Re: [PATCH v6 15/24] dyndbg: refactor param_set_dyndbg_classes and below

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] param_set_dyndbg_module_classes() fails to initialize debug queries for a newly probed module because it incorrectly uses the global class parameter state as the baseline (`old_bits`).
--

--- Patch [15]: [PATCH v6 15/24] dyndbg: refactor param_set_dyndbg_classes and below ---
commit 041ecc33e02248dbfd09801bededdf6047b80f6e
Author: Jim Cromie <jim.cromie@gmail.com>

dyndbg: refactor param_set_dyndbg_classes and below

This commit refactors the param_set_dyndbg_classes callchain to allow
module-specific settings by passing a modname parameter down to
ddebug_apply_class_bitmap and ddebug_exec_queries. It also adds a check
to announce bit changes only when they actually change.

> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> index ce42e03f1600a..0fc9cd14e2d20 100644
> --- a/lib/dynamic_debug.c
> +++ b/lib/dynamic_debug.c
[ ... ]
> @@ -682,8 +692,8 @@ int param_set_dyndbg_classes(const char *instr, const struct kernel_param *kp)
>  				KP_NAME(kp), inrep, CLASSMAP_BITMASK(map->length));
>  			inrep &= CLASSMAP_BITMASK(map->length);
>  		}
> -		v2pr_info("bits:%lx > %s\n", inrep, KP_NAME(kp));
> -		totct += ddebug_apply_class_bitmap(dcp, &inrep, dcp->bits);
> +		v2pr_info("bits:0x%lx > %s.%s\n", inrep, mod_name ?: "*", KP_NAME(kp));
> +		totct += ddebug_apply_class_bitmap(dcp, &inrep, dcp->bits, mod_name);
>  		*dcp->bits = inrep;
>  		break;
>  	case DD_CLASS_TYPE_LEVEL_NUM:
> @@ -696,7 +706,7 @@ int param_set_dyndbg_classes(const char *instr, const struct kernel_param *kp)
>  		old_bits = CLASSMAP_BITMASK(*dcp->lvl);
>  		new_bits = CLASSMAP_BITMASK(inrep);
>  		v2pr_info("lvl:%ld bits:0x%lx > %s\n", inrep, new_bits, KP_NAME(kp));
> -		totct += ddebug_apply_class_bitmap(dcp, &new_bits, &old_bits);
> +		totct += ddebug_apply_class_bitmap(dcp, &new_bits, &old_bits, mod_name);

[Severity: Medium]
Does this skip enabling debug queries for newly probed modules if the global
state already has those bits set?

When param_set_dyndbg_module_classes() is called for a newly probed module
(mod_name != NULL), it passes the global class parameter state as the old
state (dcp->bits and old_bits respectively) instead of 0.

If a global parameter was previously set (e.g., drm.debug=2), those bits are
already present in the global state. The optimization loop in
ddebug_apply_class_bitmap() checks this:

lib/dynamic_debug.c:ddebug_apply_class_bitmap() {
    ...
    for (bi = 0; bi < map->length; bi++) {
        if (test_bit(bi, new_bits) == test_bit(bi, old_bits))
            continue;
    ...
}

Because the new module's target state matches the global state, it skips
executing the queries, even though the newly loaded module actually starts
with a default state of 0.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260707-dd-maint-2-v6-0-381f3edb0045@gmail.com?part=15