[PATCH v7 1/3] perf/core: Fix NULL pmu_ctx passed to pmu->sched_task()

[Puranjay Mohan <puranjay@kernel.org>]

perf_pmu_sched_task() returns early when cpuctx->task_ctx is set, and
cpc->task_epc is only non-NULL while a task context is scheduled in on
this CPU. __perf_pmu_sched_task() therefore always passes NULL:

  Unable to handle kernel NULL pointer dereference at virtual address 00
  pc : armv8pmu_sched_task+0x14/0x50
  Call trace:
   armv8pmu_sched_task+0x14/0x50 (P)
   perf_pmu_sched_task+0xac/0x108
   __perf_event_task_sched_out+0x6c/0xe0

Pass &cpc->epc instead, the CPU-wide context for this PMU, which the
function already dereferences a few lines up to find pmu.

armv8pmu_sched_task() is the only in-tree implementation that
dereferences the argument, and it only reads ->pmu, so the oops needs
BRBE, added in v6.17.

Fixes: bd2756811766 ("perf: Rewrite core context handling")
Cc: stable@vger.kernel.org
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4638544205f28..05635217696c2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3907,7 +3907,7 @@ static void __perf_pmu_sched_task(struct perf_cpu_pmu_context *cpc,
 	perf_ctx_lock(cpuctx, cpuctx->task_ctx);
 	perf_pmu_disable(pmu);
 
-	pmu->sched_task(cpc->task_epc, task, sched_in);
+	pmu->sched_task(&cpc->epc, task, sched_in);
 
 	perf_pmu_enable(pmu);
 	perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
-- 
2.53.0-Meta