From: Steven Rostedt <rostedt@goodmis.org>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Petr Mladek <pmladek@suse.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>,
Calvin Owens <calvinowens@fb.com>, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>,
Peter Hurley <peter@hurleysoftware.com>,
linux-kernel@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCHv7 3/8] printk: introduce per-cpu safe_print seq buffer
Date: Wed, 1 Feb 2017 10:52:13 -0500 [thread overview]
Message-ID: <20170201105213.351d1a01@gandalf.local.home> (raw)
In-Reply-To: <20161227141611.940-4-sergey.senozhatsky@gmail.com>
On Tue, 27 Dec 2016 23:16:06 +0900
Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:
> This patch extends the idea of NMI per-cpu buffers to regions
> that may cause recursive printk() calls and possible deadlocks.
> Namely, printk() can't handle printk calls from schedule code
> or printk() calls from lock debugging code (spin_dump() for instance);
> because those may be called with `sem->lock' already taken or any
> other `critical' locks (p->pi_lock, etc.). An example of deadlock
> can be
>
> vprintk_emit()
> console_unlock()
> up() << raw_spin_lock_irqsave(&sem->lock, flags);
> wake_up_process()
> try_to_wake_up()
> ttwu_queue()
> ttwu_activate()
> activate_task()
> enqueue_task()
> enqueue_task_fair()
> cfs_rq_of()
> task_of()
> WARN_ON_ONCE(!entity_is_task(se))
> vprintk_emit()
> console_trylock()
> down_trylock()
> raw_spin_lock_irqsave(&sem->lock, flags)
> ^^^^ deadlock
>
> and some other cases.
>
> Just like in NMI implementation, the solution uses a per-cpu
> `printk_func' pointer to 'redirect' printk() calls to a 'safe'
> callback, that store messages in a per-cpu buffer and flushes
> them back to logbuf buffer later.
>
> Usage example:
>
> printk()
> printk_safe_enter_irqsave(flags)
> //
> // any printk() call from here will endup in vprintk_safe(),
> // that stores messages in a special per-CPU buffer.
> //
> printk_safe_exit_irqrestore(flags)
>
> The 'redirection' mechanism, though, has been reworked, as suggested
> by Petr Mladek. Instead of using a per-cpu @print_func callback we now
> keep a per-cpu printk-context variable and call either default or nmi
> vprintk function depending on its value. printk_nmi_entrer/exit and
> printk_safe_enter/exit, thus, just set/celar corresponding bits in
> printk-context functions.
>
> The patch only adds printk_safe support, we don't use it yet.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
/me does the actual reviewed-by now :-p
Yes, I like this approach. I probably would have done it pretty much
the same way.
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
next prev parent reply other threads:[~2017-02-01 15:52 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-27 14:16 [PATCHv7 0/8] printk: use printk_safe to handle printk() recursive calls Sergey Senozhatsky
2016-12-27 14:16 ` [PATCHv7 1/8] printk: use vprintk_func in vprintk() Sergey Senozhatsky
2016-12-27 14:16 ` [PATCHv7 2/8] printk: rename nmi.c and exported api Sergey Senozhatsky
2017-01-04 13:07 ` Petr Mladek
2017-02-01 15:48 ` Steven Rostedt
2017-02-01 15:50 ` Steven Rostedt
2017-02-23 7:50 ` Geert Uytterhoeven
2017-02-23 8:02 ` Sergey Senozhatsky
2017-02-23 9:23 ` Geert Uytterhoeven
2016-12-27 14:16 ` [PATCHv7 3/8] printk: introduce per-cpu safe_print seq buffer Sergey Senozhatsky
2017-01-04 13:31 ` Petr Mladek
2017-01-05 1:01 ` Sergey Senozhatsky
2017-02-01 15:52 ` Steven Rostedt [this message]
2016-12-27 14:16 ` [PATCHv7 4/8] printk: always use deferred printk when flush printk_safe lines Sergey Senozhatsky
2017-02-01 16:06 ` Steven Rostedt
2017-02-02 6:05 ` Sergey Senozhatsky
2017-02-02 15:37 ` Petr Mladek
2017-02-02 15:52 ` Petr Mladek
2017-02-03 2:04 ` Sergey Senozhatsky
2017-02-03 11:18 ` Petr Mladek
2017-02-06 1:48 ` Sergey Senozhatsky
2017-02-06 2:08 ` Sergey Senozhatsky
2017-02-06 12:16 ` Petr Mladek
2017-02-06 13:27 ` Steven Rostedt
2017-02-06 16:42 ` Sergey Senozhatsky
2017-02-06 16:55 ` Steven Rostedt
2016-12-27 14:16 ` [PATCHv7 5/8] printk: report lost messages in printk safe/nmi contexts Sergey Senozhatsky
2017-01-04 14:46 ` Petr Mladek
2017-01-05 1:01 ` Sergey Senozhatsky
2017-02-01 16:37 ` Steven Rostedt
2017-02-02 2:02 ` Sergey Senozhatsky
2017-02-02 14:34 ` Steven Rostedt
2017-02-02 16:13 ` Petr Mladek
2017-02-03 1:57 ` Sergey Senozhatsky
2017-02-03 3:13 ` Steven Rostedt
2016-12-27 14:16 ` [PATCHv7 6/8] printk: use printk_safe buffers in printk Sergey Senozhatsky
2017-01-31 17:27 ` Ross Zwisler
2017-02-01 9:06 ` Jan Kara
2017-02-01 9:37 ` Peter Zijlstra
2017-02-01 15:39 ` Petr Mladek
2017-02-01 16:15 ` Peter Zijlstra
2017-02-01 16:41 ` Steven Rostedt
2017-02-02 2:11 ` Sergey Senozhatsky
2017-02-02 9:07 ` Peter Zijlstra
2017-02-02 10:03 ` Sergey Senozhatsky
2017-02-02 15:20 ` Petr Mladek
2017-02-03 2:45 ` Sergey Senozhatsky
2017-02-02 1:59 ` Sergey Senozhatsky
2017-02-01 17:04 ` Steven Rostedt
2017-02-02 2:13 ` Sergey Senozhatsky
2016-12-27 14:16 ` [PATCHv7 7/8] printk: remove zap_locks() function Sergey Senozhatsky
2016-12-27 14:16 ` [PATCHv7 8/8] printk: convert the rest to printk-safe Sergey Senozhatsky
2017-01-04 16:28 ` Petr Mladek
2017-01-05 1:00 ` Sergey Senozhatsky
2017-01-05 16:58 ` [PATCHv7 0/8] printk: use printk_safe to handle printk() recursive calls Petr Mladek
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