From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Petr Mladek <pmladek@suse.com>,
Peter Zijlstra <peterz@infradead.org>,
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: [PATCH 2/2] printk: use the lockless ringbuffer
Date: Thu, 13 Feb 2020 20:59:57 +0900 [thread overview]
Message-ID: <20200213115957.GC36551@google.com> (raw)
In-Reply-To: <87v9oarfg4.fsf@linutronix.de>
On (20/02/13 10:42), John Ogness wrote:
> On 2020-02-13, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote:
> >> - while (user->seq == log_next_seq) {
> >> + if (!prb_read_valid(prb, user->seq, r)) {
> >> if (file->f_flags & O_NONBLOCK) {
> >> ret = -EAGAIN;
> >> logbuf_unlock_irq();
> >> @@ -890,30 +758,26 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
> >>
> >> logbuf_unlock_irq();
> >> ret = wait_event_interruptible(log_wait,
> >> - user->seq != log_next_seq);
> >> + prb_read_valid(prb, user->seq, r));
> >> if (ret)
> >> goto out;
> >> logbuf_lock_irq();
> >> }
> >>
> >> - if (user->seq < log_first_seq) {
> >> - /* our last seen message is gone, return error and reset */
> >> - user->idx = log_first_idx;
> >> - user->seq = log_first_seq;
> >> + if (user->seq < r->info->seq) {
> >> + /* the expected message is gone, return error and reset */
> >> + user->seq = r->info->seq;
> >> ret = -EPIPE;
> >> logbuf_unlock_irq();
> >> goto out;
> >> }
> >
> > Sorry, why doesn't this do something like
> >
> > if (user->seq < prb_first_seq(prb)) {
> > /* the expected message is gone, return error and reset */
> > user->seq = prb_first_seq(prb);
> > ret = -EPIPE;
> > ...
> > }
>
> Here prb_read_valid() was successful, so a record _was_ read. The
> kerneldoc for the prb_read_valid() says:
Hmm, yeah. That's true.
OK, something weird...
I ran some random printk-pressure test (mostly printks from IRQs;
+ some NMI printk-s, but they are routed through nmi printk-safe
buffers; + some limited number of printk-safe printk-s, routed
via printk-safe buffer (so, once again, IRQ); + user-space
journalctl -f syslog reader), and after the test 'cat /dev/kmsg'
is terminally broken
[..]
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
cat /dev/kmsg
cat: /dev/kmsg: Broken pipe
[..]
dmesg works. Reading from /dev/kmsg - doesn't; it did work, however,
before the test.
So I printed seq numbers from devksmg read to a seq buffer and dumped
it via procfs, just seq numbers before we adjust user->seq (set to
r->seq) and after
+ offt += snprintf(BUF + offt,
+ sizeof(BUF) - offt,
+ "%s: devkmsg_read() error %llu %llu %llu\n",
+ current->comm,
+ user->seq,
+ r->info->seq,
+ prb_first_seq(prb));
...
systemd-journal: devkmsg_read() error 1979235 1979236 1979236
systemd-journal: corrected seq 1979236 1979236
systemd-journal: devkmsg_read() error 1979237 1979243 1979243
systemd-journal: corrected seq 1979243 1979243
systemd-journal: devkmsg_read() error 1979244 1979250 1979250
systemd-journal: corrected seq 1979250 1979250
systemd-journal: devkmsg_read() error 1979251 1979257 1979257
systemd-journal: corrected seq 1979257 1979257
systemd-journal: devkmsg_read() error 1979258 1979265 1979265
systemd-journal: corrected seq 1979265 1979265
systemd-journal: devkmsg_read() error 1979266 1979272 1979272
systemd-journal: corrected seq 1979272 1979272
systemd-journal: devkmsg_read() error 1979272 1979273 1979273
systemd-journal: corrected seq 1979273 1979273
systemd-journal: devkmsg_read() error 1979274 1979280 1979280
systemd-journal: corrected seq 1979280 1979280
systemd-journal: devkmsg_read() error 1979281 1982465 1980933
systemd-journal: corrected seq 1982465 1982465
cat: devkmsg_read() error 1980987 1982531 1980987
cat: corrected seq 1982531 1982531
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981015 1982563 1981015
cat: corrected seq 1982563 1982563
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981080 1982633 1981080
cat: corrected seq 1982633 1982633
cat: devkmsg_read() error 1981095 1982652 1981095
cat: corrected seq 1982652 1982652
cat: devkmsg_read() error 1981095 1982652 1981095
cat: corrected seq 1982652 1982652
cat: devkmsg_read() error 1981095 1982652 1981095
cat: corrected seq 1982652 1982652
cat: devkmsg_read() error 1981095 1982652 1981095
cat: corrected seq 1982652 1982652
cat: devkmsg_read() error 1981095 1982652 1981095
cat: corrected seq 1982652 1982652
cat: devkmsg_read() error 1981095 1982652 1981095
cat: corrected seq 1982652 1982652
cat: devkmsg_read() error 1981095 1982652 1981095
cat: corrected seq 1982652 1982652
...
What's up with that user->seq counter?
-ss
next prev parent reply other threads:[~2020-02-13 12:00 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
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 [this message]
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
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