On Sat, 25 Oct 2025 12:00:16 -0400 Sasha Levin <[email protected]> wrote:
> - The change inserts `cond_resched()` inside the inner iteration over > every ftrace record (`kernel/trace/ftrace.c:7538`). That loop holds > the ftrace mutex and, for each record, invokes heavy helpers like > `test_for_valid_rec()` which in turn calls `kallsyms_lookup()` > (`kernel/trace/ftrace.c:4289`). On huge modules (e.g. amdgpu) this can > run for tens of milliseconds with preemption disabled, triggering the It got the "preemption disabled" wrong. Well maybe when running PREEMPT_NONE it is, but the description doesn't imply that. -- Steve > documented soft lockup/panic during module load. > - `ftrace_module_enable()` runs only in process context via > `prepare_coming_module()` (`kernel/module/main.c:3279`), so adding a > voluntary reschedule point is safe; the same pattern already exists in > other long-running ftrace loops (see commits d0b24b4e91fc and > 42ea22e754ba), so this brings consistency without changing control > flow or semantics. > - No data structures or interfaces change, and the code still executes > under the same locking (`ftrace_lock`, `text_mutex` when the arch > overrides `ftrace_arch_code_modify_prepare()`), so the risk of > regression is minimal: the new call simply yields CPU if needed while > keeping the locks held, preventing watchdog-induced crashes but > otherwise behaving identically.
