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SubjectRe: perf: bug in rdpmc/mmap accounting after exec
On Wed, Jul 26, 2017 at 03:39:01PM -0400, Vince Weaver wrote:
> Hello
>
> so one last bug found by the PAPI testsuite.
>
> This one involves the rdpmc auto-disable on last unmap of an event
> feature.
>
> Failing test case:
>
> fd=perf_event_open();
> addr=mmap(fd);
> exec() // without closing or unmapping the event
> fd=perf_event_open();
> addr=mmap(fd);
> rdpmc() // GPFs due to rdpmc being disabled
>
> I won't pretend to be able to follow the rdpmc disabling code, but if I
> add some printks it looks like
> current->mm->context.perf_rdpmc_allowed
> isn't properly being reset on exec?
>
> In fact, current->mm->context.perf_rdpmc_allowed goes negative which seems
> like it shouldn't happen?
>
> Anyway, a test case for this can be found in the perf_event_tests,
> tests/rdpmc/rdpmc_exec_papi

Good find that...

The below seems to fix that for me.

---
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 8e3db8f642a7..3186f6e081c4 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2114,11 +2114,14 @@ static void refresh_pce(void *ignored)
load_mm_cr4(this_cpu_read(cpu_tlbstate.loaded_mm));
}

-static void x86_pmu_event_mapped(struct perf_event *event)
+static void x86_pmu_event_mapped(struct perf_event *event, struct vm_area_struct *vma)
{
+ struct mm_struct *mm;
+
if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED))
return;

+ mm = vma->vm_mm;
/*
* This function relies on not being called concurrently in two
* tasks in the same mm. Otherwise one task could observe
@@ -2129,22 +2132,21 @@ static void x86_pmu_event_mapped(struct perf_event *event)
* For now, this can't happen because all callers hold mmap_sem
* for write. If this changes, we'll need a different solution.
*/
- lockdep_assert_held_exclusive(&current->mm->mmap_sem);
+ lockdep_assert_held_exclusive(&mm->mmap_sem);

- if (atomic_inc_return(&current->mm->context.perf_rdpmc_allowed) == 1)
- on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1);
+ if (atomic_inc_return(&mm->context.perf_rdpmc_allowed) == 1)
+ on_each_cpu_mask(mm_cpumask(mm), refresh_pce, NULL, 1);
}

-static void x86_pmu_event_unmapped(struct perf_event *event)
+static void x86_pmu_event_unmapped(struct perf_event *event, struct vm_area_struct *vma)
{
- if (!current->mm)
- return;
+ struct mm_struct *mm = vma->vm_mm;

if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED))
return;

- if (atomic_dec_and_test(&current->mm->context.perf_rdpmc_allowed))
- on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1);
+ if (atomic_dec_and_test(&mm->context.perf_rdpmc_allowed))
+ on_each_cpu_mask(mm_cpumask(mm), refresh_pce, NULL, 1);
}

static int x86_pmu_event_idx(struct perf_event *event)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index a3b873fc59e4..271a32a7e3e1 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -310,8 +310,8 @@ struct pmu {
* Notification that the event was mapped or unmapped. Called
* in the context of the mapping task.
*/
- void (*event_mapped) (struct perf_event *event); /*optional*/
- void (*event_unmapped) (struct perf_event *event); /*optional*/
+ void (*event_mapped) (struct perf_event *event, struct vm_area_struct *vma); /*optional*/
+ void (*event_unmapped) (struct perf_event *event, struct vm_area_struct *vma); /*optional*/

/*
* Flags for ->add()/->del()/ ->start()/->stop(). There are
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 426c2ffba16d..f724348bba08 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5090,7 +5105,7 @@ static void perf_mmap_open(struct vm_area_struct *vma)
atomic_inc(&event->rb->aux_mmap_count);

if (event->pmu->event_mapped)
- event->pmu->event_mapped(event);
+ event->pmu->event_mapped(event, vma);
}

static void perf_pmu_output_stop(struct perf_event *event);
@@ -5113,7 +5128,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
unsigned long size = perf_data_size(rb);

if (event->pmu->event_unmapped)
- event->pmu->event_unmapped(event);
+ event->pmu->event_unmapped(event, vma);

/*
* rb->aux_mmap_count will always drop before rb->mmap_count and
@@ -5411,7 +5426,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
vma->vm_ops = &perf_mmap_vmops;

if (event->pmu->event_mapped)
- event->pmu->event_mapped(event);
+ event->pmu->event_mapped(event, vma);

return ret;
}
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