[PATCH v2 0/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP

[PATCH v2 0/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP

[Dario Faggioli]

Hi,

This is v2 of https://lists.xen.org/archives/html/xen-devel/2017-03/msg02119.html

It's now two patches. Patch 1 is what I already sent, amended taking into
account Jan's suggesions. It is the actual bugfix and the one that should be
backported.

Patch 2 is basically applying the same principle to the DOM2OP() macro, which
although not buggy, was equally unclear and potentially dangerous (plus some
renaming, suggested by Juergen).

Thanks and Regards,
Dario
---
Dario Faggioli (2):
      xen: sched: don't call hooks of the wrong scheduler via VCPU2OP
      xen: sched: improve robustness (and rename) DOM2OP()

 xen/common/schedule.c |   76 +++++++++++++++++++++++++++++++++++++------------
 1 file changed, 57 insertions(+), 19 deletions(-)
--
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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[PATCH v2 1/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP

[Dario Faggioli]

Within context_saved(), we call the context_saved hook,
and we use VCPU2OP() to determine from what scheduler.
VCPU2OP uses DOM2OP, which uses d->cpupool, which is
NULL when d is the idle domain. And in that case,
DOM2OP just returns ops, the scheduler of cpupool0.

Therefore, if:
- cpupool0's scheduler defines context_saved (like
  Credit2 and RTDS do),
- we are not in cpupool0 (i.e., our scheduler is
  not ops),
- we are context switching from idle,

we call VCPU2OP(idle_vcpu), which means
DOM2OP(idle->cpupool), which is ops.

Therefore, we both:
- check if context_saved is defined in the wrong
  scheduler;
- if yes, call the wrong one.

When using Credit2 at boot, and also Credit2 in
the other cpupool, this is wrong but innocuous,
because it only involves the idle vcpus.

When using Credit2 at boot, and Credit1 in the
other cpupool, this is *totally* wrong, and
it's by chance it does not explode!

When using Credit2 and other schedulers I'm
developping, I hit the following assert (in
sched_credit2.c, on a CPU inside a cpupool that
does not use Credit2):

csched2_context_saved()
{
 ...
 ASSERT(!vcpu_on_runq(svc));
 ...
}

Fix this by dealing explicitly, in VCPU2OP, with
idle vcpus, returning the scheduler of the pCPU
they (always) run on.

While there, rename VCPU2OP itself to something
that makes it easier to understand what it does.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
---
Cc: George Dunlap <george.dunlap@citrix.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Jan Beulich <jbeulich@suse.com>
---
Changes from v1:
 - refactored according to review comments. Added code comments and an ASSERT().
---
Cc-ing Jan, as this should be backported at least to 4.8, but, IMO, as back as
possible.
---
 xen/common/schedule.c |   22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 223a120..d344b7c 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -78,7 +78,27 @@ static struct scheduler __read_mostly ops;
           : (typeof((opsptr)->fn(opsptr, ##__VA_ARGS__)))0 )
 
 #define DOM2OP(_d)    (((_d)->cpupool == NULL) ? &ops : ((_d)->cpupool->sched))
-#define VCPU2OP(_v)   (DOM2OP((_v)->domain))
+static inline struct scheduler *VCPU2OP(const struct vcpu *v)
+{
+    struct domain *d = v->domain;
+
+    if ( likely(d->cpupool != NULL) )
+        return d->cpupool->sched;
+
+    /*
+     * If d->cpupool is NULL, this is a vCPU of the idle domain. And this
+     * case is special because the idle domain does not really belong to
+     * a cpupool and, hence, doesn't really have a scheduler). In fact, its
+     * vCPUs (may) run on pCPUs which are in different pools, with different
+     * schedulers.
+     *
+     * What we want, in this case, is the scheduler of the pCPU where this
+     * particular idle vCPU is running. And, since v->processor never changes
+     * for idle vCPUs, it is safe to use it, with no locks, to figure that out.
+     */
+    ASSERT(is_idle_domain(d));
+    return per_cpu(scheduler, v->processor);
+}
 #define VCPU2ONLINE(_v) cpupool_domain_cpumask((_v)->domain)
 
 static inline void trace_runstate_change(struct vcpu *v, int new_state)


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Re: [PATCH v2 1/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP

[Juergen Gross]

On 17/03/17 19:19, Dario Faggioli wrote:
> Within context_saved(), we call the context_saved hook,
> and we use VCPU2OP() to determine from what scheduler.
> VCPU2OP uses DOM2OP, which uses d->cpupool, which is
> NULL when d is the idle domain. And in that case,
> DOM2OP just returns ops, the scheduler of cpupool0.
> 
> Therefore, if:
> - cpupool0's scheduler defines context_saved (like
>   Credit2 and RTDS do),
> - we are not in cpupool0 (i.e., our scheduler is
>   not ops),
> - we are context switching from idle,
> 
> we call VCPU2OP(idle_vcpu), which means
> DOM2OP(idle->cpupool), which is ops.
> 
> Therefore, we both:
> - check if context_saved is defined in the wrong
>   scheduler;
> - if yes, call the wrong one.
> 
> When using Credit2 at boot, and also Credit2 in
> the other cpupool, this is wrong but innocuous,
> because it only involves the idle vcpus.
> 
> When using Credit2 at boot, and Credit1 in the
> other cpupool, this is *totally* wrong, and
> it's by chance it does not explode!
> 
> When using Credit2 and other schedulers I'm
> developping, I hit the following assert (in
> sched_credit2.c, on a CPU inside a cpupool that
> does not use Credit2):
> 
> csched2_context_saved()
> {
>  ...
>  ASSERT(!vcpu_on_runq(svc));
>  ...
> }
> 
> Fix this by dealing explicitly, in VCPU2OP, with
> idle vcpus, returning the scheduler of the pCPU
> they (always) run on.
> 
> While there, rename VCPU2OP itself to something
> that makes it easier to understand what it does.
> 
> Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen


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Re: [PATCH v2 1/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP

[Juergen Gross]

On 17/03/17 19:19, Dario Faggioli wrote:
> Within context_saved(), we call the context_saved hook,
> and we use VCPU2OP() to determine from what scheduler.
> VCPU2OP uses DOM2OP, which uses d->cpupool, which is
> NULL when d is the idle domain. And in that case,
> DOM2OP just returns ops, the scheduler of cpupool0.
> 
> Therefore, if:
> - cpupool0's scheduler defines context_saved (like
>   Credit2 and RTDS do),
> - we are not in cpupool0 (i.e., our scheduler is
>   not ops),
> - we are context switching from idle,
> 
> we call VCPU2OP(idle_vcpu), which means
> DOM2OP(idle->cpupool), which is ops.
> 
> Therefore, we both:
> - check if context_saved is defined in the wrong
>   scheduler;
> - if yes, call the wrong one.
> 
> When using Credit2 at boot, and also Credit2 in
> the other cpupool, this is wrong but innocuous,
> because it only involves the idle vcpus.
> 
> When using Credit2 at boot, and Credit1 in the
> other cpupool, this is *totally* wrong, and
> it's by chance it does not explode!
> 
> When using Credit2 and other schedulers I'm
> developping, I hit the following assert (in
> sched_credit2.c, on a CPU inside a cpupool that
> does not use Credit2):
> 
> csched2_context_saved()
> {
>  ...
>  ASSERT(!vcpu_on_runq(svc));
>  ...
> }
> 
> Fix this by dealing explicitly, in VCPU2OP, with
> idle vcpus, returning the scheduler of the pCPU
> they (always) run on.
> 
> While there, rename VCPU2OP itself to something
> that makes it easier to understand what it does.
> 
> Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen


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Re: [PATCH v2 1/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP

[Jan Beulich]

>>> On 17.03.17 at 19:29, <jgross@suse.com> wrote:
> On 17/03/17 19:19, Dario Faggioli wrote:
>> Within context_saved(), we call the context_saved hook,
>> and we use VCPU2OP() to determine from what scheduler.
>> VCPU2OP uses DOM2OP, which uses d->cpupool, which is
>> NULL when d is the idle domain. And in that case,
>> DOM2OP just returns ops, the scheduler of cpupool0.
>> 
>> Therefore, if:
>> - cpupool0's scheduler defines context_saved (like
>>   Credit2 and RTDS do),
>> - we are not in cpupool0 (i.e., our scheduler is
>>   not ops),
>> - we are context switching from idle,
>> 
>> we call VCPU2OP(idle_vcpu), which means
>> DOM2OP(idle->cpupool), which is ops.
>> 
>> Therefore, we both:
>> - check if context_saved is defined in the wrong
>>   scheduler;
>> - if yes, call the wrong one.
>> 
>> When using Credit2 at boot, and also Credit2 in
>> the other cpupool, this is wrong but innocuous,
>> because it only involves the idle vcpus.
>> 
>> When using Credit2 at boot, and Credit1 in the
>> other cpupool, this is *totally* wrong, and
>> it's by chance it does not explode!
>> 
>> When using Credit2 and other schedulers I'm
>> developping, I hit the following assert (in
>> sched_credit2.c, on a CPU inside a cpupool that
>> does not use Credit2):
>> 
>> csched2_context_saved()
>> {
>>  ...
>>  ASSERT(!vcpu_on_runq(svc));
>>  ...
>> }
>> 
>> Fix this by dealing explicitly, in VCPU2OP, with
>> idle vcpus, returning the scheduler of the pCPU
>> they (always) run on.
>> 
>> While there, rename VCPU2OP itself to something
>> that makes it easier to understand what it does.
>> 
>> Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
> 
> Reviewed-by: Juergen Gross <jgross@suse.com>

This came through twice, so I'm now wondering whether one of
them was meant for 2/2, or whether this was just some
infrastructure glitch.

Jan


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Re: [PATCH v2 1/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP

[George Dunlap]

On 17/03/17 18:19, Dario Faggioli wrote:
> Within context_saved(), we call the context_saved hook,
> and we use VCPU2OP() to determine from what scheduler.
> VCPU2OP uses DOM2OP, which uses d->cpupool, which is
> NULL when d is the idle domain. And in that case,
> DOM2OP just returns ops, the scheduler of cpupool0.
> 
> Therefore, if:
> - cpupool0's scheduler defines context_saved (like
>   Credit2 and RTDS do),
> - we are not in cpupool0 (i.e., our scheduler is
>   not ops),
> - we are context switching from idle,
> 
> we call VCPU2OP(idle_vcpu), which means
> DOM2OP(idle->cpupool), which is ops.
> 
> Therefore, we both:
> - check if context_saved is defined in the wrong
>   scheduler;
> - if yes, call the wrong one.
> 
> When using Credit2 at boot, and also Credit2 in
> the other cpupool, this is wrong but innocuous,
> because it only involves the idle vcpus.
> 
> When using Credit2 at boot, and Credit1 in the
> other cpupool, this is *totally* wrong, and
> it's by chance it does not explode!
> 
> When using Credit2 and other schedulers I'm
> developping, I hit the following assert (in
> sched_credit2.c, on a CPU inside a cpupool that
> does not use Credit2):
> 
> csched2_context_saved()
> {
>  ...
>  ASSERT(!vcpu_on_runq(svc));
>  ...
> }
> 
> Fix this by dealing explicitly, in VCPU2OP, with
> idle vcpus, returning the scheduler of the pCPU
> they (always) run on.
> 
> While there, rename VCPU2OP itself to something
> that makes it easier to understand what it does.
> 
> Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>

Reviewed-by: George Dunlap <george.dunlap@citrix.com>


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Re: [PATCH v2 1/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP

[George Dunlap]

On 17/03/17 18:19, Dario Faggioli wrote:
> Within context_saved(), we call the context_saved hook,
> and we use VCPU2OP() to determine from what scheduler.
> VCPU2OP uses DOM2OP, which uses d->cpupool, which is
> NULL when d is the idle domain. And in that case,
> DOM2OP just returns ops, the scheduler of cpupool0.
> 
> Therefore, if:
> - cpupool0's scheduler defines context_saved (like
>   Credit2 and RTDS do),
> - we are not in cpupool0 (i.e., our scheduler is
>   not ops),
> - we are context switching from idle,
> 
> we call VCPU2OP(idle_vcpu), which means
> DOM2OP(idle->cpupool), which is ops.
> 
> Therefore, we both:
> - check if context_saved is defined in the wrong
>   scheduler;
> - if yes, call the wrong one.
> 
> When using Credit2 at boot, and also Credit2 in
> the other cpupool, this is wrong but innocuous,
> because it only involves the idle vcpus.
> 
> When using Credit2 at boot, and Credit1 in the
> other cpupool, this is *totally* wrong, and
> it's by chance it does not explode!
> 
> When using Credit2 and other schedulers I'm
> developping, I hit the following assert (in
> sched_credit2.c, on a CPU inside a cpupool that
> does not use Credit2):
> 
> csched2_context_saved()
> {
>  ...
>  ASSERT(!vcpu_on_runq(svc));
>  ...
> }
> 
> Fix this by dealing explicitly, in VCPU2OP, with
> idle vcpus, returning the scheduler of the pCPU
> they (always) run on.
> 
> While there, rename VCPU2OP itself to something
> that makes it easier to understand what it does.

This seems to have been moved into patch 2/2 -- I'll remove this
paragraph on commit if that's OK with you.

 -George


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Re: [PATCH v2 1/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP

[Dario Faggioli]

[-- Attachment #1.1: Type: text/plain, Size: 817 bytes --]

On Mon, 2017-03-27 at 12:49 +0100, George Dunlap wrote:
> On 17/03/17 18:19, Dario Faggioli wrote:
> > Fix this by dealing explicitly, in VCPU2OP, with
> > idle vcpus, returning the scheduler of the pCPU
> > they (always) run on.
> > 
> > While there, rename VCPU2OP itself to something
> > that makes it easier to understand what it does.
> 
> This seems to have been moved into patch 2/2 -- I'll remove this
> paragraph on commit if that's OK with you.
> 
Mmm... Yes, sorry for this.

I'm ok with you dropping the paragraph. Thanks.

Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

[-- Attachment #1.2: This is a digitally signed message part --]
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[PATCH v2 2/2] xen: sched: improve robustness (and rename) DOM2OP()

[Dario Faggioli]

Clarify and enforce (with ASSERTs) when the function
is called on the idle domain, and explain in comments
what it means and when it is ok to do so.

While there, change the name of the function to a more
self-explanatory one, and do the same to VCPU2OP.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
---
Cc: George Dunlap <george.dunlap@citrix.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Jan Beulich <jbeulich@suse.com>
---
Changes from v1:
 - new patch;
 - renamed VCPU2OP, as suggested during v1's review of patch 1.
---
 xen/common/schedule.c |   56 ++++++++++++++++++++++++++++++++-----------------
 1 file changed, 37 insertions(+), 19 deletions(-)

diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index d344b7c..fdb8ff4 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -77,8 +77,25 @@ static struct scheduler __read_mostly ops;
          (( (opsptr)->fn != NULL ) ? (opsptr)->fn(opsptr, ##__VA_ARGS__ )  \
           : (typeof((opsptr)->fn(opsptr, ##__VA_ARGS__)))0 )
 
-#define DOM2OP(_d)    (((_d)->cpupool == NULL) ? &ops : ((_d)->cpupool->sched))
-static inline struct scheduler *VCPU2OP(const struct vcpu *v)
+static inline struct scheduler *dom_get_scheduler(const struct domain *d)
+{
+    if ( likely(d->cpupool != NULL) )
+        return d->cpupool->sched;
+
+    /*
+     * If d->cpupool is NULL, this is the idle domain. This is special
+     * because the idle domain does not really bolong to any cpupool, and,
+     * hence, does not really have a scheduler.
+     *
+     * This is (should be!) only called like this for allocating the idle
+     * vCPUs for the first time, during boot, in which case what we want
+     * is the default scheduler that has been, choosen at boot.
+     */
+    ASSERT(is_idle_domain(d));
+    return &ops;
+}
+
+static inline struct scheduler *vcpu_get_scheduler(const struct vcpu *v)
 {
     struct domain *d = v->domain;
 
@@ -260,7 +277,8 @@ int sched_init_vcpu(struct vcpu *v, unsigned int processor)
     init_timer(&v->poll_timer, poll_timer_fn,
                v, v->processor);
 
-    v->sched_priv = SCHED_OP(DOM2OP(d), alloc_vdata, v, d->sched_priv);
+    v->sched_priv = SCHED_OP(dom_get_scheduler(d), alloc_vdata, v,
+		             d->sched_priv);
     if ( v->sched_priv == NULL )
         return 1;
 
@@ -272,7 +290,7 @@ int sched_init_vcpu(struct vcpu *v, unsigned int processor)
     }
     else
     {
-        SCHED_OP(DOM2OP(d), insert_vcpu, v);
+        SCHED_OP(dom_get_scheduler(d), insert_vcpu, v);
     }
 
     return 0;
@@ -326,7 +344,7 @@ int sched_move_domain(struct domain *d, struct cpupool *c)
 
     domain_pause(d);
 
-    old_ops = DOM2OP(d);
+    old_ops = dom_get_scheduler(d);
     old_domdata = d->sched_priv;
 
     for_each_vcpu ( d, v )
@@ -389,8 +407,8 @@ void sched_destroy_vcpu(struct vcpu *v)
     kill_timer(&v->poll_timer);
     if ( test_and_clear_bool(v->is_urgent) )
         atomic_dec(&per_cpu(schedule_data, v->processor).urgent_count);
-    SCHED_OP(VCPU2OP(v), remove_vcpu, v);
-    SCHED_OP(VCPU2OP(v), free_vdata, v->sched_priv);
+    SCHED_OP(vcpu_get_scheduler(v), remove_vcpu, v);
+    SCHED_OP(vcpu_get_scheduler(v), free_vdata, v->sched_priv);
 }
 
 int sched_init_domain(struct domain *d, int poolid)
@@ -404,7 +422,7 @@ int sched_init_domain(struct domain *d, int poolid)
 
     SCHED_STAT_CRANK(dom_init);
     TRACE_1D(TRC_SCHED_DOM_ADD, d->domain_id);
-    return SCHED_OP(DOM2OP(d), init_domain, d);
+    return SCHED_OP(dom_get_scheduler(d), init_domain, d);
 }
 
 void sched_destroy_domain(struct domain *d)
@@ -413,7 +431,7 @@ void sched_destroy_domain(struct domain *d)
 
     SCHED_STAT_CRANK(dom_destroy);
     TRACE_1D(TRC_SCHED_DOM_REM, d->domain_id);
-    SCHED_OP(DOM2OP(d), destroy_domain, d);
+    SCHED_OP(dom_get_scheduler(d), destroy_domain, d);
 
     cpupool_rm_domain(d);
 }
@@ -432,7 +450,7 @@ void vcpu_sleep_nosync(struct vcpu *v)
         if ( v->runstate.state == RUNSTATE_runnable )
             vcpu_runstate_change(v, RUNSTATE_offline, NOW());
 
-        SCHED_OP(VCPU2OP(v), sleep, v);
+        SCHED_OP(vcpu_get_scheduler(v), sleep, v);
     }
 
     vcpu_schedule_unlock_irqrestore(lock, flags, v);
@@ -461,7 +479,7 @@ void vcpu_wake(struct vcpu *v)
     {
         if ( v->runstate.state >= RUNSTATE_blocked )
             vcpu_runstate_change(v, RUNSTATE_runnable, NOW());
-        SCHED_OP(VCPU2OP(v), wake, v);
+        SCHED_OP(vcpu_get_scheduler(v), wake, v);
     }
     else if ( !(v->pause_flags & VPF_blocked) )
     {
@@ -516,8 +534,8 @@ static void vcpu_move_locked(struct vcpu *v, unsigned int new_cpu)
      * Actual CPU switch to new CPU.  This is safe because the lock
      * pointer cant' change while the current lock is held.
      */
-    if ( VCPU2OP(v)->migrate )
-        SCHED_OP(VCPU2OP(v), migrate, v, new_cpu);
+    if ( vcpu_get_scheduler(v)->migrate )
+        SCHED_OP(vcpu_get_scheduler(v), migrate, v, new_cpu);
     else
         v->processor = new_cpu;
 }
@@ -583,7 +601,7 @@ static void vcpu_migrate(struct vcpu *v)
                 break;
 
             /* Select a new CPU. */
-            new_cpu = SCHED_OP(VCPU2OP(v), pick_cpu, v);
+            new_cpu = SCHED_OP(vcpu_get_scheduler(v), pick_cpu, v);
             if ( (new_lock == per_cpu(schedule_data, new_cpu).schedule_lock) &&
                  cpumask_test_cpu(new_cpu, v->domain->cpupool->cpu_valid) )
                 break;
@@ -685,7 +703,7 @@ void restore_vcpu_affinity(struct domain *d)
         spin_unlock_irq(lock);;
 
         lock = vcpu_schedule_lock_irq(v);
-        v->processor = SCHED_OP(VCPU2OP(v), pick_cpu, v);
+        v->processor = SCHED_OP(vcpu_get_scheduler(v), pick_cpu, v);
         spin_unlock_irq(lock);
     }
 
@@ -975,7 +993,7 @@ long vcpu_yield(void)
     struct vcpu * v=current;
     spinlock_t *lock = vcpu_schedule_lock_irq(v);
 
-    SCHED_OP(VCPU2OP(v), yield, v);
+    SCHED_OP(vcpu_get_scheduler(v), yield, v);
     vcpu_schedule_unlock_irq(lock, v);
 
     SCHED_STAT_CRANK(vcpu_yield);
@@ -1288,7 +1306,7 @@ long sched_adjust(struct domain *d, struct xen_domctl_scheduler_op *op)
     if ( ret )
         return ret;
 
-    if ( op->sched_id != DOM2OP(d)->sched_id )
+    if ( op->sched_id != dom_get_scheduler(d)->sched_id )
         return -EINVAL;
 
     switch ( op->cmd )
@@ -1304,7 +1322,7 @@ long sched_adjust(struct domain *d, struct xen_domctl_scheduler_op *op)
 
     /* NB: the pluggable scheduler code needs to take care
      * of locking by itself. */
-    if ( (ret = SCHED_OP(DOM2OP(d), adjust, d, op)) == 0 )
+    if ( (ret = SCHED_OP(dom_get_scheduler(d), adjust, d, op)) == 0 )
         TRACE_1D(TRC_SCHED_ADJDOM, d->domain_id);
 
     return ret;
@@ -1482,7 +1500,7 @@ void context_saved(struct vcpu *prev)
     /* Check for migration request /after/ clearing running flag. */
     smp_mb();
 
-    SCHED_OP(VCPU2OP(prev), context_saved, prev);
+    SCHED_OP(vcpu_get_scheduler(prev), context_saved, prev);
 
     if ( unlikely(prev->pause_flags & VPF_migrating) )
         vcpu_migrate(prev);


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Re: [PATCH v2 2/2] xen: sched: improve robustness (and rename) DOM2OP()

[George Dunlap]

On 17/03/17 18:19, Dario Faggioli wrote:
> Clarify and enforce (with ASSERTs) when the function
> is called on the idle domain, and explain in comments
> what it means and when it is ok to do so.
> 
> While there, change the name of the function to a more
> self-explanatory one, and do the same to VCPU2OP.
> 
> Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
> ---
> Cc: George Dunlap <george.dunlap@citrix.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Jan Beulich <jbeulich@suse.com>
> ---
> Changes from v1:
>  - new patch;
>  - renamed VCPU2OP, as suggested during v1's review of patch 1.
> ---
>  xen/common/schedule.c |   56 ++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 37 insertions(+), 19 deletions(-)
> 
> diff --git a/xen/common/schedule.c b/xen/common/schedule.c
> index d344b7c..fdb8ff4 100644
> --- a/xen/common/schedule.c
> +++ b/xen/common/schedule.c
> @@ -77,8 +77,25 @@ static struct scheduler __read_mostly ops;
>           (( (opsptr)->fn != NULL ) ? (opsptr)->fn(opsptr, ##__VA_ARGS__ )  \
>            : (typeof((opsptr)->fn(opsptr, ##__VA_ARGS__)))0 )
>  
> -#define DOM2OP(_d)    (((_d)->cpupool == NULL) ? &ops : ((_d)->cpupool->sched))
> -static inline struct scheduler *VCPU2OP(const struct vcpu *v)
> +static inline struct scheduler *dom_get_scheduler(const struct domain *d)

Hmm -- I agree that VCPU2OP is probably not the right name, but I'm not
a fan of the new name either; and I don't have an option I like better yet.

With your permission I'll check in the first patch and come back to this.

 -George


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Re: [PATCH v2 2/2] xen: sched: improve robustness (and rename) DOM2OP()

[Dario Faggioli]

[-- Attachment #1.1: Type: text/plain, Size: 1570 bytes --]

On Mon, 2017-03-27 at 14:23 +0100, George Dunlap wrote:
> On 17/03/17 18:19, Dario Faggioli wrote:
> > --- a/xen/common/schedule.c
> > +++ b/xen/common/schedule.c
> > @@ -77,8 +77,25 @@ static struct scheduler __read_mostly ops;
> >           (( (opsptr)->fn != NULL ) ? (opsptr)->fn(opsptr,
> > ##__VA_ARGS__ )  \
> >            : (typeof((opsptr)->fn(opsptr, ##__VA_ARGS__)))0 )
> >  
> > -#define DOM2OP(_d)    (((_d)->cpupool == NULL) ? &ops : ((_d)-
> > >cpupool->sched))
> > -static inline struct scheduler *VCPU2OP(const struct vcpu *v)
> > +static inline struct scheduler *dom_get_scheduler(const struct
> > domain *d)
> 
> Hmm -- I agree that VCPU2OP is probably not the right name, but I'm
> not
> a fan of the new name either; and I don't have an option I like
> better yet.
> 
> With your permission I'll check in the first patch and come back to
> this.
> 
Ok. The renaming was the least important part of what is done in this
patch.

But indeed I do think that, while here, we should take the chance the
names as well (especially considering they won't be macro, so the "all
capital letters" should go).

But, sure, go ahead with the first patch... I'll try to think and
propose a better name when/if I'll fine one. :-)

Thanks,
Dario
-- 
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-----------------------------------------------------------------
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Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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Re: [PATCH v2 2/2] xen: sched: improve robustness (and rename) DOM2OP()

[Dario Faggioli]

[-- Attachment #1.1: Type: text/plain, Size: 1458 bytes --]

On Mon, 2017-03-27 at 14:23 +0100, George Dunlap wrote:
> On 17/03/17 18:19, Dario Faggioli wrote:
> > --- a/xen/common/schedule.c
> > +++ b/xen/common/schedule.c
> > @@ -77,8 +77,25 @@ static struct scheduler __read_mostly ops;
> >           (( (opsptr)->fn != NULL ) ? (opsptr)->fn(opsptr,
> > ##__VA_ARGS__ )  \
> >            : (typeof((opsptr)->fn(opsptr, ##__VA_ARGS__)))0 )
> >  
> > -#define DOM2OP(_d)    (((_d)->cpupool == NULL) ? &ops : ((_d)-
> > >cpupool->sched))
> > -static inline struct scheduler *VCPU2OP(const struct vcpu *v)
> > +static inline struct scheduler *dom_get_scheduler(const struct
> > domain *d)
> 
> Hmm -- I agree that VCPU2OP is probably not the right name, but I'm
> not
> a fan of the new name either; and I don't have an option I like
> better yet.
> 
Maybe:

domain_scheduler()
vcpu_scheduler()

or

dom_scheduler()
vcpu_scheduler()

I.e., basically getting rid of the 'get' part, which may misleadingly
hint at some kind of reference counting.

Or, also trading 'scheduler' for 'ops':

dom_ops()
vcpu_ops()

This is all I can come up with, my preference being
{dom,vcpu}_scheduler().

Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
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Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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Re: [PATCH v2 2/2] xen: sched: improve robustness (and rename) DOM2OP()

[Juergen Gross]

On 06/04/17 12:59, Dario Faggioli wrote:
> On Mon, 2017-03-27 at 14:23 +0100, George Dunlap wrote:
>> On 17/03/17 18:19, Dario Faggioli wrote:
>>> --- a/xen/common/schedule.c
>>> +++ b/xen/common/schedule.c
>>> @@ -77,8 +77,25 @@ static struct scheduler __read_mostly ops;
>>>           (( (opsptr)->fn != NULL ) ? (opsptr)->fn(opsptr,
>>> ##__VA_ARGS__ )  \
>>>            : (typeof((opsptr)->fn(opsptr, ##__VA_ARGS__)))0 )
>>>  
>>> -#define DOM2OP(_d)    (((_d)->cpupool == NULL) ? &ops : ((_d)-
>>>> cpupool->sched))
>>> -static inline struct scheduler *VCPU2OP(const struct vcpu *v)
>>> +static inline struct scheduler *dom_get_scheduler(const struct
>>> domain *d)
>>
>> Hmm -- I agree that VCPU2OP is probably not the right name, but I'm
>> not
>> a fan of the new name either; and I don't have an option I like
>> better yet.
>>
> Maybe:
> 
> domain_scheduler()
> vcpu_scheduler()
> 
> or
> 
> dom_scheduler()
> vcpu_scheduler()
> 
> I.e., basically getting rid of the 'get' part, which may misleadingly
> hint at some kind of reference counting.
> 
> Or, also trading 'scheduler' for 'ops':
> 
> dom_ops()
> vcpu_ops()

sched_ops_dom()
sched_ops_vcpu()

or

sched_dom_ops()
sched_vcpu_ops()


Juergen

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Re: [PATCH v2 2/2] xen: sched: improve robustness (and rename) DOM2OP()

[Dario Faggioli]

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On Thu, 2017-04-06 at 13:06 +0200, Juergen Gross wrote:
> On 06/04/17 12:59, Dario Faggioli wrote:
> > Maybe:
> > 
> > domain_scheduler()
> > vcpu_scheduler()
> > 
> > or
> > 
> > dom_scheduler()
> > vcpu_scheduler()
> > 
> > Or, also trading 'scheduler' for 'ops':
> > 
> > dom_ops()
> > vcpu_ops()
> 
> sched_ops_dom()
> sched_ops_vcpu()
> 
> or
> 
> sched_dom_ops()
> sched_vcpu_ops()
> 
Yeah, these too.

So, for now, I've resent using dom_scheduler() and vcpu_scheduler().

But I'm happy to change them to whatever and re-send again, as soon as
George tells me which one is his preferred solution. :-D

Thanks and Regards,
Dario
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-----------------------------------------------------------------
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Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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