From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH printk v2 3/4] printk: Skip unfinalized records in panic
Date: Wed, 18 Oct 2023 17:56:52 +0206 [thread overview]
Message-ID: <87zg0g53qb.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <ZS_5Xd7zPWvSHuqq@alley>
On 2023-10-18, Petr Mladek <pmladek@suse.com> wrote:
> So it is the _last_ finalized id from the timing POV. If there are
> more CPUs storing and finalizing the messages in parallel then
> it might change forth and back. There might be earlier non-finalized
> records and newer finalized ones.
>
> It means that prb_next_seq() really is the best effort and
> the description is not valid:
Well, the description was valid until prb_next_seq() was optimized and
converted to best-effort with:
commit f244b4dc53e5 ("printk: ringbuffer: Improve prb_next_seq() performance")
> It would be great to document these subtle details especially when
> we are going to depend on them.
Going through the various call sites of prb_next_seq(), I would argue
that the above optimization introduced some bugs. I will investigate if
prb_next_seq() can be fixed to match its description because the current
users already depend on that.
WRT to this series, I have put together an alternative implementation
that does not use prb_next_seq().
John
next prev parent reply other threads:[~2023-10-18 15:51 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-13 20:43 [PATCH printk v2 0/4] fix console flushing on panic John Ogness
2023-10-13 20:43 ` [PATCH printk v2 1/4] printk: For @suppress_panic_printk check other panic John Ogness
2023-10-16 13:05 ` Petr Mladek
2023-10-13 20:43 ` [PATCH printk v2 2/4] printk: Add this_cpu_in_panic() John Ogness
2023-10-16 13:14 ` Petr Mladek
2023-10-13 20:43 ` [PATCH printk v2 3/4] printk: Skip unfinalized records in panic John Ogness
2023-10-17 11:27 ` Petr Mladek
2023-10-17 21:25 ` John Ogness
2023-10-18 8:24 ` John Ogness
2023-10-18 13:15 ` Petr Mladek
2023-10-18 12:54 ` Petr Mladek
2023-10-18 13:45 ` John Ogness
2023-10-18 15:27 ` Petr Mladek
2023-10-18 15:50 ` John Ogness [this message]
2023-10-19 10:29 ` Petr Mladek
2023-10-18 14:20 ` Petr Mladek
2023-10-23 9:53 ` John Ogness
2023-10-13 20:43 ` [PATCH printk v2 4/4] printk: Ignore waiter on panic John Ogness
2023-10-18 9:56 ` Petr Mladek
2023-10-23 9:15 ` John Ogness
2023-10-13 20:46 ` [PATCH printk v2 0/4] fix console flushing " John Ogness
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