> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index ed455b53513b..336f40dc6618 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -1036,10 +1036,9 @@ trace_func_graph_ent_t ftrace_graph_entry =
> ftrace_graph_entry_stub;
> /* Try to assign a return stack array on FTRACE_RETSTACK_ALLOC_SIZE tasks. */
> static int alloc_retstack_tasklist(unsigned long **ret_stack_list)
> {
Does this comment still match the function's behavior? Before the patch,
alloc_retstack_tasklist() assigned at most FTRACE_RETSTACK_ALLOC_SIZE
stacks per call and returned -EAGAIN to trigger another batch. After the
patch, it walks every thread in one pass, allocating inline with
GFP_NOWAIT. The FTRACE_RETSTACK_ALLOC_SIZE pre-allocated entries are now
only a fallback when GFP_NOWAIT fails, and in the normal case they're all
freed at the free: label.
> - int i;
> - int ret = 0;
> int start = 0, end = FTRACE_RETSTACK_ALLOC_SIZE;
> struct task_struct *g, *t;
> + int i, ret = 0;
>
> if (WARN_ON_ONCE(!fgraph_stack_cachep))
> return -ENOMEM;
> @@ -1054,26 +1053,37 @@ static int alloc_retstack_tasklist(unsigned long
> **ret_stack_list)
> }
> }
>
> - rcu_read_lock();
> - for_each_process_thread(g, t) {
> - if (start == end) {
> - ret = -EAGAIN;
> - goto unlock;
> - }
> + scoped_guard (rcu) {
> + for_each_process_thread(g, t) {
> + unsigned long *rs;
> +
> + if (t->ret_stack)
> + continue;
> +
> + rs = kmem_cache_alloc(fgraph_stack_cachep, GFP_NOWAIT);
> + if (!rs) {
> + /*
> + * Returning from inside scoped_guard() drops
> + * the RCU read lock, but skips the free loop
> + * below. That is only safe because start ==
> + * end here, which leaves that loop nothing to
> + * free. Keep the two in step if this
> + * exhaustion check ever changes.
> + */
> + if (start == end)
> + return -EAGAIN;
> + rs = ret_stack_list[start++];
> + }
>
> - if (t->ret_stack == NULL) {
> atomic_set(&t->trace_overrun, 0);
> - ret_stack_init_task_vars(ret_stack_list[start]);
> + ret_stack_init_task_vars(rs);
> t->curr_ret_stack = 0;
> t->curr_ret_depth = -1;
> /* Make sure the tasks see the 0 first: */
> - smp_wmb();
> - t->ret_stack = ret_stack_list[start++];
> + smp_store_release(&t->ret_stack, rs);
> }
> }
>
> -unlock:
> - rcu_read_unlock();
> free:
> for (i = start; i < end; i++)
> kmem_cache_free(fgraph_stack_cachep, ret_stack_list[i]);
---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/36644771324
