On 04.04.25 09:24, Jan Beulich wrote:
On 03.04.2025 23:48, Stewart Hildebrand wrote:The following sequence of events may lead a debug build of Xen to crash when using the null scheduler:1. domain creation (e.g. d1) failed due to bad configuration 2. complete_domain_destroy() was deferred 3. domain creation (e.g. d2) succeeds At this point, d2 is running, while the zombie d1 is not fully cleaned up: (XEN) Online Cpus: 0-3 (XEN) Cpupool 0: (XEN) Cpus: 0-3 (XEN) Scheduling granularity: cpu, 1 CPU per sched-resource (XEN) Scheduler: null Scheduler (null) (XEN) cpus_free = 3 (XEN) Domain info: (XEN) Domain: 0 (XEN) 1: [0.0] pcpu=0 (XEN) 2: [0.1] pcpu=1 (XEN) Domain: 1 (XEN) 3: [1.0] pcpu=2 (XEN) Domain: 2 (XEN) 4: [2.0] pcpu=2 4. complete_domain_destroy() gets called for d1 and triggers the following: (XEN) Xen call trace: (XEN) [<00000a0000322ed4>] null.c#unit_deassign+0x2d8/0xb70 (PC) (XEN) [<00000a000032457c>] null.c#null_unit_remove+0x670/0xba8 (LR) (XEN) [<00000a000032457c>] null.c#null_unit_remove+0x670/0xba8 (XEN) [<00000a0000336404>] sched_destroy_vcpu+0x354/0x8fc (XEN) [<00000a0000227324>] domain.c#complete_domain_destroy+0x11c/0x49c (XEN) [<00000a000029fbd0>] rcupdate.c#rcu_do_batch+0x94/0x3d0 (XEN) [<00000a00002a10c0>] rcupdate.c#__rcu_process_callbacks+0x160/0x5f4 (XEN) [<00000a00002a1e60>] rcupdate.c#rcu_process_callbacks+0xcc/0x1b0 (XEN) [<00000a00002a3460>] softirq.c#__do_softirq+0x1f4/0x3d8 (XEN) [<00000a00002a37c4>] do_softirq+0x14/0x1c (XEN) [<00000a0000465260>] traps.c#check_for_pcpu_work+0x30/0xb8 (XEN) [<00000a000046bb08>] leave_hypervisor_to_guest+0x28/0x198 (XEN) [<00000a0000409c84>] entry.o#guest_sync_slowpath+0xac/0xd8 (XEN) (XEN) **************************************** (XEN) Panic on CPU 0: (XEN) Assertion 'npc->unit == unit' failed at common/sched/null.c:383 (XEN) **************************************** Fix by skipping unit_deassign() when the unit to be removed does not match the pcpu's currently assigned unit. Signed-off-by: Stewart Hildebrand <stewart.hildebr...@amd.com>Just one remark here: This almost certainly wants a Fixes: tag.
This will probably be d671da3be3ca (the initial NULL scheduler commit). Juergen
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