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@xxxxxxxxxxxxxx/
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
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