linux-kernel - Re: [PATCH v2] PM: fix dynamic debug within pm_pr

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Date:   Sat, 19 Mar 2022 01:54:09 +0000
From:   David Cohen <dacohen@...me>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] PM: fix dynamic debug within pm_pr_debug()

On Thu, Mar 17, 2022 at 02:45:11PM +0100, Rafael J. Wysocki wrote:
> On Sat, Mar 12, 2022 at 5:37 AM David Cohen <dacohen@...me> wrote:
> >
> > Currently, pm_pr_debug() and pm_deferred_pr_debug() use __pm_pr_debug()
> > to filter pm debug messages based on pm_debug_messages_on flag.
> > According to __pm_pr_debug() implementation, pm_deferred_pr_debug()
> > indirectly calls printk_deferred() within __pm_pr_debug() which doesn't
> > support dynamic debug, but pm_pr_debug() indirectly calls pr_debug()
>
> I'm not sure what you mean by pm_pr_debug().  There's no such thing in
> the kernel tree.
>
> Assuming that it means pm_pr_dbg(), it doesn't call pr_debug():

Yeah, I apologize for the typo. I meant pm_pr_dbg(). I can fix that if
you're ok with the patch as per comments below.

>
> #define pm_pr_dbg(fmt, ...) __pm_pr_dbg(false, fmt, ##__VA_ARGS__)
>
> and
>
> void __pm_pr_dbg(bool defer, const char *fmt, ...)
> {
> ...
>         if (defer)
>                printk_deferred(KERN_DEBUG "PM: %pV", &vaf);
>         else
>                printk(KERN_DEBUG "PM: %pV", &vaf);
>
> And as I said printk(KERN_DEBUG ...) is not equivalent to
> pr_debug(...), because it is not dynamic printk().

The problem is not about __pm_pr_dbg() calling printk(). The problem is
the pm files that used to call pr_debug() were modified to call
pm_pr_dbg() in order to be behing the pm_debug_messages_on flag, as per
this commit:
8d8b2441db96 PM / sleep: Do not print debug messages by default

That's the moment dynamic debug was no longer available for kernel pm files.

>
> pm_pr_dbg() is not dynamic printk() on purpose, so they both can be
> controlled independently.

The current solution is all or nothing (using pm_debug_messages_on). The
patch I'm sending is making dynamic debug available on the kernel pm
files, while still allowing the pm_debug_messages_on flag to work
independently.

Regards, David