From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH v2] printk: Relocate wake_klogd check close to the end of console_unlock()
Date: Thu, 8 Feb 2018 23:53:07 +0900 [thread overview]
Message-ID: <20180208145307.GA485@tigerII.localdomain> (raw)
In-Reply-To: <20180208130402.15157-1-pmladek@suse.com>
On (02/08/18 14:04), Petr Mladek wrote:
> We mark for waking up klogd whenever we see a new message sequence in
> the main loop. However, the actual wakeup is always at the end of the
> function and we can easily test for the wakeup condition when we do
> the final should-we-repeat check.
>
> Move the wake_klogd condition check out of the main loop. This avoids
> doing the same thing repeatedly and groups similar checks into a
> common place.
>
> This fixes a race introduced by the commit dbdda842fe96f8932 ("printk: Add
> console owner and waiter logic to load balance console writes").
> The current console owner might process the newly added message before
> the related printk() start waiting for the console lock. Then the lock
> is passed without waking klogd. The new owner sees the already updated
> seen_seq and does not know that the wakeup is needed.
I need to do more "research" on this. I though about it some time ago,
and I think that waking up klogd _only_ when we don't have any pending
logbuf messages still can be pretty late. Can't it? We can spin in
console_unlock() printing loop for a long time, probably passing
console_sem ownership between CPUs, without waking up the log_wait waiter.
May be we can wake it up from the printing loop, outside of logbuf_lock,
and let klogd to compete for logbuf_lock with the printing CPU. Why do
we wake it up only when we are done pushing messages to a potentially
slow serial console?
-ss
next prev parent reply other threads:[~2018-02-08 14:53 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-08 13:04 [PATCH v2] printk: Relocate wake_klogd check close to the end of console_unlock() Petr Mladek
2018-02-08 14:53 ` Sergey Senozhatsky [this message]
2018-02-08 16:48 ` Petr Mladek
2018-02-09 3:28 ` Sergey Senozhatsky
2018-02-09 10:39 ` Petr Mladek
2018-02-10 7:33 ` Sergey Senozhatsky
2018-02-09 10:47 ` Petr Mladek
2018-02-19 15:58 ` Petr Mladek
2018-02-19 16:01 ` [PATCH v3] " Petr Mladek
2018-02-26 6:37 ` Sergey Senozhatsky
2018-02-26 15:57 ` Petr Mladek
2018-02-26 16:01 ` Sergey Senozhatsky
2018-02-26 6:27 ` [PATCH v2] " Sergey Senozhatsky
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