Hello,
The following program causes either division error or hangs kernel:
https://gist.githubusercontent.com/dvyukov/b1f33be3bfcc15d629e10db483bee1e4/...
divide error: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN Dumping ftrace buffer: (ftrace buffer empty) Modules linked in: CPU: 1 PID: 27320 Comm: syz-executor Not tainted 4.8.0-rc3-next-20160825+ #8 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 task: ffff88003c9b2280 task.stack: ffff880027280000 RIP: 0010:[<ffffffff858e1a6c>] [< inline >] ktime_divns include/linux/ktime.h:195 RIP: 0010:[<ffffffff858e1a6c>] [<ffffffff858e1a6c>] snd_hrtimer_callback+0x1bc/0x3c0 sound/core/hrtimer.c:62 RSP: 0018:ffff88003ed07dd8 EFLAGS: 00010006 RAX: 0000000000004801 RBX: ffff88003d3a0a88 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffff88003d3a0aa0 RDI: ffffffff886b69a8 RBP: ffff88003ed07e30 R08: 0000010e85417665 R09: ffff88007fff7048 R10: ffff88007fff7058 R11: ffff88007fff7050 R12: ffff88003d00f840 R13: ffff88003d00f8f4 R14: ffff88003d00f970 R15: ffff88003d3a0a80 FS: 0000000000000000(0000) GS:ffff88003ed00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f4152126db8 CR3: 000000006b896000 CR4: 00000000000006e0 DR0: 000000000000001e DR1: 000000000000001e DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600 Stack: 0000000000000000 ffff88003d3a0aa0 ffff88003d00f8f8 0000000000004801 ffff88003d3a0ae0 0000000000000000 ffff88003d3a0a88 0000000000000001 ffff88003ed1b400 dffffc0000000000 0000000000000001 ffff88003ed07f28 Call Trace: <IRQ> [< inline >] __run_hrtimer kernel/time/hrtimer.c:1238 [<ffffffff81504335>] __hrtimer_run_queues+0x325/0xe70 kernel/time/hrtimer.c:1302 [<ffffffff81506ceb>] hrtimer_interrupt+0x18b/0x420 kernel/time/hrtimer.c:1336 [<ffffffff8126d8df>] local_apic_timer_interrupt+0x6f/0xe0 arch/x86/kernel/apic/apic.c:933 [<ffffffff86e13056>] smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:957 [<ffffffff86e1210c>] apic_timer_interrupt+0x8c/0xa0 arch/x86/entry/entry_64.S:487 <EOI> [< inline >] rcu_lock_release include/linux/rcupdate.h:494 [< inline >] rcu_read_unlock include/linux/rcupdate.h:927 [<ffffffff81839f55>] unlock_page_memcg+0x95/0x130 mm/memcontrol.c:1680 [< inline >] page_remove_file_rmap mm/rmap.c:1343 [<ffffffff817b742c>] page_remove_rmap+0x1cc/0x8e0 mm/rmap.c:1394 [< inline >] zap_pte_range mm/memory.c:1170 [< inline >] zap_pmd_range mm/memory.c:1257 [< inline >] zap_pud_range mm/memory.c:1278 [<ffffffff81789119>] unmap_page_range+0xf89/0x1ba0 mm/memory.c:1299 [<ffffffff81789e31>] unmap_single_vma+0x101/0x260 mm/memory.c:1344 [<ffffffff8178a741>] unmap_vmas+0xf1/0x1b0 [<ffffffff817a5aab>] exit_mmap+0x22b/0x420 mm/mmap.c:2787 [< inline >] __mmput kernel/fork.c:770 [<ffffffff8137c576>] mmput+0xd6/0x3c0 kernel/fork.c:790 [< inline >] exit_mm kernel/exit.c:512 [<ffffffff813940e8>] do_exit+0x738/0x2e70 kernel/exit.c:815 [<ffffffff81396998>] do_group_exit+0x108/0x330 kernel/exit.c:958 [<ffffffff813ba4aa>] get_signal+0x62a/0x15d0 kernel/signal.c:2307 [<ffffffff81202333>] do_signal+0x83/0x1f60 arch/x86/kernel/signal.c:805 [<ffffffff81006345>] exit_to_usermode_loop+0x1a5/0x210 arch/x86/entry/common.c:163 [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:198 [< inline >] syscall_return_slowpath arch/x86/entry/common.c:267 [<ffffffff81008be0>] do_syscall_64+0x4c0/0x640 arch/x86/entry/common.c:293 [<ffffffff86e107c3>] entry_SYSCALL64_slow_path+0x25/0x25 Code: cb a2 ce fb 8b 0d f5 21 70 05 48 0f af 4d d0 48 85 c9 0f 88 6a 01 00 00 48 89 4d a8 e8 ae a2 ce fb 48 8b 45 c0 48 8b 4d a8 48 99 <48> f7 f9 48 01 45 d0 e8 98 a2 ce fb 4c 89 fa 48 b8 00 00 00 00 RIP [< inline >] ktime_divns include/linux/ktime.h:195 RIP [<ffffffff858e1a6c>] snd_hrtimer_callback+0x1bc/0x3c0 sound/core/hrtimer.c:62 RSP <ffff88003ed07dd8> ---[ end trace e1a6d1e5a6136d50 ]---
or:
INFO: rcu_sched detected stalls on CPUs/tasks: 0-...: (1 GPs behind) idle=203/140000000000001/0 softirq=923090/923091 fqs=6490 (detected by 1, t=26002 jiffies, g=508022, c=508021, q=20) Task dump for CPU 0: a.out R running task 28848 31756 4047 0x0000000a 0000000000000000 0000000000000282 0000000000000000 ffff880066a9b430 ffff880066a9b430 ffff8800667cfae0 0000000000000282 0000000000000000 0000000000000000 0000000000000000 000003a0184674dd dffffc0000000000 Call Trace: [< inline >] spin_unlock_irqrestore ./include/linux/spinlock.h:362 [<ffffffff858db3dd>] snd_timer_start1+0xdd/0x740 sound/core/timer.c:477 [<ffffffff858dbb25>] snd_timer_continue+0x45/0x80 sound/core/timer.c:606 [< inline >] snd_timer_user_continue sound/core/timer.c:1835 [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1902 [<ffffffff858df299>] snd_timer_user_ioctl+0xe99/0x2470 sound/core/timer.c:1917 [< inline >] vfs_ioctl fs/ioctl.c:43 [<ffffffff818a1dfc>] do_vfs_ioctl+0x18c/0x1080 fs/ioctl.c:675 [< inline >] SYSC_ioctl fs/ioctl.c:690 [<ffffffff818a2d7f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:681 [<ffffffff86e10700>] entry_SYSCALL_64_fastpath+0x23/0xc1 arch/x86/entry/entry_64.S:208
I am on 0f98f121e1670eaa2a2fbb675e07d6ba7f0e146f of linux-next with the following diff in sound/core/timer.c (one is a fix for another division by 0):
diff --git a/sound/core/timer.c b/sound/core/timer.c index 9a6157e..3e55c6d 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -813,6 +813,7 @@ int snd_timer_new(struct snd_card *card, char *id, struct snd_timer_id *tid, timer->tmr_subdevice = tid->subdevice; if (id) strlcpy(timer->id, id, sizeof(timer->id)); + timer->sticks = 1; INIT_LIST_HEAD(&timer->device_list); INIT_LIST_HEAD(&timer->open_list_head); INIT_LIST_HEAD(&timer->active_list_head); @@ -1958,6 +1959,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, tu->qused--; spin_unlock_irq(&tu->qlock);
+ mutex_lock(&tu->ioctl_lock); if (tu->tread) { if (copy_to_user(buffer, &tu->tqueue[qhead], sizeof(struct snd_timer_tread))) @@ -1967,6 +1969,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, sizeof(struct snd_timer_read))) err = -EFAULT; } + mutex_unlock(&tu->ioctl_lock);
spin_lock_irq(&tu->qlock); if (err < 0)