From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Petr Mladek <pmladek@suse.com>
Cc: "Tobin C . Harding" <me@tobin.cc>,
linux@rasmusvillemoes.dk, Joe Perches <joe@perches.com>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.cz>
Subject: Re: [PATCH v2 8/9] lib/vsprintf: Remove useless NULL checks
Date: Wed, 28 Feb 2018 12:42:24 +0200 [thread overview]
Message-ID: <1519814544.10722.266.camel@linux.intel.com> (raw)
In-Reply-To: <20180228100437.o4juwxbzomkqjvjx@pathway.suse.cz>
On Wed, 2018-02-28 at 11:04 +0100, Petr Mladek wrote:
> On Tue 2018-02-27 19:35:50, Andy Shevchenko wrote:
> > On Tue, 2018-02-27 at 16:50 +0100, Petr Mladek wrote:
> > > On Fri 2018-02-16 23:07:10, Andy Shevchenko wrote:
> > > > The pointer can't be NULL since it's first what has been done in
> > > > the
> > > > pointer().
> > > >
> > > > Remove useless checks.
> > > >
> > > > Note we leave check for !CONFIG_HAVE_CLK to make compiler
> > > > to optimize code away when possible.
> > > >
> I see
> https://lkml.kernel.org/r/1500546142.29303.133.camel@linux.intel.com
> There you suggested to move this check into pointer(). But I do not
> see any agreement on this.
> I am not aware of any. But this patch will make fixing such locations
> more complicated. The kernel would crash and might not show any
> message.
> Is this really what we want?
I never see such, so, I don't know what we want here.
> Note that it will most likely crash in vprintk_emit() on the line
>
> text_len = vscnprintf(text, sizeof(textbuf), fmt, args);
>
> It will be with logbug_lock() taken. The nested printk() messages
> will be stored in per-CPU buffer thanks to printk_safe code.
Yeah, that's bad.
> It would be easier if printk() was able to show the message
> when hitting this place.
>
> I did some archaeology. The first check for PAGE_SIZE was added
> by the pre-git commit:
>
> commit 8bcb3ba1dec5749a7f1eed570cb69a20c2e4bd41
> Author: Andrew Morton <akpm@osdl.org>
> Date: Tue Oct 21 18:22:28 2003 -0700
>
> [PATCH] make printk more robust with "null" pointers
>
> Expand printk's traditional handling of null pointers so that
> anything in the
> first page is considered a null pointer.
>
> This gives us better behaviour when someone (acpi..) accidentally
> prints a
> string which is embedded in a struct, the pointer to which is
> null.
>
>
> IMHO, it would make sense to hanve this check also pointers that are
> being deferred.
Send a patch to discuss!
> > > To be honest, I do not feel experienced enough to decide
> > > about the preferred behavior. On one hand, it is bad when
> > > printk() would crash the kernel. On the other hand, hiding wide
> > > range of values under "(null)" string might confuse people.
> > > Would it make sense to survive and write different strings for
> > > difference intervals? For example?
> > >
> > > "(null)" for ptr == 0
> > > "(null-16)" for ptr > 0 && ptr <= 16
> > > "(null-pg)" for prt > 16 && ptr <= PAGE_SIZE
> > >
> > > In each case, this patch changes the behavior and it should
> > > be documented in the commit message.
> >
> > Personally I strongly disagree with blowing code up in such places
> > for
> > little or none benefit.
>
> I do not have strong opinion here. I could imagine that this might
> save a day to some people. But I have never encountered such a bug
> myself.
>
> To make it clear. Your clean up work makes sense. I just want to point
> out that this patch is not as innocent as the commit message suggest.
> Also I think that it goes in the wrong direction regarding the
> ability to show useful information in a buggy situation.
Send a patch to discuss!
I consider silence as not preventing me doing my way. It seems you are
the first one who looks into this closer than the other(s) [Rasmus].
--
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy
next prev parent reply other threads:[~2018-02-28 10:42 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-16 21:07 [PATCH v2 1/9] lib/test_printf: Mark big constant with ULL Andy Shevchenko
2018-02-16 21:07 ` [PATCH v2 2/9] lib/vsprintf: Make dec_spec global Andy Shevchenko
2018-04-11 9:44 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 3/9] lib/vsprintf: Make strspec global Andy Shevchenko
2018-04-11 9:44 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 4/9] lib/vsprintf: Make flag_spec global Andy Shevchenko
2018-04-11 9:45 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 5/9] lib/vsprintf: Move pointer_string() upper Andy Shevchenko
2018-04-11 9:45 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 6/9] lib/vsprintf: Deduplicate pointer_string() Andy Shevchenko
2018-04-11 9:46 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 7/9] lib/vsprintf: Replace space with '_' before crng is ready Andy Shevchenko
2018-02-20 2:57 ` [此邮件可能存在风险] " Yang, Shunyong
2018-04-11 9:47 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 8/9] lib/vsprintf: Remove useless NULL checks Andy Shevchenko
2018-02-27 15:50 ` Petr Mladek
2018-02-27 17:35 ` Andy Shevchenko
2018-02-28 10:04 ` Petr Mladek
2018-02-28 10:42 ` Andy Shevchenko [this message]
2018-03-02 12:51 ` Petr Mladek
2018-03-02 12:53 ` [PATCH] vsprintf: Make "null" pointer dereference more robust Petr Mladek
2018-03-02 14:17 ` Andy Shevchenko
2018-03-05 14:53 ` Petr Mladek
2018-03-29 15:13 ` Petr Mladek
2018-03-29 16:11 ` Joe Perches
2018-03-05 15:16 ` Rasmus Villemoes
2018-03-05 15:25 ` Andy Shevchenko
2018-03-06 9:25 ` Petr Mladek
2018-03-06 9:56 ` Andy Shevchenko
2018-03-07 15:52 ` Petr Mladek
2018-03-07 18:18 ` Andy Shevchenko
2018-03-07 18:34 ` Linus Torvalds
2018-03-08 14:18 ` Petr Mladek
2018-03-08 16:45 ` Linus Torvalds
2018-03-08 17:26 ` Linus Torvalds
2018-03-09 15:01 ` Petr Mladek
2018-03-09 19:05 ` Linus Torvalds
2018-03-14 14:09 ` [PATCH v3] vsprintf: Prevent crash when dereferencing invalid pointers Petr Mladek
2018-03-14 22:12 ` Rasmus Villemoes
2018-03-15 15:07 ` Petr Mladek
2018-03-15 17:07 ` Steven Rostedt
2018-03-15 17:06 ` Steven Rostedt
2018-03-15 0:57 ` Sergey Senozhatsky
2018-03-15 7:58 ` Sergey Senozhatsky
2018-03-15 8:03 ` Sergey Senozhatsky
2018-03-15 17:01 ` Steven Rostedt
2018-03-16 1:18 ` Sergey Senozhatsky
2018-03-16 1:35 ` Linus Torvalds
2018-03-16 5:53 ` Sergey Senozhatsky
2018-03-16 8:55 ` Petr Mladek
2018-03-16 14:32 ` Steven Rostedt
2018-03-17 1:29 ` Sergey Senozhatsky
2018-03-15 13:07 ` Andy Shevchenko
2018-03-15 13:09 ` Andy Shevchenko
2018-03-15 15:26 ` Petr Mladek
2018-03-16 18:19 ` Andy Shevchenko
2018-03-29 14:53 ` Petr Mladek
2018-04-02 14:15 ` Andy Shevchenko
2018-04-03 1:12 ` Sergey Senozhatsky
2018-04-03 11:52 ` Petr Mladek
2018-04-03 11:56 ` Andy Shevchenko
2018-04-03 13:57 ` Sergey Senozhatsky
2018-04-03 11:46 ` Petr Mladek
2018-04-03 11:54 ` Andy Shevchenko
2018-04-03 13:13 ` Petr Mladek
2018-04-03 13:40 ` Andy Shevchenko
2018-04-03 14:50 ` Petr Mladek
2018-03-15 14:48 ` kbuild test robot
2018-03-15 20:26 ` kbuild test robot
2018-03-06 18:11 ` [PATCH 1/2] vsprintf: distinguish between (null), (err) and (invalid) pointer derefs Adam Borowski
2018-03-06 18:11 ` [PATCH 2/2] vsprintf: don't dereference pointers to the first or last page Adam Borowski
2018-03-07 13:22 ` Andy Shevchenko
2018-03-07 13:17 ` [PATCH 1/2] vsprintf: distinguish between (null), (err) and (invalid) pointer derefs Andy Shevchenko
2018-03-07 13:42 ` Adam Borowski
2018-03-07 13:29 ` Andy Shevchenko
2018-03-02 14:15 ` [PATCH v2 8/9] lib/vsprintf: Remove useless NULL checks Andy Shevchenko
2018-03-05 14:57 ` Petr Mladek
2018-02-28 10:44 ` Andy Shevchenko
2018-03-01 14:56 ` Andy Shevchenko
2018-02-16 21:07 ` [PATCH v2 9/9] lib/vsprintf: Mark expected switch fall-through Andy Shevchenko
2018-04-11 9:47 ` Petr Mladek
2018-02-18 12:58 ` [PATCH v2 1/9] lib/test_printf: Mark big constant with ULL Luc Van Oostenryck
2018-02-18 14:20 ` Andy Shevchenko
2018-02-19 15:24 ` Andy Shevchenko
2018-04-11 9:41 ` Petr Mladek
2018-02-18 21:52 ` Tobin C. Harding
2018-02-18 23:55 ` Andy Shevchenko
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