[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] xen/arm: Assertion 'timer->status >= TIMER_STATUS_inactive' failed at timer.c:279

Hi Dario and George,

What is the status of this patch? It would be nice to have it for Xen 4.7 to avoid unwanted crash when secondary CPUs fails to come online.


On 26/04/16 18:49, Dario Faggioli wrote:
On Tue, 2016-04-26 at 15:25 +0100, Julien Grall wrote:
Hi Dario,


A couple of people have been reported Xen crash on the ARM64
Foundation Model [1] with recent unstable.

Ok, thanks for reporting.

The crash seems to happen when Xen fails to bring up secondary CPUs
(see stack trace below).

Ah... I see.

 From my understanding, csched_free_pdata is trying to kill the
timer spc->ticker. However the status of this timer is

This is because csched_init_pdata has set a deadline for the
timer (set_timer) and the softirq to schedule the timer has
not yet happen (indeed Xen is still in early boot).

Yes, this is sort of what happens (only slightly different, see the
changelog of the atached patch patch).

I am not sure how to fix this issue. How will you recommend
to fix it?

Yeah, well, doing it cleanly includes a slight change in the scheduler
hooks API, IMO... and we indeed should do it cleanly :-))

George, what do you think?

Honestly, this is similar to what I was thinking to do already (I mean,
having an deinit_pdata hook, "symmetric" with the init_pdata one), when
working on that series, because I do think it's cleaner... then, I
abandoned the idea, as it looked to not be necessary... But apparently
it may actually be! :-)

Let me know, and I'll resubmit the patch properly (together with
another bugfix I have in my queue).

commit eca4d65fb67a71c0f6563aafbfdd68e566c53c32
Author: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Date:   Tue Apr 26 17:42:36 2016 +0200

     xen: sched: fix killing an uninitialized timer in free_pdata.

     commit 64269d9365 "sched: implement .init_pdata in Credit,
     Credit2 and RTDS" helped fixing Credit2 runqueues, and
     the races we had in switching scheduler for pCPUs, but
     introduced another issue. In fact, if CPU bringup fails
     during __cpu_up() (and, more precisely, after CPU_UP_PREPARE,
     but before CPU_STARTING) the CPU_UP_CANCELED notifier
     would be executed, which calls the free_pdata hook.

     Such hook does two things: (1) undo the initialization
     done inside the init_pdata hook; (2) free the memory
     allocated by the alloc_pdata hook.

     However, in the failure path just described, it is possible
     that only alloc_pdata has really been called, which is
     potentially and issue (depending on what actually happens
     inside the implementation of free_pdata).

     In fact, for Credit1 (the only scheduler that actually
     allocates per-pCPU data), this result in calling kill_timer()
     on a timer that had not yet been initialized, which causes
     the following:

     (XEN) Xen call trace:
     (XEN)    [<000000000022e304>] timer.c#active_timer+0x8/0x24 (PC)
     (XEN)    [<000000000022f624>] kill_timer+0x108/0x2e0 (LR)
     (XEN)    [<00000000002208c0>] sched_credit.c#csched_free_pdata+0xd8/0x114
     (XEN)    [<0000000000227a18>] schedule.c#cpu_schedule_callback+0xc0/0x12c
     (XEN)    [<0000000000219944>] notifier_call_chain+0x78/0x9c
     (XEN)    [<00000000002015fc>] cpu_up+0x104/0x130
     (XEN)    [<000000000028f7c0>] start_xen+0xaf8/0xce0
     (XEN)    [<00000000810021d8>] 00000000810021d8
     (XEN) ****************************************
     (XEN) Panic on CPU 0:
     (XEN) Assertion 'timer->status >= TIMER_STATUS_inactive' failed at 
     (XEN) ****************************************

     Solve this by making the scheduler hooks API symmetric again,
     i.e., by adding an deinit_pdata hook and making it responsible
     of undoing what init_pdata did, rather than asking to free_pdata
     to do everything.

     This is cleaner and, in the case at hand, makes it possible to
     only call free_pdata, which is the right thing to do, as only
     allocation and no initialization was performed.

     Reported-by: Julien Grall <julien.grall@xxxxxxx>
     Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
     Cc: George Dunlap <george.dunlap@xxxxxxxxxx>
     Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
     Cc: Varun.Swara@xxxxxxx
     Cc: Steve Capper <Steve.Capper@xxxxxxx>

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index bc36837..0a6a1b4 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -482,15 +482,25 @@ static inline void __runq_tickle(struct csched_vcpu *new)

  static void
-csched_free_pdata(const struct scheduler *ops, void *pcpu, int cpu)
+csched_free_pdata(const struct scheduler *ops, void *pcpu)
-    struct csched_private *prv = CSCHED_PRIV(ops);
      struct csched_pcpu *spc = pcpu;
-    unsigned long flags;

      if ( spc == NULL )

+    xfree(spc);
+static void
+csched_deinit_pdata(const struct scheduler *ops, void *pcpu, int cpu)
+    struct csched_private *prv = CSCHED_PRIV(ops);
+    struct csched_pcpu *spc = pcpu;
+    unsigned long flags;
+    ASSERT(spc != NULL);
      spin_lock_irqsave(&prv->lock, flags);

      prv->credit -= prv->credits_per_tslice;
@@ -507,8 +517,6 @@ csched_free_pdata(const struct scheduler *ops, void *pcpu, 
int cpu)

      spin_unlock_irqrestore(&prv->lock, flags);
-    xfree(spc);

  static void *
@@ -2091,6 +2099,7 @@ static const struct scheduler sched_credit_def = {
      .free_vdata     = csched_free_vdata,
      .alloc_pdata    = csched_alloc_pdata,
      .init_pdata     = csched_init_pdata,
+    .deinit_pdata   = csched_deinit_pdata,
      .free_pdata     = csched_free_pdata,
      .switch_sched   = csched_switch_sched,
      .alloc_domdata  = csched_alloc_domdata,
diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 46b9279..f4c37b4 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -2261,13 +2261,15 @@ csched2_switch_sched(struct scheduler *new_ops, 
unsigned int cpu,

  static void
-csched2_free_pdata(const struct scheduler *ops, void *pcpu, int cpu)
+csched2_deinit_pdata(const struct scheduler *ops, void *pcpu, int cpu)
      unsigned long flags;
      struct csched2_private *prv = CSCHED2_PRIV(ops);
      struct csched2_runqueue_data *rqd;
      int rqi;

+    ASSERT(pcpu == NULL);
      spin_lock_irqsave(&prv->lock, flags);

      ASSERT(cpumask_test_cpu(cpu, &prv->initialized));
@@ -2387,7 +2389,7 @@ static const struct scheduler sched_credit2_def = {
      .alloc_vdata    = csched2_alloc_vdata,
      .free_vdata     = csched2_free_vdata,
      .init_pdata     = csched2_init_pdata,
-    .free_pdata     = csched2_free_pdata,
+    .deinit_pdata   = csched2_deinit_pdata,
      .switch_sched   = csched2_switch_sched,
      .alloc_domdata  = csched2_alloc_domdata,
      .free_domdata   = csched2_free_domdata,
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 5546999..1a64521 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -1529,7 +1529,7 @@ static void cpu_schedule_down(unsigned int cpu)
      struct schedule_data *sd = &per_cpu(schedule_data, cpu);
      struct scheduler *sched = per_cpu(scheduler, cpu);

-    SCHED_OP(sched, free_pdata, sd->sched_priv, cpu);
+    SCHED_OP(sched, free_pdata, sd->sched_priv);
      SCHED_OP(sched, free_vdata, idle_vcpu[cpu]->sched_priv);

      idle_vcpu[cpu]->sched_priv = NULL;
@@ -1554,8 +1554,10 @@ static int cpu_schedule_callback(
      case CPU_UP_PREPARE:
          rc = cpu_schedule_up(cpu);
-    case CPU_UP_CANCELED:
      case CPU_DEAD:
+        SCHED_OP(sched, deinit_pdata, sd->sched_priv, cpu);
+        /* Fallthrough */
+    case CPU_UP_CANCELED:
@@ -1684,7 +1686,7 @@ int schedule_cpu_switch(unsigned int cpu, struct cpupool 
      vpriv = SCHED_OP(new_ops, alloc_vdata, idle, idle->domain->sched_priv);
      if ( vpriv == NULL )
-        SCHED_OP(new_ops, free_pdata, ppriv, cpu);
+        SCHED_OP(new_ops, free_pdata, ppriv);
          return -ENOMEM;

@@ -1714,7 +1716,8 @@ int schedule_cpu_switch(unsigned int cpu, struct cpupool 
      SCHED_OP(new_ops, tick_resume, cpu);

      SCHED_OP(old_ops, free_vdata, vpriv_old);
-    SCHED_OP(old_ops, free_pdata, ppriv_old, cpu);
+    SCHED_OP(old_ops, deinit_pdata, ppriv_old, cpu);
+    SCHED_OP(old_ops, free_pdata, ppriv_old);

      per_cpu(cpupool, cpu) = c;
diff --git a/xen/include/xen/sched-if.h b/xen/include/xen/sched-if.h
index 1db7c8d..240f66c 100644
--- a/xen/include/xen/sched-if.h
+++ b/xen/include/xen/sched-if.h
@@ -135,9 +135,10 @@ struct scheduler {
      void         (*free_vdata)     (const struct scheduler *, void *);
      void *       (*alloc_vdata)    (const struct scheduler *, struct vcpu *,
                                      void *);
-    void         (*free_pdata)     (const struct scheduler *, void *, int);
+    void         (*free_pdata)     (const struct scheduler *, void *);
      void *       (*alloc_pdata)    (const struct scheduler *, int);
      void         (*init_pdata)     (const struct scheduler *, void *, int);
+    void         (*deinit_pdata)   (const struct scheduler *, void *, int);
      void         (*free_domdata)   (const struct scheduler *, void *);
      void *       (*alloc_domdata)  (const struct scheduler *, struct domain 

Julien Grall

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.