------- Comment From kla...@br.ibm.com 2018-04-24 10:42 EDT------- (In reply to comment #166) > this point, I don't see a connection to KVM or even Ubuntu vs. Pegas. This > appears to be something that will happen in any distro that has the right > vintage of qla2xxx driver. Not sure why we think this did not happen on > Ubuntu -13 kernel - I see nothing in the diffs of qla2xxx that would affect > this.
What is puzzling is that we had multiple reproduces (with guests, without guests) prior to Dwip's patch. With Dwip's patch, which is arguably not covering all scenarios, we didn't get any repro Without Dwip's patch, but reverting 165988, so far it looks clean as well. I couldn't find a definitive link between reverting 165988 and running clear for this testcase, other than speculating that for this system, "cpu_present_mask" is different from "cpu_possible_mask", or that there are other changes in how IRQs are distributed that I'm not seeing exactly how. I'd feel more comfortable having another system reproducing the original issue, where we can debug/experiment better, while allowing boslcp3 to continue the test run with the current kernel (it is the closest thing we have from what will appear in GA anyway I think). ------- Comment From dnban...@us.ibm.com 2018-04-24 10:50 EDT------- When we first started looking at this bug, the captured issue seemed slightly different - a case where an skb allocation appeared to be failing due to (what appeared to be) a corrupted slab cache. Thereafter we got a series of kworker thread related failures which have been diagnosed above. However, while looking at those crashes I chanced upon an instance that seems more related to the corrputed slab cache. I decided to dig a bit to see if those instances are clearly corelated (any relation?) or if there are other things we need to be aware of. There is a crash from sometime on Friday April 20 (likely on the wrk_dbg kernel that just had the debug object cinfiguration turned on). The stack trace was a little different and it worked with the stock kernel ... KERNEL: /usr/lib/debug/boot/vmlinux-4.15.0-15-generic DUMPFILE: dump.201804201534 [PARTIAL DUMP] CPUS: 160 DATE: Fri Apr 20 15:33:10 2018 UPTIME: 00:03:51 LOAD AVERAGE: 3.22, 0.76, 0.25 TASKS: 1791 NODENAME: boslcp3 RELEASE: 4.15.0-15-generic VERSION: #16-Ubuntu SMP Wed Apr 4 13:57:51 UTC 2018 MACHINE: ppc64le (2134 Mhz) MEMORY: 128 GB PANIC: "Unable to handle kernel paging request for data at address 0x26eed6a1145b0a2a" PID: 5874 COMMAND: "systemd-udevd" TASK: c000000fe6482e00 [THREAD_INFO: c000000fe9394000] CPU: 80 STATE: TASK_RUNNING (PANIC) crash> bt PID: 5874 TASK: c000000fe6482e00 CPU: 80 COMMAND: "systemd-udevd" #0 [c000000fe93975a0] crash_kexec at c0000000001e3950 #1 [c000000fe93975e0] oops_end at c000000000025888 #2 [c000000fe9397660] bad_page_fault at c00000000006a900 #3 [c000000fe93976d0] slb_miss_bad_addr at c000000000027764 #4 [c000000fe93976f0] bad_addr_slb at c000000000008a1c Data SLB Access [380] exception frame: R0: c000000000389874 R1: c000000fe93979e0 R2: c0000000016eb400 R3: 0000000000000001 R4: 00e608fe511d18e9 R5: 00000000000003cc ^^^^^^BAD^^^^^^^^^^^^ R6: 0000000000000001 R7: 00000000000003cb R8: e608fe511d1854c2 ^^^^^^BAD^^^^^^^^^^^^ R9: 0000000000000000 R10: 0000000000000000 R11: 00000000000000f1 R12: 0000000000002000 R13: c000000007a57000 R14: c000000fdc28f080 R15: 0000000000000000 R16: 0000000000000001 R17: c000000fae88d800 R18: 0000000000000002 R19: 0000000000000000 R20: 0000000000000000 R21: 0000000000000000 R22: 0000000000000000 R23: c000000001621200 R24: e6eef6af4c054c2b R25: c000200e585e4601 R26: 26eed6a1145b0a2a ^^^^^^^BAD^^^^^^^^^^^ ^^^^^^^ptr^^^^^^^^^^^ ^^^^freelist_ptr^^^^^ R27: c000000000b32514 R28: c000000ff901ee00 R29: 00000000014000c0 ^^^^kmem_cache^^^^^^ ^^^^gfpflags^^^^^^^^^ R30: c000200e585e4601 R31: c000000ff901ee00 ^^^object^^^^^^^^^^^ NIP: c0000000003899a0 MSR: 9000000000009033 OR3: c000000000016e1c CTR: 0000000000000000 LR: c00000000038998c XER: 0000000000000000 CCR: 0000000028002808 MQ: 0000000000000001 DAR: 26eed6a1145b0a2a DSISR: 0000000000000000 Syscall Result: 0000000000000000 #5 [c000000fe93979e0] kmem_cache_alloc at c0000000003899a0 [Link Register] [c000000fe93979e0] kmem_cache_alloc at c00000000038998c (unreliable) #6 [c000000fe9397a40] skb_clone at c000000000b32514 #7 [c000000fe9397a70] netlink_broadcast_filtered at c000000000ba84a0 #8 [c000000fe9397b30] netlink_sendmsg at c000000000babae4 #9 [c000000fe9397bc0] sock_sendmsg at c000000000b1ec64 #10 [c000000fe9397bf0] ___sys_sendmsg at c000000000b20abc #11 [c000000fe9397d90] __sys_sendmsg at c000000000b221ec #12 [c000000fe9397e30] system_call at c00000000000b184 System Call [c00] exception frame: R0: 0000000000000155 R1: 00007fffe05d2e20 R2: 00007b8f72337f00 R3: 000000000000000e R4: 00007fffe05d2ec8 R5: 0000000000000000 R6: 0000000000000000 R7: 00000000000000be R8: 000000005bd10000 R9: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 00007b8f723cdaa0 R14: 00000f943ed71fd0 R15: 00000f943ed71cc0 R16: 00000f943ed71fa0 R17: 00000f942bd402c4 R18: 0000000000000003 R19: 0000000000000004 R20: 00007fffe05d3170 R21: 00007fffe05d3688 R22: 00007fffe05d3a88 R23: 0000000000000000 R24: 00000f943ed7a4b0 R25: 0000000000000000 R26: 000000005bd1e995 R27: 00000f943ed7a4b0 R28: 00000f943ed79b00 R29: 00000000000000c9 R30: 00000f943ed71cc0 R31: 0000000000000000 NIP: 00007b8f7230a940 MSR: 900000000000f033 OR3: 000000000000000e CTR: 0000000000000000 LR: 00000f942bcc4650 XER: 0000000000000000 CCR: 0000000048002402 MQ: 0000000000000001 DAR: 00000f943f026c78 DSISR: 000000000a000000 Syscall Result: 0000000000000000 Here is the relevant part of kmem_cache_alloc: 0xc0000000003896f4 <kmem_cache_alloc+0x34>: mr r29,r4 /build/linux-QzAGR9/linux-4.15.0/mm/slab.h: 414 0xc0000000003896f8 <kmem_cache_alloc+0x38>: addis r9,r2,4 0xc0000000003896fc <kmem_cache_alloc+0x3c>: addi r9,r9,-32684 /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 2737 0xc000000000389700 <kmem_cache_alloc+0x40>: mr r28,r3 <--- kmem_cache /build/linux-QzAGR9/linux-4.15.0/mm/slab.h: 414 0xc000000000389704 <kmem_cache_alloc+0x44>: lwz r31,0(r9) 0xc000000000389708 <kmem_cache_alloc+0x48>: and r31,r31,r4 /build/linux-QzAGR9/linux-4.15.0/mm/slab.h: 419 0xc00000000038970c <kmem_cache_alloc+0x4c>: andis. r9,r31,64 0xc000000000389710 <kmem_cache_alloc+0x50>: bne 0xc000000000389870 <kmem_cache_alloc+0x1b0> /build/linux-QzAGR9/linux-4.15.0/arch/powerpc/include/asm/jump_label.h: 24 0xc000000000389714 <kmem_cache_alloc+0x54>: nop /build/linux-QzAGR9/linux-4.15.0/mm/slab.h: 428 0xc000000000389718 <kmem_cache_alloc+0x58>: mr r31,r28 /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 2652 0xc00000000038971c <kmem_cache_alloc+0x5c>: cmpdi cr7,r31,0 0xc000000000389720 <kmem_cache_alloc+0x60>: beq cr7,0xc0000000003899f0 <kmem_cache_alloc+0x330> 0xc000000000389724 <kmem_cache_alloc+0x64>: std r24,32(r1) 0xc000000000389728 <kmem_cache_alloc+0x68>: std r25,40(r1) /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 2666 0xc00000000038972c <kmem_cache_alloc+0x6c>: ld r9,0(r31) 0xc000000000389730 <kmem_cache_alloc+0x70>: ld r8,48(r13) 0xc000000000389734 <kmem_cache_alloc+0x74>: addi r9,r9,8 /build/linux-QzAGR9/linux-4.15.0/include/linux/compiler.h: 183 0xc000000000389738 <kmem_cache_alloc+0x78>: ldx r5,r9,r8 /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 2667 0xc00000000038973c <kmem_cache_alloc+0x7c>: ld r10,48(r13) 0xc000000000389740 <kmem_cache_alloc+0x80>: ld r9,0(r31) 2667 c = raw_cpu_ptr(s->cpu_slab); local_paca->data_offset The data_offset: struct paca_struct { lppaca_ptr = 0xc000000007833c00, paca_index = 0x50, lock_token = 0x8000, kernel_toc = 0xc0000000016eb400, kernelbase = 0xc000000000000000, kernel_msr = 0xb000000000001033, emergency_sp = 0xc000000007be4000, data_offset = 0x200e5f6e0000, .. crash> struct kmem_cache.cpu_slab c000000ff901ee00 cpu_slab = 0xc0000000011d9d40 <mach_powernv+296> adding that to the data_offset, we get the kmem_cache_cpu crash> rd c000200e608b9d40 c000200e608b9d40: 26eed6a1145b0a2a *.[....& ^^^PROBLEM^^^^^^ PANIC: "Unable to handle kernel paging request for data at address 0x26eed6a1145b0a2a" R24: e6eef6af4c054c2b R25: c000200e585e4601 R26: 26eed6a1145b0a2a crash> rd c000200e608b9d40 16 <<<--- kmem_cache_cpu c000200e608b9d40: 26eed6a1145b0a2a 00000000000003cc *.[....&........ c000200e608b9d50: c00a000803961780 0000000000000000 ................ c000200e608b9d60: c000200e585af200 00000000000000a5 ..ZX. .......... c000200e608b9d70: c00a000803961680 0000000000000000 ................ crash> page 0xc00a000803961780 struct page { flags = 0x81ffffc00000100, { mapping = 0x0, s_mem = 0x0, compound_mapcount = { counter = 0x0 } }, { index = 0xc000200e585e9c00, freelist = 0xc000200e585e9c00 }, { counters = 0x8100007b, { { _mapcount = { counter = 0x8100007b }, active = 0x8100007b, { inuse = 0x7b, objects = 0x100, frozen = 0x1 }, units = 0x8100007b }, _refcount = { counter = 0x1 } } }, { lru = { next = 0x5deadbeef0000100, prev = 0x5deadbeef0000200 }, pgmap = 0x5deadbeef0000100, { next = 0x5deadbeef0000100, pages = 0xf0000200, pobjects = 0x5deadbee }, callback_head = { next = 0x5deadbeef0000100, func = 0x5deadbeef0000200 }, { compound_head = 0x5deadbeef0000100, compound_dtor = 0xf0000200, compound_order = 0x5deadbee } }, { private = 0xc000000ff901ee00, ptl = { { rlock = { raw_lock = { slock = 0xf901ee00 } } } }, slab_cache = 0xc000000ff901ee00 <<<--- Correct cache }, mem_cgroup = 0x0 } Back to kmem_cache_alloc: 0xc000000000389744 <kmem_cache_alloc+0x84>: add r7,r9,r10 /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 2688 0xc000000000389748 <kmem_cache_alloc+0x88>: ldx r30,r9,r10 <<<--- r30 = object 2688 object = c->freelist; /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 2689 0xc00000000038974c <kmem_cache_alloc+0x8c>: ld r9,16(r7) 2689 page = c->page; /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 2690 0xc000000000389758 <kmem_cache_alloc+0x98>: beq cr5,0xc0000000003897e0 <kmem_cache_alloc+0x120> /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 2353 0xc00000000038975c <kmem_cache_alloc+0x9c>: beq cr7,0xc0000000003897e0 <kmem_cache_alloc+0x120> /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 269 0xc000000000389760 <kmem_cache_alloc+0xa0>: lwa r9,32(r31) <<<--r9 =s->offset crash> struct kmem_cache.offset struct kmem_cache { [0x20] int offset; } /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 253 0xc000000000389764 <kmem_cache_alloc+0xa4>: ld r24,320(r31) <<<<-- r24 = s->random crash> struct kmem_cache.random struct kmem_cache { [0x140] unsigned long random; } /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 269 0xc000000000389768 <kmem_cache_alloc+0xa8>: add r25,r30,r9 return freelist_dereference(s, object + s->offset) build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 253 0xc00000000038997c <kmem_cache_alloc+0x2bc>: xor r26,r25,r24 <<<-- r26 has freelist_ptr /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 2710 0xc000000000389980 <kmem_cache_alloc+0x2c0>: std r26,0(r9) 0xc000000000389984 <kmem_cache_alloc+0x2c4>: std r5,0(r10) 0xc000000000389988 <kmem_cache_alloc+0x2c8>: bl 0xc000000000016e08 <arch_local_irq_restore+0x8> 0xc00000000038998c <kmem_cache_alloc+0x2cc>: nop /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 274 prefetch_freepointer if (object) prefetch(freelist_dereference(s, object + s->offset)); return freelist_ptr(s, (void *)*(unsigned long *)(ptr_addr), (unsigned long)ptr_addr) return (void *)((unsigned long)ptr ^ s->random ^ ptr_addr) 0xc000000000389990 <kmem_cache_alloc+0x2d0>: cmpld cr7,r25,r24 0xc000000000389994 <kmem_cache_alloc+0x2d4>: beq cr7,0xc0000000003899bc <kmem_cache_alloc+0x2fc> /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 275 0xc000000000389998 <kmem_cache_alloc+0x2d8>: lwa r9,32(r31) <<-- r9=s->offset /build/linux-QzAGR9/linux-4.15.0/mm/slub.c: 253 0xc00000000038999c <kmem_cache_alloc+0x2dc>: ld r8,320(r31) <<-- r8=s->random 0xc0000000003899a0 <kmem_cache_alloc+0x2e0>: ldx r10,r26,r9 <<<<---- CRASH!!! crash> struct kmem_cache c000000ff901ee00 struct kmem_cache { cpu_slab = 0xc0000000011d9d40 <mach_powernv+296>, flags = 0x0, min_partial = 0x5, size = 0x100, object_size = 0x100, offset = 0x0, cpu_partial = 0xd, oo = { x = 0x100 }, max = { x = 0x100 }, min = { x = 0x100 }, allocflags = 0x0, refcount = 0x11, ctor = 0x0, inuse = 0x100, align = 0x8, reserved = 0x0, red_left_pad = 0x0, name = 0xc000000000f90a10 "kmalloc-256", list = { next = 0xc000000ff901f068, prev = 0xc000000ff901ec68 }, kobj = { name = 0xc000000ff0a00120 ":0000256", entry = { next = 0xc000000ff901f080, prev = 0xc000000ff901ec80 }, parent = 0xc000000ff0a107f8, kset = 0xc000000ff0a107e0, ktype = 0xc0000000015b6500 <slab_ktype>, sd = 0xc000000fe1cdde10, kref = { refcount = { refs = { counter = 0x2 } } }, ... } What happened here is the following: netlink_sendmsg -> skb_clone -> kmem_cache_alloc, using the kmalloc-256 cache: R28: c000000ff901ee00 The relevant data ================== R24: e6eef6af4c054c2b R25: c000200e585e4601 R26: 26eed6a1145b0a2a ^^^^^^^BAD^^^^^^^^^^^ ^^^^^^^ptr^^^^^^^^^^^ ^^^^freelist_ptr^^^^^ R27: c000000000b32514 R28: c000000ff901ee00 R29: 00000000014000c0 ^^^^kmem_cache^^^^^^ R30: c000200e585e4601 R31: c000000ff901ee00 ^^^object^^^^^^^^^^^ The relevant code (at crash time) - just including skeleton code ================================ c = raw_cpu_ptr(s->cpu_slab); ... object = c->freelist; page = c->page; ... void *next_object = get_freepointer_safe(s, object); ... this_cpu_cmpxchg_double( s->cpu_slab->freelist, s->cpu_slab->tid, object, tid, next_object, next_tid(tid)))) { ... prefetch_freepointer(s, next_object); Basically, the netlink code is cloning an skb which requests a skb header from 256 byte kmalloc cache (c000000ff901ee00). There we get the kmem_cache_cpu (for this cpu 0x50) - s->cpu_slab. We retrieve the freelist pointer into object and the page. object = c000200e585e4601 Thereafter, we refernce the current object/freepointer to get the next object (next_object). Prefetching this leads to a problem! Current freelist_ptr is 26eed6a1145b0a2a which we try to dereference and crash. PANIC: "Unable to handle kernel paging request for data at address 0x26eed6a1145b0a2a" It is to be noted that the object = c000200e585e4601 looks strange. Almost feels like someone incremented that location (while it is on the freelist? or could it be freed that way?). The issue is that the freelist got corrupted and we crash trying to access it. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1762844 Title: ISST-LTE:KVM:Ubuntu1804:BostonLC:boslcp3: Host crashed & enters into xmon after moving to 4.15.0-15.16 kernel Status in The Ubuntu-power-systems project: Incomplete Status in linux package in Ubuntu: Incomplete Status in linux source package in Bionic: Incomplete Bug description: Problem Description: =================== Host crashed & enters into xmon after updating to 4.15.0-15.16 kernel kernel. Steps to re-create: ================== 1. boslcp3 is up with BMC:118 & PNOR: 20180330 levels 2. Installed boslcp3 with latest kernel 4.15.0-13-generic 3. Enabled "-proposed" kernel in /etc/apt/sources.list file 4. Ran sudo apt-get update & apt-get upgrade 5. root@boslcp3:~# ls /boot abi-4.15.0-13-generic retpoline-4.15.0-13-generic abi-4.15.0-15-generic retpoline-4.15.0-15-generic config-4.15.0-13-generic System.map-4.15.0-13-generic config-4.15.0-15-generic System.map-4.15.0-15-generic grub vmlinux initrd.img vmlinux-4.15.0-13-generic initrd.img-4.15.0-13-generic vmlinux-4.15.0-15-generic initrd.img-4.15.0-15-generic vmlinux.old initrd.img.old 6. Rebooted & booted with 4.15.0-15 kernel 7. Enabled xmon by editing file "vi /etc/default/grub" and ran update-grub 8. Rebooted host. 9. Booted with 4.15.0-15 & provided root/password credentials in login prompt 10. Host crashed & enters into XMON state with 'Unable to handle kernel paging request' root@boslcp3:~# [ 66.295233] Unable to handle kernel paging request for data at address 0x8882f6ed90e9151a [ 66.295297] Faulting instruction address: 0xc00000000038a110 cpu 0x50: Vector: 380 (Data Access Out of Range) at [c00000000692f650] pc: c00000000038a110: kmem_cache_alloc_node+0x2f0/0x350 lr: c00000000038a0fc: kmem_cache_alloc_node+0x2dc/0x350 sp: c00000000692f8d0 msr: 9000000000009033 dar: 8882f6ed90e9151a current = 0xc00000000698fd00 paca = 0xc00000000fab7000 softe: 0 irq_happened: 0x01 pid = 1762, comm = systemd-journal Linux version 4.15.0-15-generic (buildd@bos02-ppc64el-002) (gcc version 7.3.0 (Ubuntu 7.3.0-14ubuntu1)) #16-Ubuntu SMP Wed Apr 4 13:57:51 UTC 2018 (Ubuntu 4.15.0-15.16-generic 4.15.15) enter ? for help [c00000000692f8d0] c000000000389fd4 kmem_cache_alloc_node+0x1b4/0x350 (unreliable) [c00000000692f940] c000000000b2ec6c __alloc_skb+0x6c/0x220 [c00000000692f9a0] c000000000b30b6c alloc_skb_with_frags+0x7c/0x2e0 [c00000000692fa30] c000000000b247cc sock_alloc_send_pskb+0x29c/0x2c0 [c00000000692fae0] c000000000c5705c unix_dgram_sendmsg+0x15c/0x8f0 [c00000000692fbc0] c000000000b1ec64 sock_sendmsg+0x64/0x90 [c00000000692fbf0] c000000000b20abc ___sys_sendmsg+0x31c/0x390 [c00000000692fd90] c000000000b221ec __sys_sendmsg+0x5c/0xc0 [c00000000692fe30] c00000000000b184 system_call+0x58/0x6c --- Exception: c00 (System Call) at 000074826f6fa9c4 SP (7ffff5dc5510) is in userspace 50:mon> 50:mon> 10. Attached Host console logs I rebooted the host just to see if it would hit the issue again and this time I didn't even get to the login prompt but it crashed in the same location: 50:mon> r R00 = c000000000389fd4 R16 = c000200e0b20fdc0 R01 = c000200e0b20f8d0 R17 = 0000000000000048 R02 = c0000000016eb400 R18 = 000000000001fe80 R03 = 0000000000000001 R19 = 0000000000000000 R04 = 0048ca1cff37803d R20 = 0000000000000000 R05 = 0000000000000688 R21 = 0000000000000000 R06 = 0000000000000001 R22 = 0000000000000048 R07 = 0000000000000687 R23 = 4882d6e3c8b7ab55 R08 = 48ca1cff37802b68 R24 = c000200e5851df01 R09 = 0000000000000000 R25 = 8882f6ed90e67454 R10 = 0000000000000000 R26 = c000000000b2ec6c R11 = c000000000d10f78 R27 = c000000ff901ee00 R12 = 0000000000002000 R28 = ffffffffffffffff R13 = c00000000fab7000 R29 = 00000000015004c0 R14 = c000200e4c973fc8 R30 = c000200e5851df01 R15 = c000200e4c974238 R31 = c000000ff901ee00 pc = c00000000038a110 kmem_cache_alloc_node+0x2f0/0x350 cfar= c000000000016e1c arch_local_irq_restore+0x1c/0x90 lr = c00000000038a0fc kmem_cache_alloc_node+0x2dc/0x350 msr = 9000000000009033 cr = 28002844 ctr = c00000000061e1b0 xer = 0000000000000000 trap = 380 dar = 8882f6ed90e67454 dsisr = c000200e40bd8400 50:mon> t [c000200e0b20f8d0] c000000000389fd4 kmem_cache_alloc_node+0x1b4/0x350 (unreliable) [c000200e0b20f940] c000000000b2ec6c __alloc_skb+0x6c/0x220 [c000200e0b20f9a0] c000000000b30b6c alloc_skb_with_frags+0x7c/0x2e0 [c000200e0b20fa30] c000000000b247cc sock_alloc_send_pskb+0x29c/0x2c0 [c000200e0b20fae0] c000000000c56ae4 unix_stream_sendmsg+0x264/0x5c0 [c000200e0b20fbc0] c000000000b1ec64 sock_sendmsg+0x64/0x90 [c000200e0b20fbf0] c000000000b20abc ___sys_sendmsg+0x31c/0x390 [c000200e0b20fd90] c000000000b221ec __sys_sendmsg+0x5c/0xc0 [c000200e0b20fe30] c00000000000b184 system_call+0x58/0x6c --- Exception: c01 (System Call) at 00007d16a993a940 SP (7ffffbee2270) is in userspace Mirroring to Canonical to advise them that this might be possible regression. Didn't see any obvious changes in this area in the changelog published at https://launchpad.net/ubuntu/+source/linux/4.15.0-15.16 but it would be good to have Canonical help reviewing the deltas as we try to isolate this further. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-power-systems/+bug/1762844/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp