From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
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 10:46:43 +0900 [thread overview]
Message-ID: <20161223014643.GA637@jagdpanzerIV.localdomain> (raw)
In-Reply-To: <20161222171012.GC14894@pathway.suse.cz>
On (12/22/16 18:10), Petr Mladek wrote:
...
> There are many callers. I think that such wrappers make sense.
> I would only like to keep naming scheme similar to the classic
> locks. I mean:
>
> printk_safe_enter_irq()
> printk_safe_exit_irq()
>
> printk_safe_enter_irqsave(flags)
> printk_safe_exit_irqrestore(flags)
sure.
> and
>
> logbuf_lock_irq()
> logbuf_unlock_irq()
>
> logbuf_lock_irqsave(flags)
> logbuf_lock_irqrestore(flags)
ok.
> I actually like this change. It makes it clear that the operation
> has a side effect (disables/enables irq) which was not visible
> from the original name.
agree.
> Well, I wonder how many times we need to call printk_save_enter/exit
> standalone (ouside these macros).
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".
> The question is if we really need all the variants of
> printk_safe_enter()/exit(). Alternative solution would be
> to handle only the printk_context in pritnk_safe_enter()
> and make sure that it is called with IRQs disabled.
> I mean to define only __printk_safe_enter()/exit()
> and do:
>
> #define logbuf_lock_irqsave(flags) \
> do { \
> local_irq_save(flags) \
> __printk_safe_enter(); \
> raw_spin_lock(&logbuf_lock); \
> } while (0)
won't do the trick for console sem spin_lock.
[..]
> 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.
-ss
next prev parent reply other threads:[~2016-12-23 1:46 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 [this message]
2016-12-23 9:53 ` Petr Mladek
2016-12-21 14:36 ` [PATCHv6 7/7] printk: remove zap_locks() function Sergey Senozhatsky
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