On 30/10/2018 09:26, Peter Zijlstra wrote:
On Tue, Oct 23, 2018 at 11:30:11AM +0100, John Garry wrote:
Hi all,
I have stumbled upon this crash on my arm64 system:
[ 7.040874] SMP: Total of 64 processors activated.
[ 7.045720] CPU features: detected: GIC system register CPU interface
[ 7.052240] CPU features: detected: 32-bit EL0 Support
[ 7.144026] CPU: All CPU(s) started at EL2
[ 7.148298] alternatives: patching kernel code
[ 7.155277] Unable to handle kernel NULL pointer dereference at virtual
address 0000000000000000
[ 7.164163] Mem abort info:
[ 7.166978] ESR = 0x96000004
[ 7.170061] Exception class = DABT (current EL), IL = 32 bits
[ 7.176043] SET = 0, FnV = 0
[ 7.179121] EA = 0, S1PTW = 0
[ 7.182291] Data abort info:
[ 7.185193] ISV = 0, ISS = 0x00000004
[ 7.189066] CM = 0, WnR = 0
[ 7.192056] [0000000000000000] user address but active_mm is swapper
[ 7.198480] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[ 7.204107] Modules linked in:
[ 7.207189] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W
4.19.0-00002-g3ed52fd-dirty #807
[ 7.216596] Hardware name: Hisilicon Hip07 D05 Development Board (DT)
[ 7.223102] pstate: 20000005 (nzCv daif -PAN -UAO)
[ 7.227946] pc : __ll_sc_atomic_sub_return+0x4/0x20
[ 7.232873] lr : free_sched_groups.part.1+0x40/0x98
[ 7.237797] sp : ffff00000947bc60
[ 7.241138] x29: ffff00000947bc60 x28: ffff801fb49ba000
[ 7.246504] x27: ffff000009109b38 x26: ffff801fb4a38000
[ 7.251869] x25: ffff801fb48cc000 x24: ffff000009109000
[ 7.257235] x23: 0000000000000010 x22: 0000000000000001
[ 7.262599] x21: ffff801fb4a0b000 x20: ffff801fb4a65f00
[ 7.267964] x19: ffff801fb4a65f80 x18: 0000000000000400
[ 7.273329] x17: 00000000ffffffff x16: 0000000000000000
[ 7.278694] x15: ffff801ffbffef80 x14: ffff7e007ed14bc0
[ 7.284059] x13: 00000000000000c0 x12: 000000000000003f
[ 7.289423] x11: ffff801fb62258b8 x10: 0000000000000001
[ 7.294788] x9 : ffff801fb44b0100 x8 : 000000000000000f
[ 7.300153] x7 : ffff801fb48b1900 x6 : 0000801ff2efb000
[ 7.305518] x5 : ffff0000091096f0 x4 : 0000000000000400
[ 7.310882] x3 : ffff801fb4a65000 x2 : ffff801fb4a0b000
[ 7.316247] x1 : 0000000000000000 x0 : 0000000000000001
[ 7.321613] Process swapper/0 (pid: 1, stack limit = 0x(____ptrval____))
[ 7.328382] Call trace:
[ 7.330847] __ll_sc_atomic_sub_return+0x4/0x20
[ 7.335420] destroy_sched_domain+0x20/0x70
[ 7.339642] cpu_attach_domain+0xc8/0x2e8
[ 7.343687] build_sched_domains+0xd44/0xde0
[ 7.347996] sched_init_domains+0x68/0x88
[ 7.352044] sched_init_smp+0x2c/0x7c
[ 7.355738] kernel_init_freeable+0xdc/0x244
[ 7.360049] kernel_init+0x10/0x108
[ 7.363567] ret_from_fork+0x10/0x18
[ 7.367174] Code: 88107c31 35ffffb0 d65f03c0 f9800031 (885f7c31)
[ 7.373400] ---[ end trace 8150af869a14363f ]---
[ 7.378076] Kernel panic - not syncing: Attempted to kill init!
exitcode=0x0000000b
[ 7.378076]
[ 7.387320] SMP: stopping secondary CPUs
[ 7.391297] ---[ end Kernel panic - not syncing: Attempted to kill init!
exitcode=0x0000000b
[ 7.391297] ]---
I will straightaway note that I have been fiddling with my board's device
tree, specifically (breaking!) the NUMA distance map, like this:
distance-matrix = <0 0 10>,
<0 1 15>,
<0 2 20>,
<0 3 25>,
<1 0 15>,
<1 1 10>,
<1 2 25>,
<1 3 30>,
<2 0 20>,
<2 1 25>,
<2 2 10>,
<2 3 15>,
<3 0 10>,* should be same as 0->3 and > 10
<3 1 10>,* should be same as 1->3 and > 10
<3 2 15>,
<3 3 15>;* should be 10
However I don't think that this should crash the kernel. I'd say
of_numa_parse_distance_map_v1() should robustly handle broken maps, probably
by erroring and causing NUMA to be disabled.
If build with CONFIG_SCHED_DEBUG=y and boot with "sched_debug" I think
sched_init_numa() should yell at you for the above 'mistake'.
Right, I have since turned on debug and it was complaining - I'll
provide a log.
However I am interested to know if the scheduler crash is a real problem.
Ideally we'd not crash of course.. let me see if I can still make sense
of that topology code.
JFYI, https://lkml.org/lkml/2018/10/26/527
So it seems to be that setting the distance between separate nodes to
LOCAL_DISTANCE causes the problem. x86 NUMA code - like arm64 - allows
this. However ACPI SLIT validation rejects this, unlike OF distance map
parsing.
Thanks,
John
