From: Steven Rostedt <rostedt@goodmis.org>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sysrq: Restore original console_loglevel when sysrq disabled
Date: Fri, 11 Jan 2019 11:24:09 -0500 [thread overview]
Message-ID: <20190111112409.6babfa2a@gandalf.local.home> (raw)
In-Reply-To: <20190111130729.GA31790@tigerII.localdomain>
On Fri, 11 Jan 2019 22:07:29 +0900
Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:
> On (01/11/19 13:45), Petr Mladek wrote:
> > The sysrq header line is printed with an increased loglevel
> > to provide users some positive feedback.
> >
> > The original loglevel is not restored when the sysrq operation
> > is disabled. This bug was introduced in 2.6.12 (pre-git-history)
> > by the commit ("Allow admin to enable only some of the Magic-Sysrq
> > functions").
>
>
> Good find, and the patch looks OK to me. A small comment below.
> FWIW,
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
>
>
> ---
>
> A side note (nitpick, etc.); it's Friday night in here, I'm enjoying
> my beer; so maybe I'm wrong about the whole thing.
>
>
> > @@ -553,6 +553,7 @@ void __handle_sysrq(int key, bool check_mask)
> > op_p->handler(key);
> > } else {
> > pr_cont("This sysrq operation is disabled.\n");
> > + console_loglevel = orig_log_level;
> > }
>
> This looks a bit racy.
>
> When we do
>
> printk("FOO\n");
> console_loglevel = XYZ;
>
> We don't have any real guarantees that printk("FOO\n") will print
> anything straight ahead. It is possible that console_sem is already
> locked and the owner is preempted, so by the time the console_sem
> owner picks up that FOO\n messages, console_loglevel is back to
> orig_log_level and suppress_message_printing() will just tell us
> to skip the message.
>
> Do we need pr_cont() there? Maybe we can just have a normal pr_err()
> which would always tell that "key" sysrq is disabled? (we also
> would need to change the error message a bit).
>
All this is for another patch and another discussion. This current
patch keeps with what is there and fixes a missing reset of
console_loglevel.
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
prev parent reply other threads:[~2019-01-11 16:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-11 12:45 [PATCH] sysrq: Restore original console_loglevel when sysrq disabled Petr Mladek
2019-01-11 13:07 ` Sergey Senozhatsky
2019-01-11 15:32 ` Petr Mladek
2019-01-14 5:36 ` Sergey Senozhatsky
2019-01-14 14:37 ` Petr Mladek
2019-01-11 16:24 ` Steven Rostedt [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190111112409.6babfa2a@gandalf.local.home \
--to=rostedt@goodmis.org \
--cc=gregkh@linuxfoundation.org \
--cc=jslaby@suse.com \
--cc=linux-kernel@vger.kernel.org \
--cc=pmladek@suse.com \
--cc=sergey.senozhatsky.work@gmail.com \
--cc=sergey.senozhatsky@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).