From: Petr Mladek <pmladek@suse.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
Daniel Wang <wonderfly@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
Jiri Slaby <jslaby@suse.com>, Peter Feiner <pfeiner@google.com>,
linux-serial@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [RFC][PATCHv2 2/4] printk: move printk_safe macros to printk header
Date: Tue, 16 Oct 2018 13:40:06 +0200 [thread overview]
Message-ID: <20181016114006.6q5atyaitapcwbud@pathway.suse.cz> (raw)
In-Reply-To: <20181016072719.GB4030@hirez.programming.kicks-ass.net>
On Tue 2018-10-16 09:27:19, Peter Zijlstra wrote:
> On Tue, Oct 16, 2018 at 02:04:26PM +0900, Sergey Senozhatsky wrote:
> > Make printk_safe_enter_irqsave()/etc macros available to the
> > rest of the kernel.
> >
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > ---
> > include/linux/printk.h | 40 +++++++++++++++++++++++++++++++++++++
> > kernel/printk/internal.h | 37 ----------------------------------
> > kernel/printk/printk_safe.c | 6 ++++--
> > 3 files changed, 44 insertions(+), 39 deletions(-)
> >
> > diff --git a/include/linux/printk.h b/include/linux/printk.h
> > index cf3eccfe1543..75f99441fd54 100644
> > --- a/include/linux/printk.h
> > +++ b/include/linux/printk.h
> > @@ -157,6 +157,46 @@ static inline void printk_nmi_direct_enter(void) { }
> > static inline void printk_nmi_direct_exit(void) { }
> > #endif /* PRINTK_NMI */
> >
> > +#ifdef CONFIG_PRINTK
> > +extern void printk_safe_enter(void);
> > +extern void printk_safe_exit(void);
> > +
> > +#define printk_safe_enter_irqsave(flags) \
> > + do { \
> > + local_irq_save(flags); \
> > + printk_safe_enter(); \
> > + } while (0)
> > +
> > +#define printk_safe_exit_irqrestore(flags) \
> > + do { \
> > + printk_safe_exit(); \
> > + local_irq_restore(flags); \
> > + } while (0)
> > +
> > +#define printk_safe_enter_irq() \
> > + do { \
> > + local_irq_disable(); \
> > + printk_safe_enter(); \
> > + } while (0)
> > +
> > +#define printk_safe_exit_irq() \
> > + do { \
> > + printk_safe_exit(); \
> > + local_irq_enable(); \
> > + } while (0)
>
> So I really _really_ hate all this. Utterly detest it.
>
> That whole magic 'safe' printk buffer crap is just that crap.
>
> Instead of this tinkering around the edges, why don't you make the main
> logbuf a lockless ringbuffer and then delegate the actual printing of
> that buffer to a kthread, except for earlycon, which can do synchronous
> output.
In fact, there is no problem with printk log buffer. This patchset
tries to avoid deadlock caused by console-specific locks
used by console->write() methods.
By other words, we neither need printk_safe or lockless log buffer
to fix this prolem. Instead, we need either printk_deferred context
or lockless consoles.
Best Regards,
Petr
next prev parent reply other threads:[~2018-10-16 11:40 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-16 5:04 [RFC][PATCHv2 0/4] less deadlock prone serial consoles Sergey Senozhatsky
2018-10-16 5:04 ` [RFC][PATCHv2 1/4] panic: avoid deadlocks in re-entrant console drivers Sergey Senozhatsky
2018-10-17 4:48 ` Sergey Senozhatsky
2018-10-23 11:07 ` Petr Mladek
2018-10-23 11:54 ` Sergey Senozhatsky
2018-10-23 12:04 ` Sergey Senozhatsky
2018-10-23 12:12 ` Sergey Senozhatsky
2018-10-25 9:06 ` Petr Mladek
2018-10-25 9:31 ` Sergey Senozhatsky
2018-10-25 8:29 ` Petr Mladek
2018-10-25 9:05 ` Sergey Senozhatsky
2018-10-25 10:10 ` [PATCHv3] " Sergey Senozhatsky
2018-10-25 10:51 ` kbuild test robot
2018-10-25 11:56 ` Sergey Senozhatsky
2018-10-31 12:27 ` Petr Mladek
2018-11-01 1:48 ` Sergey Senozhatsky
2018-11-01 8:08 ` Petr Mladek
2018-11-22 13:12 ` Petr Mladek
2018-12-12 0:53 ` Daniel Wang
2018-12-12 5:23 ` Sergey Senozhatsky
2018-12-12 5:59 ` Daniel Wang
2018-12-12 6:06 ` Sergey Senozhatsky
2018-12-12 6:09 ` Daniel Wang
2018-10-16 5:04 ` [RFC][PATCHv2 2/4] printk: move printk_safe macros to printk header Sergey Senozhatsky
2018-10-16 7:27 ` Peter Zijlstra
2018-10-16 11:40 ` Petr Mladek [this message]
2018-10-16 12:17 ` Peter Zijlstra
2018-10-17 10:50 ` Petr Mladek
2018-10-17 14:00 ` Peter Zijlstra
2018-10-22 14:30 ` Petr Mladek
2018-10-16 12:27 ` Sergey Senozhatsky
2018-10-16 12:38 ` Peter Zijlstra
2018-10-16 12:54 ` Peter Zijlstra
2018-10-16 14:21 ` Peter Zijlstra
2018-10-17 4:32 ` Sergey Senozhatsky
2018-10-17 7:57 ` Peter Zijlstra
2018-10-17 13:36 ` Sergey Senozhatsky
2018-10-23 6:25 ` Sergey Senozhatsky
2018-10-16 5:04 ` [RFC][PATCHv2 3/4] serial: introduce uart_port locking helpers Sergey Senozhatsky
2018-12-08 3:12 ` Sergey Senozhatsky
2018-12-12 11:08 ` Greg Kroah-Hartman
2018-10-16 5:04 ` [RFC][PATCHv2 4/4] tty: 8250: switch to " Sergey Senozhatsky
2018-10-16 7:23 ` [RFC][PATCHv2 0/4] less deadlock prone serial consoles Peter Zijlstra
2018-10-16 8:12 ` Sergey Senozhatsky
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