What I want to ask is, what is the condition that can trigger system rebooting?
On iOS the system will automatically reboot if the kernel panics, which seems like the most likely cause of the problem you’re seeing.
Kernel panics are always bugworthy. It sounds like this panic is relatively easy to reproduce, and such bug reports are especially useful. Please do file a bug report about this, and post your bug number, just for the record.
Besides, we've got two log file after the devices rebooted.
The second log is interesting because it actually contains a traditional kernel panic log. I undid the JSON encoding and pasted the resulting log in at the end of this post.
I’m not familiar with this panic myself but the main message, “mbuf_watchdog: 8 waiters stuck for 10 secs”, is relatively easy to understand. In the context of the kernel, an
mbuf
is a memory buffer used by the networking subsystem. It seems that something has run the kernel out of these buffers, to the point where 8 threads have been waiting for memory buffers for 10 seconds. This is clearly too long, and so a watchdog has panicked the system.
The underlying cause of this could be a leak in the kernel, or there could be a bug that’s causing the kernel to over commit to work coming in from user space. Regardless, kernel panics are most definitely Apple’s problem to resolve.
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Apple Developer Relations, Developer Technical Support, Core OS/Hardware
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panic(cpu 1 caller 0xfffffff01b276c90): mbuf_watchdog: 8 waiters stuck for 10 secs
2432/2432 mbufs in use:
2432 mbufs allocated to data
820/832 mbuf 2KB clusters in use
168/168 mbuf 4KB clusters in use
1366/1366 mbuf 16KB clusters in use
25141 KB allocated to network (approx. 99% in use)
0 KB returned to the system
VM allocation failures: contiguous 0, normal 0, one page 0
worker thread runs: 99, expansions: 0, cl 7/2506, bigcl 0/0, 16k 91/1951
worker thread last run time: 118 (11 seconds ago)
mbuf leak detection table:
total captured: 323 (one per 500)
total allocs outstanding: 12
new hash recorded: 257 allocs, 234 traces
hash collisions: 4 allocs, 54 traces
overwrites: 76 allocs, 0 traces
lock conflicts: 0
top 5 outstanding traces:
[1] 5 outstanding alloc(s), 63 hit(s), 53 collision(s)
[2] 1 outstanding alloc(s), 1 hit(s), 0 collision(s)
[3] 1 outstanding alloc(s), 2 hit(s), 0 collision(s)
[4] 1 outstanding alloc(s), 1 hit(s), 0 collision(s)
[5] 1 outstanding alloc(s), 1 hit(s), 0 collision(s)
trace [1] trace [2] trace [3] trace [4] trace [5]
------------------ ------------------ ------------------ ------------------ ------------------
1: 0xfffffff007475338 0xfffffff007475338 0xfffffff007475338 0xfffffff007475338 0xfffffff007475338
2: 0xfffffff0074509ac 0xfffffff0074509ac 0xfffffff0074508d0 0xfffffff0074509ac 0xfffffff0074509ac
3: 0xfffffff007473a5c 0xfffffff00747863c 0xfffffff00747b5d0 0xfffffff007473a5c 0xfffffff007473a5c
4: 0xfffffff007450658 0xfffffff00730b6d4 0xfffffff00744a448 0xfffffff007450658 0xfffffff007450658
5: 0xfffffff00747a5c4 0xfffffff00746e9a0 0xfffffff006c7ae54 0xfffffff00747a5c4 0xfffffff00747b5d0
6: 0xfffffff007484e98 0xfffffff007321a98 0xfffffff006c7ac14 0xfffffff007484ef0 0xfffffff00744a448
7: 0xfffffff00745b974 0xfffffff00746e208 0xfffffff006c84210 0xfffffff00745b974 0xfffffff006c7ae54
8: 0xfffffff007454490 0xfffffff0073efde0 0xfffffff006c83ef4 0xfffffff007454490 0xfffffff006c7ac14
9: 0xfffffff00745429c 0xfffffff00711dc98 0xfffffff00755e3c0 0xfffffff00745429c 0xfffffff006c84210
10: 0xfffffff0071e5344 0xfffffff00755dcf4 0xfffffff0071e5344 0xfffffff006c83ef4
11: 0xfffffff0070cc1e0 0xfffffff0070cc1e0 0xfffffff00755e3c0
12: 0xfffffff00755dcf4
13:
14:
15:
16:
Debugger message: panic
Memory ID: 0x6
OS version: 15B93
Kernel version: Darwin Kernel Version 17.2.0: Fri Sep 29 18:14:51 PDT 2017; root:xnu-4570.20.62~4/RELEASE_ARM64_T8015
KernelCache UUID: FCA87F3FF353542AC8D28C3CC0E066DC
iBoot version: iBoot-4076.20.48
secure boot?: YES
Paniclog version: 8
Kernel slide: 0x0000000013e00000
Kernel text base: 0xfffffff01ae04000
Epoch Time: sec usec
Boot : 0x5a1d0932 0x0001bc4b
Sleep : 0x00000000 0x00000000
Wake : 0x00000000 0x00000000
Calendar: 0x5a1d09aa 0x0008fdd2
Panicked task 0xffffffe00078b610: 15244 pages, 263 threads: pid 0: kernel_task
Panicked thread: 0xffffffe000bb8a40, backtrace: 0xffffffe0e6f7ae20, tid: 643
lr: 0xfffffff01afe4d94 fp: 0xffffffe0e6f7af60
lr: 0xfffffff01aecc1e0 fp: 0xffffffe0e6f7af70
lr: 0xfffffff01aefa78c fp: 0xffffffe0e6f7b2e0
lr: 0xfffffff01aefaa9c fp: 0xffffffe0e6f7b320
lr: 0xfffffff01aefa93c fp: 0xffffffe0e6f7b340
lr: 0xfffffff01b276c90 fp: 0xffffffe0e6f7b530
lr: 0xfffffff01b274230 fp: 0xffffffe0e6f7b600
lr: 0xfffffff01b250658 fp: 0xffffffe0e6f7b6b0
lr: 0xfffffff01b2739dc fp: 0xffffffe0e6f7b780
lr: 0xfffffff01b250658 fp: 0xffffffe0e6f7b830
lr: 0xfffffff01b27b5d0 fp: 0xffffffe0e6f7b910
lr: 0xfffffff01b24a448 fp: 0xffffffe0e6f7b940
lr: 0xfffffff019f50f54 fp: 0xffffffe0e6f7b9a0
lr: 0xfffffff01aa8aa94 fp: 0xffffffe0e6f7ba10
lr: 0xfffffff01aa8a97c fp: 0xffffffe0e6f7baa0
lr: 0xfffffff01b360f34 fp: 0xffffffe0e6f7bb10
lr: 0xfffffff01a1b8f54 fp: 0xffffffe0e6f7bb30
lr: 0xfffffff01a6729d4 fp: 0xffffffe0e6f7bb90
lr: 0xfffffff01a6723ac fp: 0xffffffe0e6f7bbf0
lr: 0xfffffff01b35f8f4 fp: 0xffffffe0e6f7bc30
lr: 0xfffffff01b35e3c0 fp: 0xffffffe0e6f7bc60
lr: 0xfffffff01b35dcf4 fp: 0xffffffe0e6f7bc90
lr: 0xfffffff01aed4600 fp: 0x0000000000000000
