Re: [PATCH v11 01/19] dyndbg: add _DPRINTK_FLAGS_ENABLED

Vincent Whitchurch
2022-01-14T11:57:21Z

On Fri, Jan 07, 2022 at 06:29:24AM +0100, Jim Cromie wrote:
> #ifdef CONFIG_JUMP_LABEL
> - if (dp->flags & _DPRINTK_FLAGS_PRINT) {
> - if (!(modifiers->flags & _DPRINTK_FLAGS_PRINT))
> + if (dp->flags & _DPRINTK_FLAGS_ENABLED) {
> + if (!(modifiers->flags & _DPRINTK_FLAGS_ENABLED))
> static_branch_disable(&dp->key.dd_key_true);
> - } else if (modifiers->flags & _DPRINTK_FLAGS_PRINT)
> + } else if (modifiers->flags & _DPRINTK_FLAGS_ENABLED)
> static_branch_enable(&dp->key.dd_key_true);
> #endif
> dp->flags = newflags;
> --
> 2.33.1
>

I haven't tested it so I could be mistaken, but when
_DPRINTK_FLAGS_ENABLED gets two flags in the next patch, it looks like
this code still has the problem which I mentioned in
https://lore.kernel.org/lkml/20211209150910.GA23668@axis.com/?

| I noticed a bug inside the CONFIG_JUMP_LABEL handling (also present
| in the last version I posted) which should be fixed as part of the
| diff below (I've added a comment).
| [...]
| #ifdef CONFIG_JUMP_LABEL
| - if (dp->flags & _DPRINTK_FLAGS_PRINT) {
| - if (!(modifiers->flags & _DPRINTK_FLAGS_PRINT))
| + if (dp->flags & _DPRINTK_FLAGS_ENABLE) {
| + /*
| + * The newflags check is to ensure that the
| + * static branch doesn't get disabled in step
| + * 3:
| + *
| + * (1) +pf
| + * (2) +x
| + * (3) -pf
| + */
| + if (!(modifiers->flags & _DPRINTK_FLAGS_ENABLE) &&
| + !(newflags & _DPRINTK_FLAGS_ENABLE)) {
| static_branch_disable(&dp->key.dd_key_true);
| - } else if (modifiers->flags & _DPRINTK_FLAGS_PRINT)
| + }
| + } else if (modifiers->flags & _DPRINTK_FLAGS_ENABLE) {
| static_branch_enable(&dp->key.dd_key_true);
| + }
| #endif