On Mon, Sep 28, 2026 at 6:22 PM Vineet Gupta <[email protected]> wrote: > > On 9/28/26 6:03 PM, [email protected] wrote: > > Thank you for your contribution! Sashiko AI review found 1 potential > > issue(s) to consider: > > - [Low] cleanup: mixing goto-based error handling and scope-based cleanup > > -- > > > > commit a6de528fef00ef67da15965a7a8b3944fa92b053 > > Author: Vineet Gupta <[email protected]> > > Subject: tracing: fgraph: allocate shadow stacks inline with GFP_NOWAIT > > > > This commit aims to resolve performance regressions with ftrace graph > > tracing > > when there are a large number of tasks. It replaces the pre-allocated batch > > approach with inline allocation using GFP_NOWAIT, avoiding repeated sweeps > > of > > the task list. Additionally, it transitions the RCU read-side section to use > > scoped_guard(rcu) instead of manual rcu_read_lock and rcu_read_unlock calls. > > > >> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c > >> index 40d373d65f9b9..1c5ccc3f80d53 100644 > >> --- a/kernel/trace/fgraph.c > >> +++ b/kernel/trace/fgraph.c > > [ ... ] > >> @@ -1057,26 +1056,37 @@ 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) { > > [Severity: Low] > > Does this mix goto-based error handling and scope-based cleanup within the > > same > > function? > > > > Looking at alloc_retstack_tasklist(), the function retains the legacy goto > > free > > path in the initial pre-allocation loop (just before this block), while > > introducing scoped_guard(rcu) here. > > > > The cleanup subsystem guidelines recommend that for a given routine, we > > should > > convert all resources that need a goto cleanup to scope-based cleanup, or > > convert none of them. Mixing these paradigms creates confusing ownership > > semantics and is highly prone to double-free or resource leak regressions > > upon > > future modifications. > > > > Could we either convert the ret_stack_list array cleanup to use scope-based > > helpers, or stick to the manual rcu_read_lock() and rcu_read_unlock() here > > to > > keep the error handling style consistent? > > And a third option is to drop the fallback allocation completely and > return -EAGAIN and come back. Granted I don't have much experience of > typical handling of GFP_NOWAIT fails and retrying immediately: would > that recover at all or does that take us back to where we started ? Peter >
Not Peter, but I don't see a problem with scoped rcu and goto-based free/cleanup. Unless Peter objects, let's keep it as is? > Thx, > -Vineet
