From: Petr Mladek <pmladek@suse.com>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
syzbot <syzbot+43e93968b964e369db0b@syzkaller.appspotmail.com>,
linux-kernel@vger.kernel.org, rostedt@goodmis.org,
syzkaller-bugs@googlegroups.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>,
linux-serial@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: possible deadlock in console_unlock
Date: Fri, 8 Jun 2018 10:18:55 +0200 [thread overview]
Message-ID: <20180608081855.ctqakvwmg27aydby@pathway.suse.cz> (raw)
In-Reply-To: <20180607140100.GA398@tigerII.localdomain>
On Thu 2018-06-07 23:01:00, Sergey Senozhatsky wrote:
> On (06/07/18 13:00), Petr Mladek wrote:
> > > Another way could be - switch to printk_safe mode around that
> > > kmalloc():
> > >
> > > __printk_safe_enter();
> > > kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
> > > __printk_safe_exit();
> > >
> > > Or, may be, we even can switch to printk_safe mode every time we grab
> > > tty_port lock.
> >
> > > Perhaps something like this should be done for uart_port->lock
> > > as well. Because, technically, we can have the following
> >
> > Yeah, we would need this basically around any lock that can be taken
> > from console write() callbacks. Well, this would be needed even
> > around locks that might be in a chain with a lock used in these
> > callbacks (as shown by this report).
>
> Yep. So the plan for now is to wrap the tty_port->lock. Pretty much
> an automatic conversion.
>
> Then to convert [may be some for now on] uart_port->lock. Once again,
> pretty much can be done a script.
>
> Afterwards just sit down and be humbl^W^W wait for new reports. Then
> move those newly discovered unsafe locks under printk_safe context.
>
> Basically, the same macros as we use for logbuf lock in printk.c
>
> A bit of a lazy approach. Can't think of anything better.
Same here.
> I think it's finally the time to start dealing with these
> "external" locks, it's been a while.
>
> > BTW: printk_safe context might be too strict. In fact,
> > printk_deferred() would be enough. We might think about
> > introducing also printk_deferred context.
>
> Could be.
> The good thing about printk_safe is that printk_safe sections can nest.
> I suspect there might be locks/printk_safe sections nesting at some
> point. In any case, switching to a new flavor of printk_safe will be
> pretty easy - just replace printk_safe_enter() with printk_foo_enter()
> and the same for printk_save_exit().
We could allow nesting. It is just a matter of how many bits we
reserve for it in printk_context variable.
In each case, I would like to keep the printk_safe context usage
at minimum. It has its own problems caused by limited per-cpu buffers
and the need to flush them. It is basically needed only to prevent
deadlocks related to logbuf_lock.
Best Regards,
Petr
next prev parent reply other threads:[~2018-06-08 8:19 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-06 13:17 possible deadlock in console_unlock syzbot
2018-06-07 4:44 ` syzbot
2018-06-07 5:10 ` Sergey Senozhatsky
2018-06-07 11:00 ` Petr Mladek
2018-06-07 11:40 ` Tetsuo Handa
2018-06-07 14:03 ` Sergey Senozhatsky
2018-06-07 14:01 ` Sergey Senozhatsky
2018-06-08 8:18 ` Petr Mladek [this message]
2018-06-15 8:38 ` Sergey Senozhatsky
2018-06-19 8:04 ` Petr Mladek
2018-06-19 8:08 ` Sergey Senozhatsky
2019-02-20 10:52 ` Tetsuo Handa
2019-11-25 2:41 ` syzbot
2019-02-16 6:36 Yao HongBo
2019-02-16 7:21 ` Sergey Senozhatsky
2019-02-16 7:46 ` Sergey Senozhatsky
2019-02-16 7:59 ` Yao HongBo
2019-02-18 5:46 ` Sergey Senozhatsky
2019-02-18 12:09 ` Yao HongBo
2019-02-18 14:07 ` Yao HongBo
2019-02-19 1:32 ` Sergey Senozhatsky
2019-02-19 2:48 ` Yao HongBo
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