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

On Sun, 16 Aug 2026 15:31:01 +0200
Peter Jung <[email protected]> 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


> 
> Fixes: be94a3a77e7e ("tracing: perf: Fix stale head for perf syscall tracing")
> Cc: [email protected]
> Assisted-by: Codex:gpt-5.6-sol
> Signed-off-by: Peter Jung <[email protected]>
> ---
>  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);