From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andrea Parri <andrea.parri@amarulasolutions.com>,
Thomas Gleixner <tglx@linutronix.de>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer implementation
Date: Tue, 25 Jun 2019 17:55:48 +0900 [thread overview]
Message-ID: <20190625085548.GA532@jagdpanzerIV> (raw)
In-Reply-To: <20190607162349.18199-2-john.ogness@linutronix.de>
On (06/07/19 18:29), John Ogness wrote:
[..]
> +static void add_descr_list(struct prb_reserved_entry *e)
> +{
> + struct printk_ringbuffer *rb = e->rb;
> + struct prb_list *l = &rb->descr_list;
> + struct prb_descr *d = e->descr;
> + struct prb_descr *newest_d;
> + unsigned long newest_id;
> +
> + /* set as newest */
> + do {
> + /* MB5: synchronize add descr */
> + newest_id = smp_load_acquire(&l->newest);
> + newest_d = TO_DESCR(rb, newest_id);
> +
> + if (newest_id == EOL)
> + WRITE_ONCE(d->seq, 1);
> + else
> + WRITE_ONCE(d->seq, READ_ONCE(newest_d->seq) + 1);
> + /*
> + * MB5: synchronize add descr
> + *
> + * In particular: next written before cmpxchg
> + */
> + } while (cmpxchg_release(&l->newest, newest_id, e->id) != newest_id);
> +
> + if (unlikely(newest_id == EOL)) {
> + /* no previous newest means we *are* the list, set oldest */
> +
> + /*
> + * MB UNPAIRED
> + *
> + * In particular: Force cmpxchg _after_ cmpxchg on newest.
> + */
> + WARN_ON_ONCE(cmpxchg_release(&l->oldest, EOL, e->id) != EOL);
> + } else {
> + /* link to previous chain */
> +
> + /*
> + * MB6: synchronize link descr
> + *
> + * In particular: Force cmpxchg _after_ cmpxchg on newest.
> + */
> + WARN_ON_ONCE(cmpxchg_release(&newest_d->next,
> + EOL, e->id) != EOL);
> + }
> +}
[..]
> +char *prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
> + unsigned int size)
> +{
> + struct prb_datablock *b;
> + struct prb_descr *d;
> + char *buf;
> +
> + if (size == 0)
> + return NULL;
> +
> + size += sizeof(struct prb_datablock);
> + size = DATA_ALIGN_SIZE(size);
> + if (size > DATAARRAY_SIZE(rb))
> + return NULL;
> +
> + e->rb = rb;
> +
> + local_irq_save(e->irqflags);
> +
> + if (!assign_descr(e))
> + goto err_out;
> +
> + d = e->descr;
> + WRITE_ONCE(d->id, e->id);
> +
> + if (!data_reserve(e, size)) {
> + /* put invalid descriptor on list, can still be traversed */
> + WRITE_ONCE(d->next, EOL);
> + add_descr_list(e);
> + goto err_out;
> + }
I'm wondering if prb can always report about its problems. Including the
cases when things "go rather bad".
Suppose we have
printk()
prb_reserve()
!data_reserve()
add_descr_list()
WARN_ON_ONCE()
printk()
prb_reserve()
!assign_descr(e) << lost WARN_ON's "printk" or "printks"?
In general, assuming that there might be more error printk-s either
called directly directly from prb->printk on indirectly, from
prb->ABC->printk.
Also note,
Lost printk-s are not going to be accounted as 'lost' automatically.
It seems that for printk() there is no way to find out that it has
recursed from printk->prb_commit but hasn't succeeded in storing
recursive messages. I'd say that prb_reserve() err_out should probably
&rb->lost++.
-ss
next prev parent reply other threads:[~2019-06-25 8:55 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-07 16:23 [RFC PATCH v2 0/2] printk: new ringbuffer implementation John Ogness
2019-06-07 16:23 ` [RFC PATCH v2 1/2] printk-rb: add a new printk " John Ogness
2019-06-18 4:51 ` Sergey Senozhatsky
2019-06-18 22:12 ` John Ogness
2019-06-25 6:45 ` Sergey Senozhatsky
2019-06-25 7:15 ` Sergey Senozhatsky
2019-06-25 8:44 ` John Ogness
2019-06-25 9:06 ` Petr Mladek
2019-06-25 10:03 ` Sergey Senozhatsky
2019-06-25 12:03 ` John Ogness
2019-06-26 2:08 ` Sergey Senozhatsky
2019-06-26 7:16 ` John Ogness
2019-06-26 7:45 ` Sergey Senozhatsky
2019-06-26 7:47 ` Petr Mladek
2019-06-26 7:59 ` Sergey Senozhatsky
2019-06-25 9:09 ` Sergey Senozhatsky
2019-06-18 11:12 ` Peter Zijlstra
2019-06-18 22:18 ` John Ogness
2019-06-18 11:22 ` Peter Zijlstra
2019-06-18 22:30 ` John Ogness
2019-06-19 10:46 ` Andrea Parri
2019-06-20 22:50 ` John Ogness
2019-06-21 12:16 ` Andrea Parri
2019-06-19 11:08 ` Peter Zijlstra
2019-06-18 11:47 ` Peter Zijlstra
2019-06-20 22:23 ` John Ogness
2019-06-26 22:40 ` Peter Zijlstra
2019-06-26 22:53 ` Peter Zijlstra
2019-06-28 9:50 ` John Ogness
2019-06-28 15:44 ` Peter Zijlstra
2019-06-28 16:07 ` Peter Zijlstra
2019-07-01 10:39 ` John Ogness
2019-07-01 14:10 ` Peter Zijlstra
2019-07-01 14:11 ` Peter Zijlstra
2019-06-29 21:05 ` Andrea Parri
2019-06-30 2:03 ` John Ogness
2019-06-30 14:08 ` Andrea Parri
2019-07-02 14:13 ` John Ogness
2019-06-26 22:47 ` Peter Zijlstra
2019-06-21 14:05 ` Petr Mladek
2019-06-24 8:33 ` John Ogness
2019-06-24 14:09 ` Petr Mladek
2019-06-25 13:29 ` John Ogness
2019-06-26 8:29 ` Petr Mladek
2019-06-26 9:09 ` John Ogness
2019-06-26 21:16 ` Peter Zijlstra
2019-06-26 21:43 ` John Ogness
2019-06-27 8:28 ` Petr Mladek
2019-07-04 10:33 ` [PATCH POC] printk_ringbuffer: Alternative implementation of lockless printk ringbuffer Petr Mladek
2019-07-04 14:59 ` John Ogness
2019-07-08 15:23 ` Petr Mladek
2019-07-09 1:34 ` John Ogness
2019-07-09 9:06 ` Petr Mladek
2019-07-09 10:21 ` John Ogness
2019-07-09 11:58 ` Petr Mladek
2019-08-14 3:46 ` John Ogness
2019-06-24 13:55 ` [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer implementation John Ogness
2019-06-25 8:55 ` Sergey Senozhatsky [this message]
2019-06-25 9:19 ` John Ogness
2019-06-07 16:23 ` [RFC PATCH v2 2/2] printk-rb: add test module John Ogness
2019-06-17 21:09 ` [RFC PATCH v2 0/2] printk: new ringbuffer implementation Thomas Gleixner
2019-06-18 7:15 ` Petr Mladek
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