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
next prev parent 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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