linux-kernel - Re: [PATCH v11 01/19] dyndbg: add _DPRINTK_FLAGS

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Message-ID: <CAJfuBxw1scH7xS7-RfxZ369wVQ8umP+0MHqz1U_3cW-BLPsDkg@mail.gmail.com>
Date:   Mon, 17 Jan 2022 15:33:33 -0700
From:   jim.cromie@...il.com
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     "jbaron@...mai.com" <jbaron@...mai.com>,
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Subject: Re: [PATCH v11 01/19] dyndbg: add _DPRINTK_FLAGS_ENABLED

On Fri, Jan 14, 2022 at 4:57 AM Vincent Whitchurch
<vincent.whitchurch@...s.com> wrote:
>
> 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/?
>

Yes, thanks for noticing.  I missed that detail.
Apriori, I dont know why bit-and of bit-or'd flags doesnt cover it,
but I will take a careful look.

> | 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