From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: John Ogness <john.ogness@linutronix.de>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH next v2 2/3] printk: change @clear_seq to atomic64_t
Date: Wed, 9 Dec 2020 05:34:19 +0900 [thread overview]
Message-ID: <X8/jS9k/eMIL+Acw@jagdpanzerIV.localdomain> (raw)
In-Reply-To: <X8n9a2DWUFE/giyB@alley>
On (20/12/04 10:12), Petr Mladek wrote:
> On Tue 2020-12-01 21:59:40, John Ogness wrote:
> > Currently @clear_seq access is protected by @logbuf_lock. Once
> > @logbuf_lock is removed some other form of synchronization will be
> > required. Change the type of @clear_seq to atomic64_t to provide the
> > synchronization.
> >
> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index fc5e3a7d6d89..e9018c4e1b66 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -3412,7 +3418,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
> > */
> > void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
> > {
> > - dumper->cur_seq = clear_seq;
> > + dumper->cur_seq = atomic64_read(&clear_seq);
>
> Sigh, atomic64_read() uses a spin lock in the generic implementation
> that is used on some architectures.
Oh... So on those archs prb is not lockless in fact, it actually
takes the spin_lock each time we read the descriptor state?
desc_read()
atomic_long_read(state_var)
atomic64_read()
raw_spin_lock_irqsave(lock, flags)
<< NMI panic >>
Am I missing something?
-ss
next prev parent reply other threads:[~2020-12-08 20:35 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 [this message]
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
2020-12-08 20:51 ` Sergey Senozhatsky
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