linux-kernel - Re: [PATCH] twist: allow converting pr_devel()/pr_debug() into printk(KERN

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Date:   Mon, 25 May 2020 14:03:48 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Ondrej Mosnacek <omosnace@...hat.com>,
        Joe Perches <joe@...ches.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] twist: allow converting pr_devel()/pr_debug() into
 printk(KERN_DEBUG)

On 2020/05/25 4:18, Ondrej Mosnacek wrote:
> I'm also not sure if this is really worth it... It would help localize
> the bug in this specific case, but there is nothing systematic about
> it. Are there that many debug print statements that dereference
> pointers that are later passed to functions, but not dereferenced
> otherwise? Maybe yes, but it seems to be quite an optimistic
> assumption... I don't consider it such a big problem that a bug in
> function X only manifests itself deeper in the callchain. There will
> always be such bugs, no matter how many moles you whack.

There are about 1400 pr_debug() callers. About 1000 pr_debug() callers seem
to pass plain '%p' (which is now likely useless for debugging purpose due to
default ptr_to_id() conversion inside pointer()), and about 400 pr_debug()
callers seem to pass '%p[a-zA-Z]' (which does some kind of dereference inside
pointer()). Thus, we might find some bugs by evaluating '%p[a-zA-Z]'.

On Sun, May 24, 2020 at 7:38 PM Joe Perches <joe@...ches.com> wrote:
> While I think this is rather unnecessary,
> what about dev_dbg/netdev_dbg/netif_dbg et al ?

Maybe a good idea, for there are about 24000 *dev_dbg() callers, and
479 callers pass '%p[a-zA-Z]'. But we can defer to another patch, in
case this patch finds crashes before fuzz testing process starts.