[Xen-changelog] [xen stable-4.4] credit1: fix tickling when it happens from a remote pCPU

[patchbot@xxxxxxx]

commit 59670732ca1a90977b8a3636e1bd2ef23486e57e
Author:     Dario Faggioli <dario.faggioli@xxxxxxxxxx>
AuthorDate: Thu Oct 8 12:46:06 2015 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Oct 8 12:46:06 2015 +0200

    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>
    Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>
    master commit: ea5637968a09a81a64fa5fd73ce49b4ea9789e12
    master date: 2015-09-30 14:44:22 +0200
---
 xen/common/sched_credit.c |   18 ++++++++++--------
 1 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index 1d38adb..81f3510 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -140,10 +140,10 @@ struct csched_pcpu {
  * Convenience macro for accessing the per-PCPU cpumask we need for
  * implementing the two steps (vcpu and node 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
@@ -417,9 +417,10 @@ __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
@@ -1506,8 +1507,9 @@ csched_runq_steal(int peer_cpu, int cpu, int pri, int 
balance_step)
                  && !__vcpu_has_node_affinity(vc, vc->cpu_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,
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.4

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