[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v2] xen: credit1: fix tickling when it happens from a remote pCPU
especially if that is also from a different cpupool than the processor of the vCPU that triggered the tickling. In fact, it is possible that we get as far as calling vcpu_unblock()--> vcpu_wake()-->csched_vcpu_wake()-->__runq_tickle() for the vCPU 'vc', but all while running on a pCPU that is different from 'vc->processor'. For instance, this can happen when an HVM domain runs in a cpupool, with a different scheduler than the default one, and issues IOREQs to Dom0, running in Pool-0 with the default scheduler. In fact, right in this case, the following crash can be observed: (XEN) ----[ Xen-4.7-unstable x86_64 debug=y Tainted: C ]---- (XEN) CPU: 7 (XEN) RIP: e008:[<ffff82d0801230de>] __runq_tickle+0x18f/0x430 (XEN) RFLAGS: 0000000000010086 CONTEXT: hypervisor (d1v0) (XEN) rax: 0000000000000001 rbx: ffff8303184fee00 rcx: 0000000000000000 (XEN) ... ... ... (XEN) Xen stack trace from rsp=ffff83031fa57a08: (XEN) ffff82d0801fe664 ffff82d08033c820 0000000100000002 0000000a00000001 (XEN) 0000000000006831 0000000000000000 0000000000000000 0000000000000000 (XEN) ... ... ... (XEN) Xen call trace: (XEN) [<ffff82d0801230de>] __runq_tickle+0x18f/0x430 (XEN) [<ffff82d08012348a>] csched_vcpu_wake+0x10b/0x110 (XEN) [<ffff82d08012b421>] vcpu_wake+0x20a/0x3ce (XEN) [<ffff82d08012b91c>] vcpu_unblock+0x4b/0x4e (XEN) [<ffff82d080167bd0>] vcpu_kick+0x17/0x61 (XEN) [<ffff82d080167c46>] vcpu_mark_events_pending+0x2c/0x2f (XEN) [<ffff82d08010ac35>] evtchn_fifo_set_pending+0x381/0x3f6 (XEN) [<ffff82d08010a0f6>] notify_via_xen_event_channel+0xc9/0xd6 (XEN) [<ffff82d0801c29ed>] hvm_send_ioreq+0x3e9/0x441 (XEN) [<ffff82d0801bba7d>] hvmemul_do_io+0x23f/0x2d2 (XEN) [<ffff82d0801bbb43>] hvmemul_do_io_buffer+0x33/0x64 (XEN) [<ffff82d0801bc92b>] hvmemul_do_pio_buffer+0x35/0x37 (XEN) [<ffff82d0801cc49f>] handle_pio+0x58/0x14c (XEN) [<ffff82d0801eabcb>] vmx_vmexit_handler+0x16b3/0x1bea (XEN) [<ffff82d0801efd21>] vmx_asm_vmexit_handler+0x41/0xc0 In this case, pCPU 7 is not in Pool-0, while the (Dom0's) vCPU being woken is. pCPU's 7 pool has a different scheduler than credit, but it is, however, right from pCPU 7 that we are waking the Dom0's vCPUs. Therefore, the current code tries to access csched_balance_mask for pCPU 7, but that is not defined, and hence the Oops. (Note that, in case the two pools run the same scheduler we see no Oops, but things are still conceptually wrong.) Cure things by making the csched_balance_mask macro accept a parameter for fetching a specific pCPU's mask (instead than always using smp_processor_id()). Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx> Reviewed-by: Juergen Gross <jgross@xxxxxxxx> --- Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx> Cc: Jan Beulich <jbeulich@xxxxxxxx> --- Changes from v1: * get rid of the old macro and always use the new one, as suggested during review (Juergen) --- xen/common/sched_credit.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c index a1945ac..57967c1 100644 --- a/xen/common/sched_credit.c +++ b/xen/common/sched_credit.c @@ -171,10 +171,10 @@ struct csched_pcpu { * Convenience macro for accessing the per-PCPU cpumask we need for * implementing the two steps (soft and hard affinity) balancing logic. * It is stored in csched_pcpu so that serialization is not an issue, - * as there is a csched_pcpu for each PCPU and we always hold the - * runqueue spin-lock when using this. + * as there is a csched_pcpu for each PCPU, and we always hold the + * runqueue lock for the proper PCPU when using this. */ -#define csched_balance_mask (CSCHED_PCPU(smp_processor_id())->balance_mask) +#define csched_balance_mask(c) (CSCHED_PCPU(c)->balance_mask) /* * Virtual CPU @@ -412,9 +412,10 @@ __runq_tickle(unsigned int cpu, struct csched_vcpu *new) /* Are there idlers suitable for new (for this balance step)? */ csched_balance_cpumask(new->vcpu, balance_step, - csched_balance_mask); - cpumask_and(csched_balance_mask, csched_balance_mask, &idle_mask); - new_idlers_empty = cpumask_empty(csched_balance_mask); + csched_balance_mask(cpu)); + cpumask_and(csched_balance_mask(cpu), + csched_balance_mask(cpu), &idle_mask); + new_idlers_empty = cpumask_empty(csched_balance_mask(cpu)); /* * Let's not be too harsh! If there aren't idlers suitable @@ -1491,8 +1492,9 @@ csched_runq_steal(int peer_cpu, int cpu, int pri, int balance_step) && !__vcpu_has_soft_affinity(vc, vc->cpu_hard_affinity) ) continue; - csched_balance_cpumask(vc, balance_step, csched_balance_mask); - if ( __csched_vcpu_is_migrateable(vc, cpu, csched_balance_mask) ) + csched_balance_cpumask(vc, balance_step, csched_balance_mask(cpu)); + if ( __csched_vcpu_is_migrateable(vc, cpu, + csched_balance_mask(cpu)) ) { /* We got a candidate. Grab it! */ TRACE_3D(TRC_CSCHED_STOLEN_VCPU, peer_cpu, _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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