6.5-stable review patch. If anyone has any objections, please let me know.
------------------
From: Peter Zijlstra peterz@infradead.org
commit 889c58b3155ff4c8e8671c95daef63d6fabbb6b1 upstream.
Audit of the refcounting turned up that perf_pmu_migrate_context() fails to migrate the ctx refcount.
Fixes: bd2756811766 ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/perf_event.h | 13 ++++++++----- kernel/events/core.c | 17 +++++++++++++++++ 2 files changed, 25 insertions(+), 5 deletions(-)
--- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -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; --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4816,6 +4816,11 @@ find_get_pmu_context(struct pmu *pmu, st 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); @@ -12888,6 +12893,9 @@ static void __perf_pmu_install_event(str 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); @@ -12896,6 +12904,11 @@ static void __perf_pmu_install_event(str 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, @@ -12934,6 +12947,10 @@ void perf_pmu_migrate_context(struct pmu 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;