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perf/core: Fix cpuctx refcounting

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Audit of the refcounting turned up that perf_pmu_migrate_context()
fails to migrate the ctx refcount.

Fixes: bd27568117 ("perf: Rewrite core context handling")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20230612093539.085862001@infradead.org
Cc: <stable@vger.kernel.org>
This commit is contained in:
Peter Zijlstra 2023-06-09 12:34:46 +02:00 committed by Ingo Molnar
parent b85ea95d08
commit 889c58b315
2 changed files with 25 additions and 5 deletions
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13
include/linux/perf_event.h
View File

@ -843,11 +843,11 @@ struct perf_event {
};
/*
* ,-----------------------[1:n]----------------------.
* V V
* perf_event_context <-[1:n]-> perf_event_pmu_context <--- perf_event
* ^ ^ | |
* `--------[1:n]---------' `-[n:1]-> pmu <-[1:n]-'
* ,-----------------------[1:n]------------------------.
* V V
* perf_event_context <-[1:n]-> perf_event_pmu_context <-[1:n]- perf_event
* | |
* `--[n:1]-> pmu <-[1:n]--'
*
*
* struct perf_event_pmu_context lifetime is refcount based and RCU freed
@ -865,6 +865,9 @@ struct perf_event {
* ctx->mutex pinning the configuration. Since we hold a reference on
* group_leader (through the filedesc) it can't go away, therefore it's
* associated pmu_ctx must exist and cannot change due to ctx->mutex.
*
* perf_event holds a refcount on perf_event_context
* perf_event holds a refcount on perf_event_pmu_context
*/
struct perf_event_pmu_context {
struct pmu *pmu;

17
kernel/events/core.c
View File

@ -4828,6 +4828,11 @@ find_get_pmu_context(struct pmu *pmu, struct perf_event_context *ctx,
void *task_ctx_data = NULL;
if (!ctx->task) {
/*
* perf_pmu_migrate_context() / __perf_pmu_install_event()
* relies on the fact that find_get_pmu_context() cannot fail
* for CPU contexts.
*/
struct perf_cpu_pmu_context *cpc;
cpc = per_cpu_ptr(pmu->cpu_pmu_context, event->cpu);
@ -12889,6 +12894,9 @@ static void __perf_pmu_install_event(struct pmu *pmu,
int cpu, struct perf_event *event)
{
struct perf_event_pmu_context *epc;
struct perf_event_context *old_ctx = event->ctx;
get_ctx(ctx); /* normally find_get_context() */
event->cpu = cpu;
epc = find_get_pmu_context(pmu, ctx, event);
@ -12897,6 +12905,11 @@ static void __perf_pmu_install_event(struct pmu *pmu,
if (event->state >= PERF_EVENT_STATE_OFF)
event->state = PERF_EVENT_STATE_INACTIVE;
perf_install_in_context(ctx, event, cpu);
/*
* Now that event->ctx is updated and visible, put the old ctx.
*/
put_ctx(old_ctx);
}
static void __perf_pmu_install(struct perf_event_context *ctx,
@ -12935,6 +12948,10 @@ void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu)
struct perf_event_context *src_ctx, *dst_ctx;
LIST_HEAD(events);
/*
* Since per-cpu context is persistent, no need to grab an extra
* reference.
*/
src_ctx = &per_cpu_ptr(&perf_cpu_context, src_cpu)->ctx;
dst_ctx = &per_cpu_ptr(&perf_cpu_context, dst_cpu)->ctx;