On Tue, 23 Sep 2025 18:59:07 +0200 Michal Koutný <[email protected]> wrote:
> If ever PID_MAX_DEFAULT changes, it must be compatible with tracing > hashmaps assumptions. > > Link: https://lore.kernel.org/r/[email protected]/ > Signed-off-by: Michal Koutný <[email protected]> > --- > kernel/trace/trace_sched_switch.c | 2 ++ > 1 file changed, 2 insertions(+) > > Drive-by flushing an old idea. Take it or leave it. > > diff --git a/kernel/trace/trace_sched_switch.c > b/kernel/trace/trace_sched_switch.c > index cb49f7279dc80..aabae7daaac91 100644 > --- a/kernel/trace/trace_sched_switch.c > +++ b/kernel/trace/trace_sched_switch.c > @@ -243,6 +243,8 @@ int trace_create_savedcmd(void) > int trace_save_cmdline(struct task_struct *tsk) > { > unsigned tpid, idx; > + /* so that map_pid_to_cmdline indexing is efficient */ > + BUILD_BUG_ON(!is_power_of_2(PID_MAX_DEFAULT)); Please move this to just above the test. And it doesn't need a comment, as it's obvious for why it needs to be a power of two when it's above the test. > > /* treat recording of idle task as a success */ > if (!tsk->pid) Like this: /* treat recording of idle task as a success */ if (!tsk->pid) return 1; + BUILD_BUG_ON(!is_power_of_2(PID_MAX_DEFAULT)); + tpid = tsk->pid & (PID_MAX_DEFAULT - 1); -- Steve
