Xen project Mailing List

Re: CPU_DOWN_FAILED hits ASSERTs in scheduling logic

From: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Date: Wed, 29 May 2024 18:03:06 +0200

Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Dario Faggioli <dfaggioli@xxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>

Delivery-date: Wed, 29 May 2024 16:03:19 +0000

List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On Wed, May 29, 2024 at 03:08:49PM +0200, Jürgen Groß wrote: > On 29.05.24 14:46, Roger Pau Monné wrote: > > On Wed, May 29, 2024 at 01:47:09PM +0200, Jürgen Groß wrote: > > > On 28.05.24 13:22, Roger Pau Monné wrote: > > > > Hello, > > > > > > > > When the stop_machine_run() call in cpu_down() fails and calls the CPU > > > > notifier CPU_DOWN_FAILED hook the following assert triggers in the > > > > scheduling code: > > > > > > > > Assertion '!cpumask_test_cpu(cpu, &prv->initialized)' failed at > > > > common/sched/cred1 > > > > ----[ Xen-4.19-unstable x86_64 debug=y Tainted: C ]---- > > > > CPU: 0 > > > > RIP: e008:[<ffff82d040248299>] > > > > common/sched/credit2.c#csched2_free_pdata+0xc8/0x177 > > > > RFLAGS: 0000000000010093 CONTEXT: hypervisor > > > > rax: 0000000000000000 rbx: ffff83202ecc2f80 rcx: ffff83202f3e64c0 > > > > rdx: 0000000000000001 rsi: 0000000000000002 rdi: ffff83202ecc2f88 > > > > rbp: ffff83203ffffd58 rsp: ffff83203ffffd30 r8: 0000000000000000 > > > > r9: ffff83202f3e6e01 r10: 0000000000000000 r11: 0f0f0f0f0f0f0f0f > > > > r12: ffff83202ecb80b0 r13: 0000000000000001 r14: 0000000000000282 > > > > r15: ffff83202ecbbf00 cr0: 000000008005003b cr4: 00000000007526e0 > > > > cr3: 00000000574c2000 cr2: 0000000000000000 > > > > fsb: 0000000000000000 gsb: 0000000000000000 gss: 0000000000000000 > > > > ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: 0000 cs: e008 > > > > Xen code around <ffff82d040248299> > > > > (common/sched/credit2.c#csched2_free_pdata+0xc8/0x177): > > > > fe ff eb 9a 0f 0b 0f 0b <0f> 0b 49 8d 4f 08 49 8b 47 08 48 3b 48 08 > > > > 75 2e > > > > Xen stack trace from rsp=ffff83203ffffd30: > > > > ffff83202d74d100 0000000000000001 ffff82d0404c4430 0000000000000006 > > > > 0000000000000000 ffff83203ffffd78 ffff82d040257454 0000000000000000 > > > > 0000000000000001 ffff83203ffffda8 ffff82d04021f303 ffff82d0404c4628 > > > > ffff82d0404c4620 ffff82d0404c4430 0000000000000006 ffff83203ffffdf0 > > > > ffff82d04022bc4c ffff83203ffffe18 0000000000000001 0000000000000001 > > > > 00000000fffffff0 0000000000000000 0000000000000000 ffff82d0405e6500 > > > > ffff83203ffffe08 ffff82d040204fd5 0000000000000001 ffff83203ffffe30 > > > > ffff82d0402054f0 ffff82d0404c5860 0000000000000001 ffff83202ec75000 > > > > ffff83203ffffe48 ffff82d040348c25 ffff83202d74d0d0 ffff83203ffffe68 > > > > ffff82d0402071aa ffff83202ec751d0 ffff82d0405ce210 ffff83203ffffe80 > > > > ffff82d0402343c9 ffff82d0405ce200 ffff83203ffffeb0 ffff82d040234631 > > > > 0000000000000000 0000000000007fff ffff82d0405d5080 ffff82d0405ce210 > > > > ffff83203ffffee8 ffff82d040321411 ffff82d040321399 ffff83202f3a9000 > > > > 0000000000000000 0000001d91a6fa2d ffff82d0405e6500 ffff83203ffffde0 > > > > ffff82d040324391 0000000000000000 0000000000000000 0000000000000000 > > > > 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > > > > 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > > > > 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > > > > 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > > > > 0000000000000000 0000000000000000 0000000000000000 0000000000000000 > > > > Xen call trace: > > > > [<ffff82d040248299>] R > > > > common/sched/credit2.c#csched2_free_pdata+0xc8/0x177 > > > > [<ffff82d040257454>] F free_cpu_rm_data+0x41/0x58 > > > > [<ffff82d04021f303>] F > > > > common/sched/cpupool.c#cpu_callback+0xfb/0x466 > > > > [<ffff82d04022bc4c>] F notifier_call_chain+0x6c/0x96 > > > > [<ffff82d040204fd5>] F > > > > common/cpu.c#cpu_notifier_call_chain+0x1b/0x36 > > > > [<ffff82d0402054f0>] F cpu_down+0xa7/0x143 > > > > [<ffff82d040348c25>] F cpu_down_helper+0x11/0x27 > > > > [<ffff82d0402071aa>] F > > > > common/domain.c#continue_hypercall_tasklet_handler+0x50/0xbd > > > > [<ffff82d0402343c9>] F common/tasklet.c#do_tasklet_work+0x76/0xaf > > > > [<ffff82d040234631>] F do_tasklet+0x5b/0x8d > > > > [<ffff82d040321411>] F arch/x86/domain.c#idle_loop+0x78/0xe6 > > > > [<ffff82d040324391>] F continue_running+0x5b/0x5d > > > > > > > > > > > > **************************************** > > > > Panic on CPU 0: > > > > Assertion '!cpumask_test_cpu(cpu, &prv->initialized)' failed at > > > > common/sched/credit2.c:4111 > > > > **************************************** > > > > > > > > The issue seems to be that since the CPU hasn't been removed, it's > > > > still part of prv->initialized and the assert in csched2_free_pdata() > > > > called as part of free_cpu_rm_data() triggers. > > > > > > > > It's easy to reproduce by substituting the stop_machine_run() call in > > > > cpu_down() with an error. > > > > > > Could you please give the attached patch a try? > > > > I still get the following assert: > > Oh, silly me. Without core scheduling active nr_sr_unused will be 0 all > the time. :-( > > Next try. I'm afraid I have a new trace for you: Assertion '!cpumask_test_cpu(cpu, &prv->initialized)' failed at common/sched/credit2.c:3987 ----[ Xen-4.19-unstable x86_64 debug=y Not tainted ]---- CPU: 0 RIP: e008:[<ffff82d040247d27>] common/sched/credit2.c#csched2_switch_sched+0x115/0x339 RFLAGS: 0000000000010093 CONTEXT: hypervisor rax: 000000000000c000 rbx: 0000000000000001 rcx: ffff82d0405e6500 rdx: 0000004feee13000 rsi: 0000000000000004 rdi: ffff83202ecc2f88 rbp: ffff83203ffffc80 rsp: ffff83203ffffc38 r8: 0000000000000000 r9: ffff83202ecbbf01 r10: 0000000000000000 r11: 0f0f0f0f0f0f0f0f r12: ffff83202ecc2f80 r13: ffff83402ca50100 r14: ffff83402ca50140 r15: ffff83202ecc2f88 cr0: 000000008005003b cr4: 00000000007526e0 cr3: 00000000574c2000 cr2: 0000000000000000 fsb: 0000000000000000 gsb: 0000000000000000 gss: 0000000000000000 ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: 0000 cs: e008 Xen code around <ffff82d040247d27> (common/sched/credit2.c#csched2_switch_sched+0x115/0x339): 7c ff ff ff 0f 0b 0f 0b <0f> 0b 0f 0b 41 8b 56 30 89 de 48 8d 3d e8 00 1a Xen stack trace from rsp=ffff83203ffffc38: ffff83203ffffc48 ffff82d0402332ba ffff83203ffffc68 ffff82d04023343d 0000000000000001 ffff82d0405cf398 ffff83402ca50100 ffff82d0405e6500 ffff83202ecbbdb0 ffff83203ffffd18 ffff82d040256e1a ffff83203fff386c ffff83203fff2000 0000000000000005 ffff83202ecbbf00 ffff83402ca50140 ffff83203fff3868 0000000000000282 0000000040233509 ffff83202ecbbdb0 ffff83402ca50100 ffff83202f3e6d80 ffff83202ecc2ec0 ffff83202ecc2ec0 0000000000000001 ffff82d0403da460 0000000000000048 0000000000000000 ffff83203ffffd48 ffff82d0402414b7 0000000000000001 0000000000000000 ffff82d0403da460 0000000000000006 ffff83203ffffd70 ffff82d04024173d 0000000000000000 0000000000000001 ffff82d0404c4430 ffff83203ffffda0 ffff82d04021f1f9 ffff82d0404c4628 ffff82d0404c4620 ffff82d0404c4430 0000000000000006 ffff83203ffffde8 ffff82d04022bb2f ffff83203ffffe10 0000000000000001 0000000000000001 0000000000000000 ffff83203ffffe10 0000000000000000 ffff82d0405e6500 ffff83203ffffe00 ffff82d040204fd5 0000000000000001 ffff83203ffffe30 ffff82d040205464 ffff82d0404c5860 0000000000000001 ffff83202ec86000 0000000000000000 ffff83203ffffe48 ffff82d040348c32 ffff83402ca500d0 ffff83203ffffe68 ffff82d04020708d ffff83202ec861d0 ffff82d0405ce210 ffff83203ffffe80 ffff82d0402342a3 ffff82d0405ce200 ffff83203ffffeb0 ffff82d04023450b 0000000000000000 0000000000007fff ffff82d0405d5080 ffff82d0405ce210 ffff83203ffffee8 Xen call trace: [<ffff82d040247d27>] R common/sched/credit2.c#csched2_switch_sched+0x115/0x339 [<ffff82d040256e1a>] F schedule_cpu_add+0x1a4/0x463 [<ffff82d0402414b7>] F common/sched/cpupool.c#cpupool_assign_cpu_locked+0x5a/0x17e [<ffff82d04024173d>] F common/sched/cpupool.c#cpupool_cpu_add+0x162/0x16c [<ffff82d04021f1f9>] F common/sched/cpupool.c#cpu_callback+0x10e/0x466 [<ffff82d04022bb2f>] F notifier_call_chain+0x6c/0x96 [<ffff82d040204fd5>] F common/cpu.c#cpu_notifier_call_chain+0x1b/0x36 [<ffff82d040205464>] F cpu_down+0x60/0x83 [<ffff82d040348c32>] F cpu_down_helper+0x11/0x27 [<ffff82d04020708d>] F common/domain.c#continue_hypercall_tasklet_handler+0x50/0xbd [<ffff82d0402342a3>] F common/tasklet.c#do_tasklet_work+0x76/0xaf [<ffff82d04023450b>] F do_tasklet+0x5b/0x8d [<ffff82d040321372>] F arch/x86/domain.c#idle_loop+0x78/0xe6 [<ffff82d0403242f2>] F continue_running+0x5b/0x5d **************************************** Panic on CPU 0: Assertion '!cpumask_test_cpu(cpu, &prv->initialized)' failed at common/sched/credit2.c:3987 **************************************** This time is one of the asserts in init_pdata(). Roger.

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