From: Feng Tang <feng.tang@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>,
Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>,
Borislav Petkov <bp@suse.de>,
ying.huang@intel.com
Subject: Re: [PATCH v2] panic: add an option to replay all the printk message in buffer
Date: Wed, 17 Apr 2019 14:48:44 +0800 [thread overview]
Message-ID: <20190417064844.ppyqxcx2mgek5455@shbuild888> (raw)
In-Reply-To: <20190416211922.d3c9c6987f0b992da343be52@linux-foundation.org>
Hi Andrew,
On Tue, Apr 16, 2019 at 09:19:22PM -0700, Andrew Morton wrote:
> On Wed, 10 Apr 2019 23:37:18 +0800 Feng Tang <feng.tang@intel.com> wrote:
>
> > Currently on panic, kernel will lower the loglevel and print out
> > new printk msg only with console_flush_on_panic().
> >
> > Add an option for users to configure the "panic_print" to see
> > all dmesg in buffer, some of which they may have never seen due
> > to the loglevel setting, which will help debugging too.
> >
> > Thanks to Petr Mladek as somes codes come directly from the sample
> > code in his review comments.
>
> CONFIG_PRINTK=n:
>
> kernel/printk/printk.c: In function console_unlock:
> kernel/printk/printk.c:2419:11: warning: __builtin_memcpy writing 27 bytes into a region of size 0 overflows the destination [-Wstringop-overflow=]
> len += sprintf(text + len,
> ^~~~~~~~~~~~~~~~~~~
> "Replaying the entire log:\n");
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> because LOG_LINE_MAX=0 and PREFIX_MAX=0.
Thanks for catching this!
>
>
> Which is interesting. The pre-existing
>
> len = sprintf(text,
> "** %llu printk messages dropped **\n",
> log_first_seq - console_seq);
>
> in console_unlock() has the same issue, but the compiler doesn't seem
> to want to warn.
For this one, I did some check, and it should be related with the
conditional check
if (console_seq < log_first_seq) {
Both the console_seq and log_first_seq will not be touched by any code
when CONFIG_PRINTK=n, and compiler will simply skip the whole code block,
as "console_seq < log_first_seq" will never happen.
But code block following "if (console_replay)" will be compiled, that's
why these warning message will be shown.
>
> (Also, using sprintf() is a bit lame for the new message - could use
> strlcpy()).
>
> I'll drop the patch for now - we don't want that warning to come out.
> console_unlock() needs some fixing for the CONFIG_PRINTK=n case.
My instant thought would be put the console_unlcok() and similar funcs
under CONFIG_PRINTK protection, while adding nop functions in the "else"
segment.
But complexer question will be when CONFIG_PRINTK=n, how those console_xxx
functions should consider these to make compiled binary smaller (though it
rarely happens). would wait for Petr/Sergey/Steven's insights.
Thanks,
Feng
next prev parent reply other threads:[~2019-04-17 6:45 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-10 15:37 [PATCH v2] panic: add an option to replay all the printk message in buffer Feng Tang
2019-04-17 4:19 ` Andrew Morton
2019-04-17 6:48 ` Feng Tang [this message]
2019-04-17 9:18 ` Petr Mladek
2019-04-17 9:46 ` Sergey Senozhatsky
2019-04-17 10:50 ` Sergey Senozhatsky
2019-04-17 12:24 ` Petr Mladek
2019-04-17 15:18 ` Feng Tang
2019-04-18 0:00 ` Sergey Senozhatsky
2019-04-18 7:45 ` Petr Mladek
2019-04-18 9:00 ` Feng Tang
2019-04-18 11:01 ` Petr Mladek
2019-04-19 2:08 ` Feng Tang
2019-04-18 10:50 ` Sergey Senozhatsky
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