Re: [PATCH 7.1.y] Revert "tracing: perf: Fix stale head for perf syscall tracing"

[Peter Jung <admin@ptr1337.dev>]

On 8/16/26 16:57, Steven Rostedt wrote:
> On Sun, 16 Aug 2026 15:31:01 +0200
> Peter Jung<admin@ptr1337.dev> wrote:
> 
>> This reverts commit be94a3a77e7eb99c53418de7d4a01bc7eb3f634e.
>>
>> The upstream commit was applied after commit 57918341dd19 ("bpf: Add
>> sleepable support for classic tracepoint programs"), which moved BPF
>> program execution before the per-CPU perf event list is checked.
>>
>> The 7.1.y implementation has not undergone that restructuring. It handles
>> BPF and perf consumers together, and already reloads the current CPU's
>> perf event list after syscall_get_data().
>>
>> As a result, the backport adds an unconditional hlist_empty() return before
>> bpf_prog_array_valid() is consulted. A syscall trace event can have a valid
>> BPF program array while the current CPU's perf event list is empty. In that
>> case the early return prevents the BPF program from running.
>>
>> This breaks BPF consumers of faultable syscall-enter tracepoints such as
>> sys_enter_execve. One observed consequence is that Proton VPN's app-based
>> split tunneling no longer receives exec argument events and therefore
>> cannot match newly started processes.
>>
>> Revert the stable backport. The existing head assignment below the removed
>> block preserves its intended stale-head protection while retaining the
>> previous BPF-aware handling.
> 
> OK, so the Fixes on the original commit be94a3a77e7e should have had:
> 
> Fixes: 57918341dd19 ("bpf: Add sleepable support for classic tracepoint programs")
> 
> Instead?
> 
> -- Steve
> 

Yes, this should fix it too, but has been not verified yet. I will run a 
test tomorrow and let you know.

Best,

Peter

> 
>> Fixes: be94a3a77e7e ("tracing: perf: Fix stale head for perf syscall tracing")
>> Cc:stable@vger.kernel.org
>> Assisted-by:Codex:gpt-5.6-sol
>> Signed-off-by: Peter Jung<admin@ptr1337.dev>
>> ---
>>   kernel/trace/trace_syscalls.c | 5 -----
>>   1 file changed, 5 deletions(-)
>>
>> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
>> index 8dcedff8429a..8ad72e17d8eb 100644
>> --- a/kernel/trace/trace_syscalls.c
>> +++ b/kernel/trace/trace_syscalls.c
>> @@ -1436,11 +1436,6 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
>>   		if (syscall_get_data(sys_data, args, &user_ptr,
>>   				     &size, user_sizes, &uargs, buf_size) < 0)
>>   			return;
>> -
>> -		/* The above may have caused a migration */
>> -		head = this_cpu_ptr(sys_data->enter_event->perf_events);
>> -		if (hlist_empty(head))
>> -			return;
>>   	}
>>   
>>   	head = this_cpu_ptr(sys_data->enter_event->perf_events);
>