From: Petr Mladek <pmladek@suse.com>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: John Ogness <john.ogness@linutronix.de>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: consoles: was: [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog_lock
Date: Mon, 7 Dec 2020 10:50:02 +0100 [thread overview]
Message-ID: <X836yrIxyIp5y+Qq@alley> (raw)
In-Reply-To: <X8sPGfe2kWkAqsl1@jagdpanzerIV.localdomain>
On Sat 2020-12-05 13:39:53, Sergey Senozhatsky wrote:
> On (20/12/04 17:19), Petr Mladek wrote:
> [..]
> > > --- a/kernel/printk/printk.c
> > > +++ b/kernel/printk/printk.c
> > > @@ -2432,7 +2490,6 @@ void console_unlock(void)
> > > size_t len;
> > >
> > > printk_safe_enter_irqsave(flags);
> >
> > Why do we actually need to use the printk_safe context here?
> > There is not longer a risk of deadlock caused by logbuf_lock.
> > All other recursions should be prevented by console_trylock()
> > in printk().
>
> All semaphore functions, including down_trylock(), acquire
> semaphore spin_lock;
This has a very easy solution. The patch adds a code that counts
recursion level. We just must not call console_trylock() when
being inside a recursive printk.
printk_safe() has two functions:
1. It allows to store messages a lockless way. This is obsoleted
by the lockless ringbuffer.
2. It prevents calling consoles. We could move this check
into vprintk_store(). We already have there similar check
for printk_deferred().
> and then some call into the scheduler
> (or other kernel core functions) under semaphore's spin_lock.
> For instance
>
> up()
> raw_spin_lock_irqsave(&sem->lock)
> __up()
> wake_up_process()
> try_to_wake_up()
This problem is partly solved by printk_deferred(). In each
case, printk_safe() does not help here.
I still do _not_ see a reason to keep printk_safe()!
Best Regards,
Petr
next prev parent reply other threads:[~2020-12-07 9:51 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-01 20:53 [PATCH next v2 0/3] printk: remove logbuf_lock John Ogness
2020-12-01 20:53 ` [PATCH next v2 1/3] printk: inline log_output(),log_store() in vprintk_store() John Ogness
2020-12-03 15:57 ` Petr Mladek
2020-12-03 16:25 ` John Ogness
2020-12-04 6:13 ` Sergey Senozhatsky
2020-12-04 8:26 ` Petr Mladek
2020-12-01 20:53 ` [PATCH next v2 2/3] printk: change @clear_seq to atomic64_t John Ogness
2020-12-04 9:12 ` Petr Mladek
2020-12-06 20:23 ` John Ogness
2020-12-07 9:34 ` Peter Zijlstra
2020-12-07 10:03 ` John Ogness
2020-12-07 12:56 ` Peter Zijlstra
2020-12-07 12:56 ` Petr Mladek
2020-12-07 16:46 ` David Laight
2020-12-08 20:34 ` Sergey Senozhatsky
2020-12-08 22:30 ` John Ogness
2020-12-09 1:04 ` Sergey Senozhatsky
2020-12-09 8:16 ` Peter Zijlstra
2020-12-09 9:22 ` Sergey Senozhatsky
2020-12-09 10:46 ` Sergey Senozhatsky
2020-12-09 11:00 ` Peter Zijlstra
2020-12-09 11:28 ` Sergey Senozhatsky
2020-12-09 12:29 ` Peter Zijlstra
2020-12-09 8:07 ` Peter Zijlstra
2020-12-01 20:53 ` [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog_lock John Ogness
2020-12-04 6:41 ` Sergey Senozhatsky
2020-12-06 20:44 ` John Ogness
2020-12-04 15:52 ` devkmsg: was " Petr Mladek
2020-12-06 20:51 ` John Ogness
2020-12-07 9:56 ` Petr Mladek
2020-12-04 15:57 ` syslog: was: " Petr Mladek
2020-12-06 21:06 ` John Ogness
2020-12-07 10:01 ` Petr Mladek
2020-12-04 16:10 ` recursion handling: " Petr Mladek
2020-12-05 4:25 ` Sergey Senozhatsky
2020-12-06 22:08 ` John Ogness
2020-12-05 9:41 ` Sergey Senozhatsky
2020-12-06 22:17 ` John Ogness
2020-12-06 21:44 ` John Ogness
2020-12-07 11:17 ` Petr Mladek
2020-12-04 16:15 ` vprintk_store: was: " Petr Mladek
2020-12-06 22:30 ` John Ogness
2020-12-07 12:46 ` Petr Mladek
2020-12-04 16:19 ` consoles: " Petr Mladek
2020-12-05 4:39 ` Sergey Senozhatsky
2020-12-07 9:50 ` Petr Mladek [this message]
2020-12-08 20:51 ` Sergey Senozhatsky
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