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From: Petr Mladek <pmladek@suse.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>,
	Calvin Owens <calvinowens@fb.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	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@gmail.com>
Subject: Re: [PATCHv6 6/7] printk: use printk_safe buffers in printk
Date: Fri, 23 Dec 2016 10:53:41 +0100	[thread overview]
Message-ID: <20161223095341.GA2541@linux.suse> (raw)
In-Reply-To: <20161223014643.GA637@jagdpanzerIV.localdomain>

On Fri 2016-12-23 10:46:43, Sergey Senozhatsky wrote:
> not every switch to printk_safe is "dictated" by logbuf_lock.
> down_trylock_console_sem(), for instance, takes semaphore spin_lock
> which already may be locked on the same CPU (*), so we need to be
> in safe mode:
> 
> vprintk_emit()
>  down_trylock()
>   raw_spin_lock_irqsave(&sem->lock, flags);
>   ...
>   raw_spin_unlock_irqrestore(&sem->lock, flags);
>    spin_dump()
>     printk()
>      vprintk_emit()
>       down_trylock()
>        raw_spin_lock_irqsave(&sem->lock, flags)   << deadlock
> 
> 
> and so on. IOW, "printk_save_enter()" != "logbuf_lock is acquired".

You are right. It seems that the

printk_safe_enter_irq()
printk_safe_exit_irq()

printk_safe_enter_irqsave(flags)
printk_safe_exit_irqrestore(flags)

variants make sense and we will need them together with
the logbuf_lock_*() stuff.

> [..]
> > PS: I still think if we could come with a better name than
> > printk_safe() but I cannot find one.
> 
> well, not that I'm the fan of printk_safe name, but can't think
> of anything better. we make printk calls safe (deadlock safe) in
> places where previously it was unsafe... quick-&-dirty name that
> is implementation-specific -- printk_percpu_enter/exit, or
> printk_pcpu_enter/exit... dunno.

OK, let's stay with printk_safe :-)

Best Reagards,
Petr

  reply	other threads:[~2016-12-23  9:53 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-21 14:35 [PATCHv6 0/7] printk: use printk_safe to handle printk() recursive calls Sergey Senozhatsky
2016-12-21 14:35 ` [PATCHv6 1/7] printk: use vprintk_func in vprintk() Sergey Senozhatsky
2016-12-21 14:36 ` [PATCHv6 2/7] printk: rename nmi.c and exported api Sergey Senozhatsky
2016-12-21 19:45   ` Linus Torvalds
2016-12-22  1:17     ` Sergey Senozhatsky
2016-12-21 14:36 ` [PATCHv6 3/7] printk: introduce per-cpu safe_print seq buffer Sergey Senozhatsky
2016-12-22  0:53   ` kbuild test robot
2016-12-22  1:18     ` Sergey Senozhatsky
2016-12-22 16:36       ` Petr Mladek
2016-12-21 14:36 ` [PATCHv6 4/7] printk: always use deferred printk when flush printk_safe lines Sergey Senozhatsky
2016-12-21 14:36 ` [PATCHv6 5/7] printk: report lost messages in printk safe/nmi contexts Sergey Senozhatsky
2016-12-23 10:54   ` Petr Mladek
2016-12-23 15:08     ` Sergey Senozhatsky
2016-12-21 14:36 ` [PATCHv6 6/7] printk: use printk_safe buffers in printk Sergey Senozhatsky
2016-12-22  5:31   ` Sergey Senozhatsky
2016-12-22 17:10     ` Petr Mladek
2016-12-23  1:46       ` Sergey Senozhatsky
2016-12-23  9:53         ` Petr Mladek [this message]
2016-12-21 14:36 ` [PATCHv6 7/7] printk: remove zap_locks() function Sergey Senozhatsky

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