.c:5721
  rcu_lock_acquire include/linux/rcupdate.h:301 [inline]
  rcu_read_lock include/linux/rcupdate.h:747 [inline]
  batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:408 [inline]
  batadv_nc_worker+0x16e/0x10e0 net/batman-adv/network-coding.c:719
  process_one_work+0x8a4/0x15f0 kernel/workqueue.c:2636
  process_scheduled_works kernel/workqueue.c:2709 [inline]
  worker_thread+0x8b6/0x1290 kernel/workqueue.c:2790
  kthread+0x2c1/0x3a0 kernel/kthread.c:388
  ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
irq event stamp: 1111
hardirqs last  enabled at (1111): [<ffffffff8a84a34e>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:151 [inline]
hardirqs last  enabled at (1111): [<ffffffff8a84a34e>] _raw_spin_unlock_irqrestore+0x4e/0x70 kernel/locking/spinlock.c:194
hardirqs last disabled at (1110): [<ffffffff8a84a0fe>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (1110): [<ffffffff8a84a0fe>] _raw_spin_lock_irqsave+0x4e/0x50 kernel/locking/spinlock.c:162
softirqs last  enabled at (1016): [<ffffffff81310072>] local_bh_enable include/linux/bottom_half.h:33 [inline]
softirqs last  enabled at (1016): [<ffffffff81310072>] fpregs_unlock arch/x86/include/asm/fpu/api.h:80 [inline]
softirqs last  enabled at (1016): [<ffffffff81310072>] fpu_clone+0x342/0xb60 arch/x86/kernel/fpu/core.c:634
softirqs last disabled at (1014): [<ffffffff81310007>] local_bh_disable include/linux/bottom_half.h:20 [inline]
softirqs last disabled at (1014): [<ffffffff81310007>] fpregs_lock arch/x86/include/asm/fpu/api.h:72 [inline]
softirqs last disabled at (1014): [<ffffffff81310007>] fpu_clone+0x2d7/0xb60 arch/x86/kernel/fpu/core.c:630

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&sighand->siglock);
  <Interrupt>
    lock(&sighand->siglock);

 *** DEADLOCK ***

2 locks held by syz-executor.1/5657:
 #0: ffff888022a1e3c8 (&sig->cred_guard_mutex){+.+.}-{3:3}, at: class_mutex_intr_constructor include/linux/mutex.h:225 [inline]
 #0: ffff888022a1e3c8 (&sig->cred_guard_mutex){+.+.}-{3:3}, at: ptrace_attach+0x1eb/0x650 kernel/ptrace.c:455
 #1: ffffffff8cc0a098 (tasklist_lock){++++}-{2:2}, at: class_write_lock_constructor include/linux/spinlock.h:564 [inline]
 #1: ffffffff8cc0a098 (tasklist_lock){++++}-{2:2}, at: ptrace_attach+0x2c3/0x650 kernel/ptrace.c:464

stack backtrace:
CPU: 0 PID: 5657 Comm: syz-executor.1 Not tainted 6.7.0-rc1-next-20231116-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
 print_usage_bug kernel/locking/lockdep.c:3970 [inline]
 valid_state kernel/locking/lockdep.c:4012 [inline]
 mark_lock_irq kernel/locking/lockdep.c:4215 [inline]
 mark_lock+0x91a/0xc50 kernel/locking/lockdep.c:4677
 mark_usage kernel/locking/lockdep.c:4586 [inline]
 __lock_acquire+0x919/0x3b10 kernel/locking/lockdep.c:5090
 lock_acquire kernel/locking/lockdep.c:5753 [inline]
 lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:351 [inline]
 class_spinlock_constructor include/linux/spinlock.h:530 [inline]
 ptrace_set_stopped kernel/ptrace.c:391 [inline]
 ptrace_attach+0x401/0x650 kernel/ptrace.c:478
 __do_sys_ptrace+0x204/0x230 kernel/ptrace.c:1290
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x62/0x6a
RIP: 0033:0x7f390ac7cae9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f390ba5a0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000065
RAX: ffffffffffffffda RBX: 00007f390ad9c1f0 RCX: 00007f390ac7cae9
RDX: 0000000000000000 RSI: 000000000000005c RDI: 0000000000000010
RBP: 00007f390acc847a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000006e R14: 00007f390ad9c1f0 R15: 00007ffe8ba90308
 </TASK>


---
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Re: [syzbot] [kernel?] inconsistent lock state in ptrace_attach

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    f31817cbcf48 Add linux-next specific files for 20231116
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=168778a8e80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f59345f1d0a928c
dashboard link: https://syzkaller.appspot.com/bug?extid=cbb25bb9b4d29a773985
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12e34b97680000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15c8aca7680000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/987488cb251e/disk-f31817cb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6d4a82d8bd4b/vmlinux-f31817cb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fc43dee9cb86/bzImage-f31817cb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cbb25bb9b4d29a773985@syzkaller.appspotmail.com

================================
WARNING: inconsistent lock state
6.7.0-rc1-next-20231116-syzkaller #0 Not tainted
--------------------------------
inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage.
syz-executor207/5059 [HC0[0]:SC0[0]:HE1:SE1] takes:
ffff888025c41298 (&sighand->siglock){?...}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff888025c41298 (&sighand->siglock){?...}-{2:2}, at: class_spinlock_constructor include/linux/spinlock.h:530 [inline]
ffff888025c41298 (&sighand->siglock){?...}-{2:2}, at: ptrace_set_stopped kernel/ptrace.c:391 [inline]
ffff888025c41298 (&sighand->siglock){?...}-{2:2}, at: ptrace_attach+0x401/0x650 kernel/ptrace.c:478
{IN-HARDIRQ-W} state was registered at:
  lock_acquire kernel/locking/lockdep.c:5753 [inline]
  lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
  _raw_spin_lock_irqsave+0x3a/0x50 kernel/locking/spinlock.c:162
  __lock_task_sighand+0xc2/0x340 kernel/signal.c:1422
  lock_task_sighand include/linux/sched/signal.h:748 [inline]
  send_sigqueue+0x1d4/0x840 kernel/signal.c:1996
  posix_timer_event kernel/time/posix-timers.c:298 [inline]
  posix_timer_fn+0x181/0x3d0 kernel/time/posix-timers.c:324
  __run_hrtimer kernel/time/hrtimer.c:1688 [inline]
  __hrtimer_run_queues+0x20c/0xc20 kernel/time/hrtimer.c:1752
  hrtimer_interrupt+0x31b/0x800 kernel/time/hrtimer.c:1814
  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1065 [inline]
  __sysvec_apic_timer_interrupt+0x10c/0x410 arch/x86/kernel/apic/apic.c:1082
  sysvec_apic_timer_interrupt+0x90/0xb0 arch/x86/kernel/apic/apic.c:1076
  asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
  __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:151 [inline]
  _raw_spin_unlock_irqrestore+0x31/0x70 kernel/locking/spinlock.c:194
  spin_unlock_irqrestore include/linux/spinlock.h:406 [inline]
  unlock_timer kernel/time/posix-timers.c:128 [inline]
  do_timer_settime+0x260/0x2f0 kernel/time/posix-timers.c:934
  __do_sys_timer_settime kernel/time/posix-timers.c:954 [inline]
  __se_sys_timer_settime kernel/time/posix-timers.c:940 [inline]
  __x64_sys_timer_settime+0x266/0x2c0 kernel/time/posix-timers.c:940
  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
  do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
  entry_SYSCALL_64_after_hwframe+0x62/0x6a
irq event stamp: 13807
hardirqs last  enabled at (13807): [<ffffffff8a84a34e>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:151 [inline]
hardirqs last  enabled at (13807): [<ffffffff8a84a34e>] _raw_spin_unlock_irqrestore+0x4e/0x70 kernel/locking/spinlock.c:194
hardirqs last disabled at (13806): [<ffffffff8a84a0fe>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (13806): [<ffffffff8a84a0fe>] _raw_spin_lock_irqsave+0x4e/0x50 kernel/locking/spinlock.c:162
softirqs last  enabled at (13794): [<ffffffff813146a1>] local_bh_enable include/linux/bottom_half.h:33 [inline]
softirqs last  enabled at (13794): [<ffffffff813146a1>] fpregs_unlock arch/x86/include/asm/fpu/api.h:80 [inline]
softirqs last  enabled at (13794): [<ffffffff813146a1>] restore_fpregs_from_user arch/x86/kernel/fpu/signal.c:330 [inline]
softirqs last  enabled at (13794): [<ffffffff813146a1>] __fpu_restore_sig+0x6a1/0x13a0 arch/x86/kernel/fpu/signal.c:361
softirqs last disabled at (13792): [<ffffffff81314365>] local_bh_disable include/linux/bottom_half.h:20 [inline]
softirqs last disabled at (13792): [<ffffffff81314365>] fpregs_lock arch/x86/include/asm/fpu/api.h:72 [inline]
softirqs last disabled at (13792): [<ffffffff81314365>] restore_fpregs_from_user arch/x86/kernel/fpu/signal.c:284 [inline]
softirqs last disabled at (13792): [<ffffffff81314365>] __fpu_restore_sig+0x365/0x13a0 arch/x86/kernel/fpu/signal.c:361

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&sighand->siglock);
  <Interrupt>
    lock(&sighand->siglock);

 *** DEADLOCK ***

2 locks held by syz-executor207/5059:
 #0: ffff88801d66e3c8 (&sig->cred_guard_mutex){+.+.}-{3:3}, at: class_mutex_intr_constructor include/linux/mutex.h:225 [inline]
 #0: ffff88801d66e3c8 (&sig->cred_guard_mutex){+.+.}-{3:3}, at: ptrace_attach+0x1eb/0x650 kernel/ptrace.c:455
 #1: ffffffff8cc0a098 (tasklist_lock){++++}-{2:2}, at: class_write_lock_constructor include/linux/spinlock.h:564 [inline]
 #1: ffffffff8cc0a098 (tasklist_lock){++++}-{2:2}, at: ptrace_attach+0x2c3/0x650 kernel/ptrace.c:464

stack backtrace:
CPU: 0 PID: 5059 Comm: syz-executor207 Not tainted 6.7.0-rc1-next-20231116-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
 print_usage_bug kernel/locking/lockdep.c:3970 [inline]
 valid_state kernel/locking/lockdep.c:4012 [inline]
 mark_lock_irq kernel/locking/lockdep.c:4215 [inline]
 mark_lock+0x91a/0xc50 kernel/locking/lockdep.c:4677
 mark_usage kernel/locking/lockdep.c:4586 [inline]
 __lock_acquire+0x919/0x3b10 kernel/locking/lockdep.c:5090
 lock_acquire kernel/locking/lockdep.c:5753 [inline]
 lock_acquire+0x1b1/0x530 kernel/locking/lockdep.c:5718
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:351 [inline]
 class_spinlock_constructor include/linux/spinlock.h:530 [inline]
 ptrace_set_stopped kernel/ptrace.c:391 [inline]
 ptrace_attach+0x401/0x650 kernel/ptrace.c:478
 __do_sys_ptrace+0x204/0x230 kernel/ptrace.c:1290
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x62/0x6a
RIP: 0033:0x7f726faf87f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f726fab7158 EFLAGS: 00000246 ORIG_RAX: 0000000000000065
RAX: ffffffffffffffda RBX: 00007f726fb7f328 RCX: 00007f726faf87f9
RDX: 0000000000000000 RSI: 00000000000013c4 RDI: 0000000000000010
RBP: 00007f726fb7f320 R08: 00007f726fab76c0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f726fb7f32c
R13: 0000000000000000 R14: 00007ffd413eb1b0 R15: 00007ffd413eb298
 </TASK>


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

Re: [syzbot] [kernel?] inconsistent lock state in ptrace_attach

[syzbot]

syzbot has bisected this issue to:

commit 2d25a889601d2fbc87ec79b30ea315820f874b78
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Sun Sep 17 11:24:21 2023 +0000

    ptrace: Convert ptrace_attach() to use lock guards

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=132b7d84e80000
start commit:   f31817cbcf48 Add linux-next specific files for 20231116
git tree:       linux-next
final oops:     https://syzkaller.appspot.com/x/report.txt?x=10ab7d84e80000
console output: https://syzkaller.appspot.com/x/log.txt?x=172b7d84e80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f59345f1d0a928c
dashboard link: https://syzkaller.appspot.com/bug?extid=cbb25bb9b4d29a773985
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1014d797680000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11b1ec67680000

Reported-by: syzbot+cbb25bb9b4d29a773985@syzkaller.appspotmail.com
Fixes: 2d25a889601d ("ptrace: Convert ptrace_attach() to use lock guards")

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

Re: [syzbot] [kernel?] inconsistent lock state in ptrace_attach

[Peter Zijlstra]

On Fri, Nov 17, 2023 at 12:49:04AM -0800, syzbot wrote:
> syzbot has bisected this issue to:
> 
> commit 2d25a889601d2fbc87ec79b30ea315820f874b78
> Author: Peter Zijlstra <peterz@infradead.org>
> Date:   Sun Sep 17 11:24:21 2023 +0000
> 
>     ptrace: Convert ptrace_attach() to use lock guards
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=132b7d84e80000
> start commit:   f31817cbcf48 Add linux-next specific files for 20231116
> git tree:       linux-next
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=10ab7d84e80000
> console output: https://syzkaller.appspot.com/x/log.txt?x=172b7d84e80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f59345f1d0a928c
> dashboard link: https://syzkaller.appspot.com/bug?extid=cbb25bb9b4d29a773985
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1014d797680000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11b1ec67680000
> 
> Reported-by: syzbot+cbb25bb9b4d29a773985@syzkaller.appspotmail.com
> Fixes: 2d25a889601d ("ptrace: Convert ptrace_attach() to use lock guards")

Hurmph, let me pull that patch from tip and go have a look. Thanks!

Re: [syzbot] [kernel?] inconsistent lock state in ptrace_attach

[Oleg Nesterov]

On 11/17, Peter Zijlstra wrote:
>
> On Fri, Nov 17, 2023 at 12:49:04AM -0800, syzbot wrote:
> > syzbot has bisected this issue to:
> >
> > commit 2d25a889601d2fbc87ec79b30ea315820f874b78
> > Author: Peter Zijlstra <peterz@infradead.org>
> > Date:   Sun Sep 17 11:24:21 2023 +0000
> >
> >     ptrace: Convert ptrace_attach() to use lock guards
> >
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=132b7d84e80000
> > start commit:   f31817cbcf48 Add linux-next specific files for 20231116
> > git tree:       linux-next
> > final oops:     https://syzkaller.appspot.com/x/report.txt?x=10ab7d84e80000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=172b7d84e80000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=f59345f1d0a928c
> > dashboard link: https://syzkaller.appspot.com/bug?extid=cbb25bb9b4d29a773985
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1014d797680000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11b1ec67680000
> >
> > Reported-by: syzbot+cbb25bb9b4d29a773985@syzkaller.appspotmail.com
> > Fixes: 2d25a889601d ("ptrace: Convert ptrace_attach() to use lock guards")
>
> Hurmph, let me pull that patch from tip and go have a look. Thanks!

I guess

	scoped_guard (write_lock, &tasklist_lock)

is not right... this needs write_lock_irq().

I didn't notice this when I reviewed this patch.

Oleg.

Re: [syzbot] [kernel?] inconsistent lock state in ptrace_attach

[Peter Zijlstra]

On Fri, Nov 17, 2023 at 10:38:30AM +0100, Oleg Nesterov wrote:
> On 11/17, Peter Zijlstra wrote:
> >
> > On Fri, Nov 17, 2023 at 12:49:04AM -0800, syzbot wrote:
> > > syzbot has bisected this issue to:
> > >
> > > commit 2d25a889601d2fbc87ec79b30ea315820f874b78
> > > Author: Peter Zijlstra <peterz@infradead.org>
> > > Date:   Sun Sep 17 11:24:21 2023 +0000
> > >
> > >     ptrace: Convert ptrace_attach() to use lock guards
> > >
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=132b7d84e80000
> > > start commit:   f31817cbcf48 Add linux-next specific files for 20231116
> > > git tree:       linux-next
> > > final oops:     https://syzkaller.appspot.com/x/report.txt?x=10ab7d84e80000
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=172b7d84e80000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=f59345f1d0a928c
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=cbb25bb9b4d29a773985
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1014d797680000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11b1ec67680000
> > >
> > > Reported-by: syzbot+cbb25bb9b4d29a773985@syzkaller.appspotmail.com
> > > Fixes: 2d25a889601d ("ptrace: Convert ptrace_attach() to use lock guards")
> >
> > Hurmph, let me pull that patch from tip and go have a look. Thanks!
> 
> I guess
> 
> 	scoped_guard (write_lock, &tasklist_lock)
> 
> is not right... this needs write_lock_irq().
> 
> I didn't notice this when I reviewed this patch.

Yep, that seems to be the case.

I keep forgetting how to tell the syscall robot to test the below delta,
but I'll push the ammended commit to my staging tree and we'll see what
happens.

---
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -461,7 +461,7 @@ static int ptrace_attach(struct task_str
 				return retval;
 		}
 
-		scoped_guard (write_lock, &tasklist_lock) {
+		scoped_guard (write_lock_irq, &tasklist_lock) {
 			if (unlikely(task->exit_state))
 				return -EPERM;
 			if (task->ptrace)

Re: [syzbot] Test

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Subject: Test
Author: tintinm2017@gmail.com

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

Re: [syzbot] Test

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Subject: Test
Author: tintinm2017@gmail.com

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

Re: [syzbot] [kernel?] inconsistent lock state in ptrace_attach

[Oleg Nesterov]

On 11/17, Peter Zijlstra wrote:
>
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -461,7 +461,7 @@ static int ptrace_attach(struct task_str
>  				return retval;
>  		}
>
> -		scoped_guard (write_lock, &tasklist_lock) {
> +		scoped_guard (write_lock_irq, &tasklist_lock) {

FWIW,

Acked-by: Oleg Nesterov <oleg@redhat.com>

Re: [syzbot] Test

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Subject: Test
Author: tintinm2017@gmail.com

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

Re: [syzbot] Test

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Subject: Test
Author: tintinm2017@gmail.com

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

Re: [syzbot] Test

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Subject: Test
Author: tintinm2017@gmail.com

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

Re: [syzbot] Test

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Subject: Test
Author: tintinm2017@gmail.com

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

Re: [syzbot] Test

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Subject: Test
Author: tintinm2017@gmail.com

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

Re: [syzbot] test

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Subject: test
Author: tintinm2017@gmail.com

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

[syzbot] Test

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Subject: Test
Author: tintinm2017@gmail.com

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

Re: [syzbot] Test

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Subject: Test
Author: tintinm2017@gmail.com

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

Re: [syzbot] Test

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Subject: Test
Author: mukattreyee@gmail.com

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

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

Re: [syzbot] test

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Author: mukattreyee@gmail.com

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

Re: [syzbot] Test

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Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 71b1543c83d65af8215d7558d70fc2ecbee77dcf

---
 net/sched/sch_taprio.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index a0d54b422186..41add4a1d407 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -44,6 +44,8 @@ static struct static_key_false taprio_have_working_mqprio;
 	(TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST | TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)
 #define TAPRIO_FLAGS_INVALID U32_MAX
 
+#define TAPRIO_MAX_NUM_SCHEDULES_BEFORE_NOW 10
+
 struct sched_entry {
 	/* Durations between this GCL entry and the GCL entry where the
 	 * respective traffic class gate closes
@@ -62,6 +64,8 @@ struct sched_entry {
 	u32 gate_mask;
 	u32 interval;
 	u8 command;
+	/* Used to skip some cycles to prevent other tasks from starving */
+	u8 num_schedules_before_now;
 };
 
 struct sched_gate_list {
@@ -111,6 +115,9 @@ struct __tc_taprio_qopt_offload {
 	struct tc_taprio_qopt_offload offload;
 };
 
+static void setup_txtime(struct taprio_sched *q,
+			 struct sched_gate_list *sched, ktime_t base);
+
 static void taprio_calculate_gate_durations(struct taprio_sched *q,
 					    struct sched_gate_list *sched)
 {
@@ -919,6 +926,7 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
 	struct sched_entry *entry, *next;
 	struct Qdisc *sch = q->root;
 	ktime_t end_time;
+	ktime_t basenow;
 	int tc;
 
 	spin_lock(&q->current_entry_lock);
@@ -977,6 +985,23 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
 	taprio_set_budgets(q, oper, next);
 
 first_run:
+	basenow = ktime_get();
+	if (ktime_before(end_time, basenow))
+	{
+		next->num_schedules_before_now++;
+		if (next->num_schedules_before_now >= TAPRIO_MAX_NUM_SCHEDULES_BEFORE_NOW)
+		{
+			end_time = ktime_add_ns(basenow, oper->cycle_time);
+			next->end_time = end_time;
+			next->num_schedules_before_now = 0;
+			setup_txtime(q, oper, basenow);
+		}
+	}
+	else
+	{
+		next->num_schedules_before_now = 0;
+	}
+
 	rcu_assign_pointer(q->current_entry, next);
 	spin_unlock(&q->current_entry_lock);
 
@@ -1074,6 +1099,7 @@ static int parse_sched_entry(struct taprio_sched *q, struct nlattr *n,
 	}
 
 	entry->index = index;
+	entry->num_schedules_before_now = 0;
 
 	return fill_sched_entry(q, tb, entry, extack);
 }
-- 
2.43.0

Re: [syzbot] test

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Subject: test
Author: mukattreyee@gmail.com

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

Re: [syzbot] Test

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Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git fe46a7dd189e25604716c03576d05ac8a5209743

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

Re: [syzbot] Test

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Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git dccb07f2914cdab2ac3a5b6c98406f765acab803

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

Re: [syzbot] Test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test 

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

Re: [syzbot] test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: test
Author: danielyangkang@gmail.com

#syz test

Re: [syzbot] test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: test
Author: danielyangkang@gmail.com

#syz test