From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [GIT PULL] printk for 4.13
Date: Thu, 6 Jul 2017 09:53:28 +0900 [thread overview]
Message-ID: <20170706005328.GB7195@jagdpanzerIV.localdomain> (raw)
In-Reply-To: <20170706004404.GA7195@jagdpanzerIV.localdomain>
On (07/06/17 09:44), Sergey Senozhatsky wrote:
> > No, this is entirely buggered.
> >
> > You can't just do
> >
> > raw_spin_is_locked(&logbuf_lock)
> >
> > to test whether you can get the logbuf_lock and then call vprintk_default().
> >
> > It's not just about deadlock avoidance, the code will call things like
> > down_trylock() on the console semaphore, and that operation is
> > fundamentally not NMI-safe. The semaphore count is literally protected
> > by a irq-safe (BUT NOT NMI-SAFE!) semaphore spinlock.
> >
> > So now you can instead deadlock just on the internal console semaphore
> > spinlock (ie somebody is doing "console_lock()", NMI comes in, *BOOM*.
>
> you are right. but
>
just in case if my previous email was too hard to follow, may be the
link below will explain it in a less broken language. (I'm sorry, I'm
on medication now and didn't have enough coffee yet.)
https://marc.info/?l=linux-kernel&m=149265908228203&w=2
-ss
next prev parent reply other threads:[~2017-07-06 0:53 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-03 14:24 [GIT PULL] printk for 4.13 Petr Mladek
2017-07-05 18:23 ` Linus Torvalds
2017-07-06 0:44 ` Sergey Senozhatsky
2017-07-06 0:53 ` Sergey Senozhatsky [this message]
2017-07-06 1:15 ` Linus Torvalds
2017-07-06 1:18 ` Sergey Senozhatsky
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