The fix from 9fc81d87420d ("perf: Fix events installation during
moving group") was incomplete in that it failed to recognise that
creating a group with events for different CPUs is semantically
broken -- they cannot be co-scheduled.
Furthermore, it leads to real breakage where, when we create an event
for CPU Y and then migrate it to form a group on CPU X, the code gets
confused where the counter is programmed -- triggered by the fuzzer.
Fix this by tightening the rules for creating groups. Only allow
grouping of counters that can be co-scheduled in the same context.
This means for the same task and/or the same cpu.
Fixes: 9fc81d87420d ("perf: Fix events installation during moving group")
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
include/linux/perf_event.h | 6 ------
kernel/events/core.c | 15 +++++++++++++--
2 files changed, 13 insertions(+), 8 deletions(-)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -450,11 +450,6 @@ struct perf_event {
#endif /* CONFIG_PERF_EVENTS */
};
-enum perf_event_context_type {
- task_context,
- cpu_context,
-};
-
/**
* struct perf_event_context - event context structure
*
@@ -462,7 +457,6 @@ enum perf_event_context_type {
*/
struct perf_event_context {
struct pmu *pmu;
- enum perf_event_context_type type;
/*
* Protect the states of the events in the list,
* nr_active, and the list:
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6846,7 +6846,6 @@ int perf_pmu_register(struct pmu *pmu, c
__perf_event_init_context(&cpuctx->ctx);
lockdep_set_class(&cpuctx->ctx.mutex, &cpuctx_mutex);
lockdep_set_class(&cpuctx->ctx.lock, &cpuctx_lock);
- cpuctx->ctx.type = cpu_context;
cpuctx->ctx.pmu = pmu;
__perf_cpu_hrtimer_init(cpuctx, cpu);
@@ -7493,7 +7492,19 @@ SYSCALL_DEFINE5(perf_event_open,
* task or CPU context:
*/
if (move_group) {
- if (group_leader->ctx->type != ctx->type)
+ /*
+ * Make sure we're both on the same task, or both
+ * per-cpu events.
+ */
+ if (group_leader->ctx->task != ctx->task)
+ goto err_context;
+
+ /*
+ * Make sure we're both events for the same CPU;
+ * grouping events for different CPUs is broken; since
+ * you can never concurrently schedule them anyhow.
+ */
+ if (group_leader->cpu != event->cpu)
goto err_context;
} else {
if (group_leader->ctx != ctx)
--
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