From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
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>,
Andrea Parri <parri.andrea@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
kexec@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: misc nits Re: [PATCH 1/2] printk: add lockless buffer
Date: Mon, 2 Mar 2020 13:32:49 +0100 [thread overview]
Message-ID: <20200302123249.6khdqpneu7t6l35s@pathway.suse.cz> (raw)
In-Reply-To: <87r1ybujm5.fsf@linutronix.de>
On Mon 2020-03-02 11:38:42, John Ogness wrote:
> On 2020-02-21, Petr Mladek <pmladek@suse.com> wrote:
> >> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
> >> new file mode 100644
> >> index 000000000000..796257f226ee
> >> --- /dev/null
> >> +++ b/kernel/printk/printk_ringbuffer.c
> >> +/*
> >> + * Read the record @id and verify that it is committed and has the sequence
> >> + * number @seq. On success, 0 is returned.
> >> + *
> >> + * Error return values:
> >> + * -EINVAL: A committed record @seq does not exist.
> >> + * -ENOENT: The record @seq exists, but its data is not available. This is a
> >> + * valid record, so readers should continue with the next seq.
> >> + */
> >> +static int desc_read_committed(struct prb_desc_ring *desc_ring,
> >> + unsigned long id, u64 seq,
> >> + struct prb_desc *desc)
> >> +{
> >
> > I was few times confused whether this function reads the descriptor
> > a safe way or not.
> >
> > Please, rename it to make it clear that does only a check.
> > For example, check_state_commited().
>
> This function _does_ read. It is a helper function of prb_read() to
> _read_ the descriptor. It is an extended version of desc_read() that
> also performs various checks that the descriptor is committed.
I see.
> I will update the function description to be more similar to desc_read()
> so that it is obvious that it is "getting a copy of a specified
> descriptor".
OK, what about having desc_read_by_seq() instead?
Also there is a bug in current desc_read_commited().
desc->info.seq might contain a garbage when d_state is desc_miss
or desc_reserved.
I would change it to:
static enum desc_state
desc_read_by_seq(struct prb_desc_ring *desc_ring,
u64 seq, struct prb_desc *desc)
{
struct prb_desc *rdesc = to_desc(desc_ring, seq);
atomic_long_t *state_var = &rdesc->state_var;
id = DESC_ID(atomic_long_read(state_var));
enum desc_state d_state;
d_state = desc_read(desc_ring, id, desc);
if (d_state == desc_miss ||
d_state == desc_reserved ||
desc->info.seq != seq)
return -EINVAL;
if (d_state == desc_reusable)
return -ENOENT;
if (d_state != desc_committed)
return -EINVAL;
return 0;
}
Best Regards,
Petr
PS: I am going to dive into the barriers again to answer the last
letter about them.
next prev parent reply other threads:[~2020-03-02 12:32 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-28 16:19 [PATCH 0/2] printk: replace ringbuffer John Ogness
2020-01-28 16:19 ` [PATCH 1/2] printk: add lockless buffer John Ogness
2020-01-29 3:53 ` Steven Rostedt
2020-02-21 11:54 ` more barriers: " Petr Mladek
2020-02-27 12:04 ` John Ogness
2020-03-04 15:08 ` Petr Mladek
2020-03-13 10:13 ` John Ogness
2020-02-21 12:05 ` misc nits " Petr Mladek
2020-03-02 10:38 ` John Ogness
2020-03-02 12:17 ` Joe Perches
2020-03-02 12:32 ` Petr Mladek [this message]
2020-03-02 13:43 ` John Ogness
2020-03-03 9:47 ` Petr Mladek
2020-03-03 15:42 ` John Ogness
2020-03-04 10:09 ` Petr Mladek
2020-03-04 9:40 ` Petr Mladek
2020-01-28 16:19 ` [PATCH 2/2] printk: use the lockless ringbuffer John Ogness
2020-02-13 9:07 ` Sergey Senozhatsky
2020-02-13 9:42 ` John Ogness
2020-02-13 11:59 ` Sergey Senozhatsky
2020-02-13 22:36 ` John Ogness
2020-02-14 1:41 ` Sergey Senozhatsky
2020-02-14 2:09 ` Sergey Senozhatsky
2020-02-14 9:48 ` John Ogness
2020-02-14 13:29 ` lijiang
2020-02-14 13:50 ` John Ogness
2020-02-15 4:15 ` lijiang
2020-02-17 15:40 ` crashdump: " Petr Mladek
2020-02-17 16:14 ` John Ogness
2020-02-17 14:41 ` misc details: " Petr Mladek
2020-02-25 20:11 ` John Ogness
2020-02-26 9:54 ` Petr Mladek
2020-02-05 4:25 ` [PATCH 0/2] printk: replace ringbuffer lijiang
2020-02-05 4:42 ` Sergey Senozhatsky
2020-02-05 4:48 ` Sergey Senozhatsky
2020-02-05 5:02 ` Sergey Senozhatsky
2020-02-05 5:38 ` lijiang
2020-02-05 6:36 ` Sergey Senozhatsky
2020-02-05 9:00 ` John Ogness
2020-02-05 9:28 ` Sergey Senozhatsky
2020-02-05 10:19 ` lijiang
2020-02-05 16:12 ` John Ogness
2020-02-06 9:12 ` lijiang
2020-02-13 13:07 ` Petr Mladek
2020-02-14 1:07 ` Sergey Senozhatsky
2020-02-05 11:07 ` Sergey Senozhatsky
2020-02-05 15:48 ` John Ogness
2020-02-05 19:29 ` Joe Perches
2020-02-06 6:31 ` Sergey Senozhatsky
2020-02-06 7:30 ` lijiang
2020-02-07 1:40 ` Steven Rostedt
2020-02-07 7:43 ` John Ogness
2020-02-14 15:56 ` Petr Mladek
2020-02-17 11:13 ` John Ogness
2020-02-17 14:50 ` Petr Mladek
2020-02-25 19:27 ` John Ogness
2020-02-05 9:36 ` lijiang
2020-02-06 9:21 ` lijiang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200302123249.6khdqpneu7t6l35s@pathway.suse.cz \
--to=pmladek@suse.com \
--cc=gregkh@linuxfoundation.org \
--cc=john.ogness@linutronix.de \
--cc=kexec@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=parri.andrea@gmail.com \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=sergey.senozhatsky.work@gmail.com \
--cc=sergey.senozhatsky@gmail.com \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).