[syzbot] [kernel?] BUG: soft lockup in gate_timer_func

[syzbot] [kernel?] BUG: soft lockup in gate_timer_func

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    21d6ac051080 Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=10a50679580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d1128bc53f2ef7f3
dashboard link: https://syzkaller.appspot.com/bug?extid=0054fed3dc9085390f51
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15911a25580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com

watchdog: BUG: soft lockup - CPU#1 stuck for 3s! [syz-executor291:5020]
Modules linked in:
irq event stamp: 4562887
hardirqs last  enabled at (4562886): [<ffff800080557c84>] seqcount_lockdep_reader_access+0x7c/0xf8 include/linux/seqlock.h:75
hardirqs last disabled at (4562887): [<ffff80008690b4b4>] __el1_irq arch/arm64/kernel/entry-common.c:527 [inline]
hardirqs last disabled at (4562887): [<ffff80008690b4b4>] el1_interrupt+0x28/0x60 arch/arm64/kernel/entry-common.c:543
softirqs last  enabled at (14246): [<ffff800084c0e6c4>] __alloc_skb+0x1c0/0x610 net/core/skbuff.c:698
softirqs last disabled at (14249): [<ffff8000800204c0>] __do_softirq+0x14/0x20 kernel/softirq.c:656
CPU: 1 UID: 0 PID: 5020 Comm: syz-executor291 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/07/2026
pstate: 43400005 (nZcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : seqcount_lockdep_reader_access+0xd8/0xf8 include/linux/seqlock.h:76
lr : seqcount_lockdep_reader_access+0xd4/0xf8 include/linux/seqlock.h:75
sp : ffff80008eb77ce0
x29: ffff80008eb77ce0 x28: 1fffe00034bbc63a x27: ffff80008e853110
x26: dfff800000000000 x25: ffff0000c1b62b80 x24: 1fffe0001ad59fa6
x23: dfff800000000000 x22: ffff0000c1b62bb0 x21: 0000000000000000
x20: ffff8000805580e8 x19: 00000000000000c0 x18: 0000000000000000
x17: ffff80008a7d6000 x16: 0000000000000002 x15: ffff80008a35fda0
x14: ffff80008a5d5e28 x13: 0000000000000001 x12: ffff0000d5af8000
x11: ffff80008a5d5e28 x10: 0000000000000003 x9 : 0000000000000101
x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000008 x3 : ffff800080557cd4
x2 : 0000000000000080 x1 : ffff0000d5af8000 x0 : 0000000000000000
Call trace:
 __daif_local_irq_restore arch/arm64/include/asm/irqflags.h:175 [inline] (P)
 arch_local_irq_restore arch/arm64/include/asm/irqflags.h:195 [inline] (P)
 seqcount_lockdep_reader_access+0xd8/0xf8 include/linux/seqlock.h:75 (P)
 ktime_get+0x68/0x218 kernel/time/timekeeping.c:971
 gate_get_time+0x1c/0xa4 net/sched/act_gate.c:23
 gate_timer_func+0x1a8/0x390 net/sched/act_gate.c:101
 __run_hrtimer kernel/time/hrtimer.c:2032 [inline]
 __hrtimer_run_queues+0x314/0xbe0 kernel/time/hrtimer.c:2096
 hrtimer_run_softirq+0x15c/0x21c kernel/time/hrtimer.c:2113
 handle_softirqs+0x2ec/0xd98 kernel/softirq.c:622
 __do_softirq+0x14/0x20 kernel/softirq.c:656
 ____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:78
 call_on_irq_stack+0x30/0x48 arch/arm64/kernel/entry.S:885
 do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:83
 invoke_softirq kernel/softirq.c:503 [inline]
 __irq_exit_rcu+0x1ac/0x428 kernel/softirq.c:735
 irq_exit_rcu+0x14/0x84 kernel/softirq.c:752
 __el1_irq arch/arm64/kernel/entry-common.c:531 [inline]
 el1_interrupt+0x40/0x60 arch/arm64/kernel/entry-common.c:543
 el1h_64_irq_handler+0x18/0x24 arch/arm64/kernel/entry-common.c:548
 el1h_64_irq+0x6c/0x70 arch/arm64/kernel/entry.S:586
 __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:26 [inline] (P)
 arch_local_irq_enable arch/arm64/include/asm/irqflags.h:48 [inline] (P)
 __local_bh_enable_ip+0x1f0/0x35c kernel/softirq.c:455 (P)
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 __alloc_skb+0x1c8/0x610 net/core/skbuff.c:699
 alloc_skb include/linux/skbuff.h:1384 [inline]
 alloc_skb_with_frags+0xb8/0x690 net/core/skbuff.c:6775
 sock_alloc_send_pskb+0x740/0x850 net/core/sock.c:3012
 unix_dgram_sendmsg+0x434/0x1078 net/unix/af_unix.c:2137
 sock_sendmsg_nosec net/socket.c:775 [inline]
 __sock_sendmsg+0xc8/0x17c net/socket.c:790
 __sys_sendto+0x250/0x328 net/socket.c:2252
 __do_sys_sendto net/socket.c:2259 [inline]
 __se_sys_sendto net/socket.c:2255 [inline]
 __arm64_sys_sendto+0xec/0x10c net/socket.c:2255
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:758
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:777
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:590
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:26 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_local_irq_enable arch/arm64/include/asm/irqflags.h:48 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle_call+0xd0/0xfc kernel/sched/idle.c:129
watchdog: BUG: soft lockup - CPU#1 stuck for 6s! [syz-executor291:5020]
Modules linked in:
irq event stamp: 9755971
hardirqs last  enabled at (9755970): [<ffff800086930818>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:178 [inline]
hardirqs last  enabled at (9755970): [<ffff800086930818>] _raw_spin_unlock_irqrestore+0x38/0x98 kernel/locking/spinlock.c:198
hardirqs last disabled at (9755971): [<ffff80008690b4b4>] __el1_irq arch/arm64/kernel/entry-common.c:527 [inline]
hardirqs last disabled at (9755971): [<ffff80008690b4b4>] el1_interrupt+0x28/0x60 arch/arm64/kernel/entry-common.c:543
softirqs last  enabled at (14246): [<ffff800084c0e6c4>] __alloc_skb+0x1c0/0x610 net/core/skbuff.c:698
softirqs last disabled at (14249): [<ffff8000800204c0>] __do_softirq+0x14/0x20 kernel/softirq.c:656
CPU: 1 UID: 0 PID: 5020 Comm: syz-executor291 Tainted: G             L      syzkaller #0 PREEMPT 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/07/2026
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:179 [inline]
pc : _raw_spin_unlock_irqrestore+0x44/0x98 kernel/locking/spinlock.c:198
lr : __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:178 [inline]
lr : _raw_spin_unlock_irqrestore+0x38/0x98 kernel/locking/spinlock.c:198
sp : ffff80008eb77dc0
x29: ffff80008eb77dc0 x28: 1fffe00034bbc63a x27: ffff0001a5de31c0
x26: ffff0001a5de31d0 x25: ffff0000d6acfd38 x24: dfff800000000000
x23: 0000000000000001 x22: ffff800084ec6bfc x21: ffff0001a5de2d80
x20: ffff0001a5de2d80 x19: 0000000000000000 x18: 0000000000000000
x17: ffff80008a7d6000 x16: 0000000000000004 x15: ffff80008a35fda0
x14: 000000008030dda8 x13: 0000000000000001 x12: 0000000000000000
x11: ffff800080156070 x10: 0000000000000003 x9 : 0000000000000000
x8 : 00000000000000c0 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000008 x3 : ffff800080156118
x2 : 0000000000000000 x1 : ffff0000d5af8000 x0 : ffff80011d2fd000
Call trace:
 __daif_local_irq_restore arch/arm64/include/asm/irqflags.h:175 [inline] (P)
 arch_local_irq_restore arch/arm64/include/asm/irqflags.h:195 [inline] (P)
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:178 [inline] (P)
 _raw_spin_unlock_irqrestore+0x44/0x98 kernel/locking/spinlock.c:198 (P)
 __run_hrtimer kernel/time/hrtimer.c:2028 [inline]
 __hrtimer_run_queues+0x22c/0xbe0 kernel/time/hrtimer.c:2096
 hrtimer_run_softirq+0x15c/0x21c kernel/time/hrtimer.c:2113
 handle_softirqs+0x2ec/0xd98 kernel/softirq.c:622
 __do_softirq+0x14/0x20 kernel/softirq.c:656
 ____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:78
 call_on_irq_stack+0x30/0x48 arch/arm64/kernel/entry.S:885
 do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:83
 invoke_softirq kernel/softirq.c:503 [inline]
 __irq_exit_rcu+0x1ac/0x428 kernel/softirq.c:735
 irq_exit_rcu+0x14/0x84 kernel/softirq.c:752
 __el1_irq arch/arm64/kernel/entry-common.c:531 [inline]
 el1_interrupt+0x40/0x60 arch/arm64/kernel/entry-common.c:543
 el1h_64_irq_handler+0x18/0x24 arch/arm64/kernel/entry-common.c:548
 el1h_64_irq+0x6c/0x70 arch/arm64/kernel/entry.S:586
 __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:26 [inline] (P)
 arch_local_irq_enable arch/arm64/include/asm/irqflags.h:48 [inline] (P)
 __local_bh_enable_ip+0x1f0/0x35c kernel/softirq.c:455 (P)
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 __alloc_skb+0x1c8/0x610 net/core/skbuff.c:699
 alloc_skb include/linux/skbuff.h:1384 [inline]
 alloc_skb_with_frags+0xb8/0x690 net/core/skbuff.c:6775
 sock_alloc_send_pskb+0x740/0x850 net/core/sock.c:3012
 unix_dgram_sendmsg+0x434/0x1078 net/unix/af_unix.c:2137
 sock_sendmsg_nosec net/socket.c:775 [inline]
 __sock_sendmsg+0xc8/0x17c net/socket.c:790
 __sys_sendto+0x250/0x328 net/socket.c:2252
 __do_sys_sendto net/socket.c:2259 [inline]
 __se_sys_sendto net/socket.c:2255 [inline]
 __arm64_sys_sendto+0xec/0x10c net/socket.c:2255
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:758
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:777
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:590
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:26 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_local_irq_enable arch/arm64/include/asm/irqflags.h:48 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle_call+0xd0/0xfc kernel/sched/idle.c:129
watchdog: BUG: soft lockup - CPU#1 stuck for 9s! [syz-executor291:5020]
Modules linked in:
irq event stamp: 14939657
hardirqs last  enabled at (14939656): [<ffff800086930818>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:178 [inline]
hardirqs last  enabled at (14939656): [<ffff800086930818>] _raw_spin_unlock_irqrestore+0x38/0x98 kernel/locking/spinlock.c:198
hardirqs last disabled at (14939657): [<ffff80008690b4b4>] __el1_irq arch/arm64/kernel/entry-common.c:527 [inline]
hardirqs last disabled at (14939657): [<ffff80008690b4b4>] el1_interrupt+0x28/0x60 arch/arm64/kernel/entry-common.c:543
softirqs last  enabled at (14246): [<ffff800084c0e6c4>] __alloc_skb+0x1c0/0x610 net/core/skbuff.c:698
softirqs last disabled at (14249): [<ffff8000800204c0>] __do_softirq+0x14/0x20 kernel/softirq.c:656
CPU: 1 UID: 0 PID: 5020 Comm: syz-executor291 Tainted: G             L      syzkaller #0 PREEMPT 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/07/2026
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:179 [inline]
pc : _raw_spin_unlock_irqrestore+0x44/0x98 kernel/locking/spinlock.c:198
lr : __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:178 [inline]
lr : _raw_spin_unlock_irqrestore+0x38/0x98 kernel/locking/spinlock.c:198
sp : ffff80008eb77dc0
x29: ffff80008eb77dc0 x28: 1fffe00034bbc63a x27: ffff0001a5de31c0
x26: ffff0001a5de31d0 x25: ffff0000d6acfd38 x24: dfff800000000000
x23: 0000000000000001 x22: ffff800084ec6bfc x21: ffff0001a5de2d80
x20: ffff0001a5de2d80 x19: 0000000000000000 x18: 0000000000000000
x17: ffff80008a7d6000 x16: 0000000000000004 x15: ffff80008a35fda0
x14: 000000008030dda8 x13: 0000000000000001 x12: 0000000000000000
x11: ffff800080156070 x10: 0000000000000003 x9 : 0000000000000000
x8 : 00000000000000c0 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000008 x3 : ffff800080156118
x2 : 0000000000000000 x1 : ffff0000d5af8000 x0 : ffff80011d2fd000
Call trace:
 __daif_local_irq_restore arch/arm64/include/asm/irqflags.h:175 [inline] (P)
 arch_local_irq_restore arch/arm64/include/asm/irqflags.h:195 [inline] (P)
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:178 [inline] (P)
 _raw_spin_unlock_irqrestore+0x44/0x98 kernel/locking/spinlock.c:198 (P)
 __run_hrtimer kernel/time/hrtimer.c:2028 [inline]
 __hrtimer_run_queues+0x22c/0xbe0 kernel/time/hrtimer.c:2096
 hrtimer_run_softirq+0x15c/0x21c kernel/time/hrtimer.c:2113
 handle_softirqs+0x2ec/0xd98 kernel/softirq.c:622
 __do_softirq+0x14/0x20 kernel/softirq.c:656
 ____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:78
 call_on_irq_stack+0x30/0x48 arch/arm64/kernel/entry.S:885
 do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:83
 invoke_softirq kernel/softirq.c:503 [inline]
 __irq_exit_rcu+0x1ac/0x428 kernel/softirq.c:735
 irq_exit_rcu+0x14/0x84 kernel/softirq.c:752
 __el1_irq arch/arm64/kernel/entry-common.c:531 [inline]
 el1_interrupt+0x40/0x60 arch/arm64/kernel/entry-common.c:543
 el1h_64_irq_handler+0x18/0x24 arch/arm64/kernel/entry-common.c:548
 el1h_64_irq+0x6c/0x70 arch/arm64/kernel/entry.S:586
 __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:26 [inline] (P)
 arch_local_irq_enable arch/arm64/include/asm/irqflags.h:48 [inline] (P)
 __local_bh_enable_ip+0x1f0/0x35c kernel/softirq.c:455 (P)
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 __alloc_skb+0x1c8/0x610 net/core/skbuff.c:699
 alloc_skb include/linux/skbuff.h:1384 [inline]
 alloc_skb_with_frags+0xb8/0x690 net/core/skbuff.c:6775
 sock_alloc_send_pskb+0x740/0x850 net/core/sock.c:3012
 unix_dgram_sendmsg+0x434/0x1078 net/unix/af_unix.c:2137
 sock_sendmsg_nosec net/socket.c:775 [inline]
 __sock_sendmsg+0xc8/0x17c net/socket.c:790
 __sys_sendto+0x250/0x328 net/socket.c:2252
 __do_sys_sendto net/socket.c:2259 [inline]
 __se_sys_sendto net/socket.c:2255 [inline]
 __arm64_sys_sendto+0xec/0x10c net/socket.c:2255
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:758
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:777
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:590
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:26 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_local_irq_enable arch/arm64/include/asm/irqflags.h:48 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle_call+0xd0/0xfc kernel/sched/idle.c:129
watchdog: BUG: soft lockup - CPU#1 stuck for 12s! [syz-executor291:5020]
Modules linked in:
irq event stamp: 20130019
hardirqs last  enabled at (20130018): [<ffff800086930818>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:178 [inline]
hardirqs last  enabled at (20130018): [<ffff800086930818>] _raw_spin_unlock_irqrestore+0x38/0x98 kernel/locking/spinlock.c:198
hardirqs last disabled at (20130019): [<ffff80008690b4b4>] __el1_irq arch/arm64/kernel/entry-common.c:527 [inline]
hardirqs last disabled at (20130019): [<ffff80008690b4b4>] el1_interrupt+0x28/0x60 arch/arm64/kernel/entry-common.c:543
softirqs last  enabled at (14246): [<ffff800084c0e6c4>] __alloc_skb+0x1c0/0x610 net/core/skbuff.c:698
softirqs last disabled at (14249): [<ffff8000800204c0>] __do_softirq+0x14/0x20 kernel/softirq.c:656
CPU: 1 UID: 0 PID: 5020 Comm: syz-executor291 Tainted: G             L      syzkaller #0 PREEMPT 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/07/2026
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:179 [inline]
pc : _raw_spin_unlock_irqrestore+0x44/0x98 kernel/locking/spinlock.c:198
lr : __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:178 [inline]
lr : _raw_spin_unlock_irqrestore+0x38/0x98 kernel/locking/spinlock.c:198
sp : ffff80008eb77dc0
x29: ffff80008eb77dc0 x28: 1fffe00034bbc63a x27: ffff0001a5de31c0
x26: ffff0001a5de31d0 x25: ffff0000d6acfd38 x24: dfff800000000000
x23: 0000000000000001 x22: ffff800084ec6bfc x21: ffff0001a5de2d80
x20: ffff0001a5de2d80 x19: 0000000000000000 x18: 0000000000000000
x17: ffff80008a7d6000 x16: 0000000000000004 x15: ffff80008a35fda0
x14: 000000008030dda8 x13: 0000000000000001 x12: 0000000000000000
x11: ffff800080156070 x10: 0000000000000003 x9 : 0000000000000000
x8 : 00000000000000c0 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000008 x3 : ffff800080156118
x2 : 0000000000000000 x1 : ffff0000d5af8000 x0 : ffff80011d2fd000
Call trace:
 __daif_local_irq_restore arch/arm64/include/asm/irqflags.h:175 [inline] (P)
 arch_local_irq_restore arch/arm64/include/asm/irqflags.h:195 [inline] (P)
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:178 [inline] (P)
 _raw_spin_unlock_irqrestore+0x44/0x98 kernel/locking/spinlock.c:198 (P)
 __run_hrtimer kernel/time/hrtimer.c:2028 [inline]
 __hrtimer_run_queues+0x22c/0xbe0 kernel/time/hrtimer.c:2096
 hrtimer_run_softirq+0x15c/0x21c kernel/time/hrtimer.c:2113
 handle_softirqs+0x2ec/0xd98 kernel/softirq.c:622
 __do_softirq+0x14/0x20 kernel/softirq.c:656
 ____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:78
 call_on_irq_stack+0x30/0x48 arch/arm64/kernel/entry.S:885
 do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:83
 invoke_softirq kernel/softirq.c:503 [inline]
 __irq_exit_rcu+0x1ac/0x428 kernel/softirq.c:735
 irq_exit_rcu+0x14/0x84 kernel/softirq.c:752
 __el1_irq arch/arm64/kernel/entry-common.c:531 [inline]
 el1_interrupt+0x40/0x60 arch/arm64/kernel/entry-common.c:543
 el1h_64_irq_handler+0x18/0x24 arch/arm64/kernel/entry-common.c:548
 el1h_64_irq+0x6c/0x70 arch/arm64/kernel/entry.S:586
 __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:26 [inline] (P)
 arch_local_irq_enable arch/arm64/include/asm/irqflags.h:48 [inline] (P)
 __local_bh_enable_ip+0x1f0/0x35c kernel/softirq.c:455 (P)
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 __alloc_skb+0x1c8/0x610 net/core/skbuff.c:699
 alloc_skb include/linux/skbuff.h:1384 [inline]
 alloc_skb_with_frags+0xb8/0x690 net/core/skbuff.c:6775
 sock_alloc_send_pskb+0x740/0x850 net/core/sock.c:3012
 unix_dgram_sendmsg+0x434/0x1078 net/unix/af_unix.c:2137
 sock_sendmsg_nosec net/socket.c:775 [inline]
 __sock_sendmsg+0xc8/0x17c net/socket.c:790
 __sys_sendto+0x250/0x328 net/socket.c:2252
 __do_sys_sendto net/socket.c:2259 [inline]
 __se_sys_sendto net/socket.c:2255 [inline]
 __arm64_sys_sendto+0xec/0x10c net/socket.c:2255
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:758
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:777
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:590
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:26 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_local_irq_enable arch/arm64/include/asm/irqflags.h:48 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle_call+0xd0/0xfc kernel/sched/idle.c:129


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

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.

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If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [kernel?] BUG: soft lockup in gate_timer_func

[Edward Adam Davis]

#syz test

diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c
index fdbfcaa3e2ab..9065e7b88156 100644
--- a/net/sched/act_gate.c
+++ b/net/sched/act_gate.c
@@ -88,7 +88,8 @@ static enum hrtimer_restart gate_timer_func(struct hrtimer *timer)
 	gact->current_max_octets = next->maxoctets;
 
 	gact->current_close_time = ktime_add_ns(gact->current_close_time,
-						next->interval);
+						next->interval < 100 ?
+						100 : next->interval);
 
 	close_time = gact->current_close_time;
 
@@ -101,10 +102,10 @@ static enum hrtimer_restart gate_timer_func(struct hrtimer *timer)
 	now = gate_get_time(gact);
 
 	if (ktime_after(now, close_time)) {
-		ktime_t cycle, base;
+		u64 cycle, base;
 		u64 n;
 
-		cycle = p->tcfg_cycletime;
+		cycle = p->tcfg_cycletime > 20 ? 20 : p->tcfg_cycletime;
 		base = ns_to_ktime(p->tcfg_basetime);
 		n = div64_u64(ktime_sub_ns(now, base), cycle);
 		close_time = ktime_add_ns(base, (n + 1) * cycle);

Re: [syzbot] [kernel?] BUG: soft lockup in gate_timer_func

[syzbot]

Hello,

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

Reported-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com
Tested-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com

Tested on:

commit:         21d6ac05 Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=12e79a25580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d1128bc53f2ef7f3
dashboard link: https://syzkaller.appspot.com/bug?extid=0054fed3dc9085390f51
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1653e679580000

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

Re: [syzbot] [kernel?] BUG: soft lockup in gate_timer_func

[Edward Adam Davis]

#syz test

diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c
index fdbfcaa3e2ab..6b8adfbf9c2d 100644
--- a/net/sched/act_gate.c
+++ b/net/sched/act_gate.c
@@ -178,6 +178,10 @@ static const struct nla_policy gate_policy[TCA_GATE_MAX + 1] = {
 	[TCA_GATE_CLOCKID]		= { .type = NLA_S32 },
 };
 
+#ifndef __NET_TC_GATE_LIMIT
+#define GATE_ENTRY_INTERVAL_MIN 100
+#endif
+
 static int fill_gate_entry(struct nlattr **tb, struct tcfg_gate_entry *entry,
 			   struct netlink_ext_ack *extack)
 {
@@ -188,7 +192,7 @@ static int fill_gate_entry(struct nlattr **tb, struct tcfg_gate_entry *entry,
 	if (tb[TCA_GATE_ENTRY_INTERVAL])
 		interval = nla_get_u32(tb[TCA_GATE_ENTRY_INTERVAL]);
 
-	if (interval == 0) {
+	if (interval < GATE_ENTRY_INTERVAL_MIN) {
 		NL_SET_ERR_MSG(extack, "Invalid interval for schedule entry");
 		return -EINVAL;
 	}

Re: [syzbot] [kernel?] BUG: soft lockup in gate_timer_func

[syzbot]

Hello,

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

Reported-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com
Tested-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com

Tested on:

commit:         21d6ac05 Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=11685a25580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d1128bc53f2ef7f3
dashboard link: https://syzkaller.appspot.com/bug?extid=0054fed3dc9085390f51
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64
patch:          https://syzkaller.appspot.com/x/patch.diff?x=150076c6580000

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

Re: [syzbot] [kernel?] BUG: soft lockup in gate_timer_func

[Edward Adam Davis]

#syz test

diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c
index fdbfcaa3e2ab..ad5a6d75bbda 100644
--- a/net/sched/act_gate.c
+++ b/net/sched/act_gate.c
@@ -501,6 +501,8 @@ static int tcf_gate_init(struct net *net, struct nlattr *nla,
 			cycle = ktime_add_ns(cycle, entry->interval);
 		cycletime = cycle;
 	}
+	if (cycletime > S64_MAX)
+		cycletime = S64_MAX;
 	p->tcfg_cycletime = cycletime;
 	p->tcfg_cycletime_ext = cycletime_ext;
 

Re: [syzbot] [kernel?] BUG: soft lockup in gate_timer_func

[syzbot]

Hello,

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

Reported-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com
Tested-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com

Tested on:

commit:         21d6ac05 Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=10fc1679580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d1128bc53f2ef7f3
dashboard link: https://syzkaller.appspot.com/bug?extid=0054fed3dc9085390f51
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17b73679580000

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

[PATCH] net/sched: act_gate: Limit the max value for cycletime

[Edward Adam Davis]

If the user passes a cycletime value of 0xFFFFFFFFFFFFFFFFULL,
an overflow occurs during the assignment of cycle in gate_timer_func():

cycle = p->tcfg_cycletime; // overflow, cycle = -1

Since the local variable cycle is declared as ktime_t (i.e., s64),
the assignment overflows.

This leads to an incorrect calculation of the close_time value.
Ultimately, the new hrtimer expiry time becomes less than now, causing
__hrtimer_run_queues() to execute the "timer callback" for an excessively
long period, which triggers a soft lockup. [1]

Another factor is that the passed interval value is 1; while this accelerates
the problematic progression of close_time, it is not the decisive factor in
the issue described in [1].

When initializing cycletime, ensuring its value does not exceed S64_MAX
guarantees that the hrtimer can correctly calculate a valid expiry time.

[1]
watchdog: BUG: soft lockup - CPU#1 stuck for 3s! [syz-executor291:5020]
pc : seqcount_lockdep_reader_access+0xd8/0xf8 include/linux/seqlock.h:76
Call trace:
 arch_local_irq_restore arch/arm64/include/asm/irqflags.h:195 [inline] (P)
 seqcount_lockdep_reader_access+0xd8/0xf8 include/linux/seqlock.h:75 (P)
 ktime_get+0x68/0x218 kernel/time/timekeeping.c:971
 gate_get_time+0x1c/0xa4 net/sched/act_gate.c:23
 gate_timer_func+0x1a8/0x390 net/sched/act_gate.c:101
 __run_hrtimer kernel/time/hrtimer.c:2032 [inline]
 __hrtimer_run_queues+0x314/0xbe0 kernel/time/hrtimer.c:2096
 hrtimer_run_softirq+0x15c/0x21c kernel/time/hrtimer.c:2113
 handle_softirqs+0x2ec/0xd98 kernel/softirq.c:622
 __do_softirq+0x14/0x20 kernel/softirq.c:656
 ____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:78
 call_on_irq_stack+0x30/0x48 arch/arm64/kernel/entry.S:885
 do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:83
 invoke_softirq kernel/softirq.c:503 [inline]
 __irq_exit_rcu+0x1ac/0x428 kernel/softirq.c:735
 irq_exit_rcu+0x14/0x84 kernel/softirq.c:752
 __el1_irq arch/arm64/kernel/entry-common.c:531 [inline]
 el1_interrupt+0x40/0x60 arch/arm64/kernel/entry-common.c:543
 el1h_64_irq_handler+0x18/0x24 arch/arm64/kernel/entry-common.c:548
 el1h_64_irq+0x6c/0x70 arch/arm64/kernel/entry.S:586
 __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:26 [inline] (P)
 arch_local_irq_enable arch/arm64/include/asm/irqflags.h:48 [inline] (P)
 __local_bh_enable_ip+0x1f0/0x35c kernel/softirq.c:455 (P)
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 __alloc_skb+0x1c8/0x610 net/core/skbuff.c:699
 alloc_skb include/linux/skbuff.h:1384 [inline]
 alloc_skb_with_frags+0xb8/0x690 net/core/skbuff.c:6775
 sock_alloc_send_pskb+0x740/0x850 net/core/sock.c:3012
 unix_dgram_sendmsg+0x434/0x1078 net/unix/af_unix.c:2137
 sock_sendmsg_nosec net/socket.c:775 [inline]

Fixes: a51c328df310 ("net: qos: introduce a gate control flow action")
Reported-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=0054fed3dc9085390f51
Tested-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 net/sched/act_gate.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c
index fdbfcaa3e2ab..ad5a6d75bbda 100644
--- a/net/sched/act_gate.c
+++ b/net/sched/act_gate.c
@@ -501,6 +501,8 @@ static int tcf_gate_init(struct net *net, struct nlattr *nla,
 			cycle = ktime_add_ns(cycle, entry->interval);
 		cycletime = cycle;
 	}
+	if (cycletime > S64_MAX)
+		cycletime = S64_MAX;
 	p->tcfg_cycletime = cycletime;
 	p->tcfg_cycletime_ext = cycletime_ext;
 
-- 
2.43.0