On Mon, Jul 18, 2022 at 12:28:35PM -0700, Yury Norov wrote:
> smp_call_function_many_cond() is often passed with cpu_online_mask.
> If this is the case, we can use num_online_cpus(), which is O(1)
> instead of cpumask_{first,next}(), which is O(N).
>
> It can be optimized further: if cpu_online_mask has 0 or single bit
> set (depending on cpu_online(this_cpu), we can return result without
> AND'ing with user's mask.
> Caught with CONFIG_DEBUG_BITMAP:
> [ 7.830337] Call trace:
> [ 7.830397] __bitmap_check_params+0x1d8/0x260
> [ 7.830499] smp_call_function_many_cond+0x1e8/0x45c
> [ 7.830607] kick_all_cpus_sync+0x44/0x80
> [ 7.830698] bpf_int_jit_compile+0x34c/0x5cc
> [ 7.830796] bpf_prog_select_runtime+0x118/0x190
> [ 7.830900] bpf_prepare_filter+0x3dc/0x51c
> [ 7.830995] __get_filter+0xd4/0x170
> [ 7.831145] sk_attach_filter+0x18/0xb0
> [ 7.831236] sock_setsockopt+0x5b0/0x1214
> [ 7.831330] __sys_setsockopt+0x144/0x170
> [ 7.831431] __arm64_sys_setsockopt+0x2c/0x40
> [ 7.831541] invoke_syscall+0x48/0x114
> [ 7.831634] el0_svc_common.constprop.0+0x44/0xfc
> [ 7.831745] do_el0_svc+0x30/0xc0
> [ 7.831825] el0_svc+0x2c/0x84
> [ 7.831899] el0t_64_sync_handler+0xbc/0x140
> [ 7.831999] el0t_64_sync+0x18c/0x190
> [ 7.832086] ---[ end trace 0000000000000000 ]---
> [ 7.832375] b1: ffff24d1ffd98a48
> [ 7.832385] b2: ffffa65533a29a38
> [ 7.832393] b3: ffffa65533a29a38
> [ 7.832400] nbits: 256
> [ 7.832407] start: 0
> [ 7.832412] off: 0
> [ 7.832418] smp: Bitmap: parameters check failed
> [ 7.832432] smp: include/linux/bitmap.h [363]: bitmap_and
Documentation specifically says:
https://www.kernel.org/doc/html/latest/process/submitting-patches.html#backtraces-in-commit-mesages
...
> + default:
> + if (mask == cpu_online_mask)
> + return true;
Instead, put (missed) break; here and do "default" case together below.
> + cpu = cpumask_first_and(mask, cpu_online_mask);
> + if (cpu == this_cpu)
> + cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
> +
> + return cpu < nr_cpu_ids;
...
> + run_remote = __need_remote_exec(mask, this_cpu);
>
Now you may remove this blank line.
> if (run_remote) {
--
With Best Regards,
Andy Shevchenko
