On 2020-10-22 17:02, Peter Zijlstra wrote:
On Thu, Oct 22, 2020 at 04:27:52PM +0530, Sai Prakash Ranjan wrote:
Looking at the ETR and other places in the kernel, ETF and the ETB are the only places trying to dereference the task(owner) in tmc_enable_etf_sink_perf() which is also called from the sched_in path as in the call trace.
@@ -391,6 +392,10 @@ static void *tmc_alloc_etf_buffer(struct coresight_device *csdev, { int node; struct cs_buffers *buf;
- struct task_struct *task = READ_ONCE(event->owner);
- if (!task || is_kernel_event(event))
return NULL;This is *wrong*... why do you care about who owns the events?
The original issue was the owner being NULL and causing a NULL pointer dereference. I did ask some time back if it is valid for the owner to be NULL [1] and should probably be handled in events core?
[1] https://lore.kernel.org/lkml/c0e1f99a0a2480dfc8d788bb424d3f08@codeaurora.org...
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000548 Mem abort info: ESR = 0x96000006 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 Data abort info: ISV = 0, ISS = 0x00000006 CM = 0, WnR = 0 <snip>... Call trace: tmc_enable_etf_sink+0xe4/0x280 coresight_enable_path+0x168/0x1fc etm_event_start+0x8c/0xf8 etm_event_add+0x38/0x54 event_sched_in+0x194/0x2ac group_sched_in+0x54/0x12c flexible_sched_in+0xd8/0x120 visit_groups_merge+0x100/0x16c ctx_flexible_sched_in+0x50/0x74 ctx_sched_in+0xa4/0xa8 perf_event_sched_in+0x60/0x6c perf_event_context_sched_in+0x98/0xe0 __perf_event_task_sched_in+0x5c/0xd8 finish_task_switch+0x184/0x1cc schedule_tail+0x20/0xec ret_from_fork+0x4/0x18
Thanks, Sai