From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Daniel Wang <wonderfly@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
Jiri Slaby <jslaby@suse.com>, Peter Feiner <pfeiner@google.com>,
linux-serial@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [RFC PATCH v1 06/25] printk-rb: add blocking reader support
Date: Mon, 18 Feb 2019 15:05:38 +0100 [thread overview]
Message-ID: <20190218140538.5sug36qiji2rurxx@pathway.suse.cz> (raw)
In-Reply-To: <20190212143003.48446-7-john.ogness@linutronix.de>
On Tue 2019-02-12 15:29:44, John Ogness wrote:
> Add a blocking read function for readers. An irq_work function is
> used to signal the wait queue so that write notification can
> be triggered from any context.
I would be more precise what exacly is problematic in which context.
Something like:
An irq_work function is used because wake_up() cannot be called safely
from NMI and scheduler context.
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
> include/linux/printk_ringbuffer.h | 20 ++++++++++++++++
> lib/printk_ringbuffer.c | 49 +++++++++++++++++++++++++++++++++++++++
> 2 files changed, 69 insertions(+)
>
> diff --git a/include/linux/printk_ringbuffer.h b/include/linux/printk_ringbuffer.h
> index 5fdaf632c111..106f20ef8b4d 100644
> --- a/include/linux/printk_ringbuffer.h
> +++ b/include/linux/printk_ringbuffer.h
> @@ -2,8 +2,10 @@
> #ifndef _LINUX_PRINTK_RINGBUFFER_H
> #define _LINUX_PRINTK_RINGBUFFER_H
>
> +#include <linux/irq_work.h>
> #include <linux/atomic.h>
> #include <linux/percpu.h>
> +#include <linux/wait.h>
>
> struct prb_cpulock {
> atomic_t owner;
> @@ -22,6 +24,10 @@ struct printk_ringbuffer {
>
> struct prb_cpulock *cpulock;
> atomic_t ctx;
> +
> + struct wait_queue_head *wq;
> + atomic_long_t wq_counter;
> + struct irq_work *wq_work;
> };
>
> struct prb_entry {
> @@ -59,6 +65,15 @@ struct prb_iterator {
> #define DECLARE_STATIC_PRINTKRB(name, szbits, cpulockptr) \
> static char _##name##_buffer[1 << (szbits)] \
> __aligned(__alignof__(long)); \
> +static DECLARE_WAIT_QUEUE_HEAD(_##name##_wait); \
> +static void _##name##_wake_work_func(struct irq_work *irq_work) \
> +{ \
> + wake_up_interruptible_all(&_##name##_wait); \
> +} \
All ring buffers might share the same generic function, something like:
void prb_wake_readers_work_func(struct irq_work *irq_work)
{
struct printk_ringbuffer *rb;
rb = container_of(irq_work, struct printk_ring_buffer, wq_work);
wake_up_interruptible_all(rb->wq); \
}
> +static struct irq_work _##name##_wake_work = { \
> + .func = _##name##_wake_work_func, \
> + .flags = IRQ_WORK_LAZY, \
> +}; \
> static struct printk_ringbuffer name = { \
> .buffer = &_##name##_buffer[0], \
> .size_bits = szbits, \
> diff --git a/lib/printk_ringbuffer.c b/lib/printk_ringbuffer.c
> index 1d1e886a0966..c2ddf4cb9f92 100644
> --- a/lib/printk_ringbuffer.c
> +++ b/lib/printk_ringbuffer.c
> @@ -185,6 +188,12 @@ void prb_commit(struct prb_handle *h)
> }
>
> prb_unlock(rb->cpulock, h->cpu);
> +
> + if (changed) {
> + atomic_long_inc(&rb->wq_counter);
> + if (wq_has_sleeper(rb->wq))
> + irq_work_queue(rb->wq_work);
> + }
> }
>
> /*
> @@ -437,3 +446,43 @@ int prb_iter_next(struct prb_iterator *iter, char *buf, int size, u64 *seq)
>
> return 1;
> }
> +
> +/*
> + * prb_iter_wait_next: Advance to the next record, blocking if none available.
> + * @iter: Iterator tracking the current position.
> + * @buf: A buffer to store the data of the next record. May be NULL.
> + * @size: The size of @buf. (Ignored if @buf is NULL.)
> + * @seq: The sequence number of the next record. May be NULL.
> + *
> + * If a next record is already available, this function works like
> + * prb_iter_next(). Otherwise block interruptible until a next record is
> + * available.
> + *
> + * When a next record is available, @iter is advanced and (if specified)
> + * the data and/or sequence number of that record are provided.
> + *
> + * This function might sleep.
> + *
> + * Returns 1 if @iter was advanced, -EINVAL if @iter is now invalid, or
> + * -ERESTARTSYS if interrupted by a signal.
> + */
> +int prb_iter_wait_next(struct prb_iterator *iter, char *buf, int size, u64 *seq)
> +{
> + unsigned long last_seen;
> + int ret;
> +
> + for (;;) {
> + last_seen = atomic_long_read(&iter->rb->wq_counter);
> +
> + ret = prb_iter_next(iter, buf, size, seq);
> + if (ret != 0)
> + break;
> +
> + ret = wait_event_interruptible(*iter->rb->wq,
> + last_seen != atomic_long_read(&iter->rb->wq_counter));
Do we really need yet another counter here?
I think that rb->seq might do the same job. Or if there is problem
with atomicity then rb->head might work as well. Or do I miss
anything?
Best Regards,
Petr
> + if (ret < 0)
> + break;
> + }
> +
> + return ret;
> +}
> --
> 2.11.0
>
next prev parent reply other threads:[~2019-02-18 14:05 UTC|newest]
Thread overview: 147+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-12 14:29 [RFC PATCH v1 00/25] printk: new implementation John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 01/25] printk-rb: add printk ring buffer documentation John Ogness
2019-02-12 14:45 ` Greg Kroah-Hartman
2019-02-12 14:29 ` [RFC PATCH v1 02/25] printk-rb: add prb locking functions John Ogness
2019-02-13 15:45 ` Petr Mladek
2019-02-13 21:39 ` John Ogness
2019-02-14 10:33 ` Petr Mladek
2019-02-14 12:10 ` John Ogness
2019-02-15 10:26 ` Petr Mladek
2019-02-15 10:56 ` John Ogness
2019-03-07 2:12 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 03/25] printk-rb: define ring buffer struct and initializer John Ogness
2019-02-12 14:46 ` Greg Kroah-Hartman
2019-02-14 12:46 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 04/25] printk-rb: add writer interface John Ogness
2019-02-14 15:16 ` Petr Mladek
2019-02-14 23:36 ` John Ogness
2019-02-15 1:19 ` John Ogness
2019-02-15 13:47 ` Petr Mladek
2019-02-17 1:32 ` John Ogness
2019-02-21 13:51 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 05/25] printk-rb: add basic non-blocking reading interface John Ogness
2019-02-18 12:54 ` Petr Mladek
2019-02-19 21:44 ` John Ogness
2019-02-21 16:22 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 06/25] printk-rb: add blocking reader support John Ogness
2019-02-18 14:05 ` Petr Mladek [this message]
2019-02-19 21:47 ` John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 07/25] printk-rb: add functionality required by printk John Ogness
2019-02-12 17:15 ` Linus Torvalds
2019-02-13 9:20 ` John Ogness
2019-02-18 15:59 ` Petr Mladek
2019-02-19 22:08 ` John Ogness
2019-02-22 9:58 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 08/25] printk: add ring buffer and kthread John Ogness
2019-02-12 15:47 ` Sergey Senozhatsky
2019-02-19 13:54 ` Petr Mladek
2019-03-04 7:38 ` Sergey Senozhatsky
2019-03-04 10:00 ` Sergey Senozhatsky
2019-03-04 11:07 ` Sergey Senozhatsky
2019-03-05 21:00 ` John Ogness
2019-03-06 15:57 ` Petr Mladek
2019-03-06 21:17 ` John Ogness
2019-03-06 22:22 ` John Ogness
2019-03-07 6:41 ` Sergey Senozhatsky
2019-03-07 6:51 ` Sergey Senozhatsky
2019-03-07 12:50 ` Petr Mladek
2019-03-07 5:15 ` Sergey Senozhatsky
2019-03-11 10:51 ` John Ogness
2019-03-12 9:58 ` Sergey Senozhatsky
2019-03-12 10:30 ` Petr Mladek
2019-03-07 12:06 ` John Ogness
2019-03-08 1:31 ` Sergey Senozhatsky
2019-03-08 10:04 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 09/25] printk: remove exclusive console hack John Ogness
2019-02-19 14:03 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 10/25] printk: redirect emit/store to new ringbuffer John Ogness
2019-02-20 9:01 ` Petr Mladek
2019-02-20 21:25 ` John Ogness
2019-02-22 14:43 ` Petr Mladek
2019-02-22 15:06 ` John Ogness
2019-02-22 15:25 ` Petr Mladek
2019-02-25 12:11 ` Petr Mladek
2019-02-25 16:41 ` John Ogness
2019-02-26 9:45 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 11/25] printk_safe: remove printk safe code John Ogness
2019-02-22 10:37 ` Petr Mladek
2019-02-22 13:38 ` John Ogness
2019-02-22 15:15 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 12/25] printk: minimize console locking implementation John Ogness
2019-02-25 13:44 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 13/25] printk: track seq per console John Ogness
2019-02-25 14:59 ` Petr Mladek
2019-02-26 8:45 ` John Ogness
2019-02-26 13:11 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 14/25] printk: do boot_delay_msec inside printk_delay John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 15/25] printk: print history for new consoles John Ogness
2019-02-26 14:58 ` Petr Mladek
2019-02-26 15:22 ` John Ogness
2019-02-27 9:02 ` Petr Mladek
2019-02-27 10:02 ` John Ogness
2019-02-27 13:12 ` Petr Mladek
2019-03-04 9:24 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 16/25] printk: implement CON_PRINTBUFFER John Ogness
2019-02-26 15:38 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 17/25] printk: add processor number to output John Ogness
2019-02-13 22:29 ` John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 18/25] console: add write_atomic interface John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 19/25] printk: introduce emergency messages John Ogness
2019-03-07 7:30 ` Sergey Senozhatsky
2019-03-08 10:31 ` Petr Mladek
2019-03-11 12:04 ` John Ogness
2019-03-12 2:51 ` Sergey Senozhatsky
2019-03-12 2:58 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 20/25] serial: 8250: implement write_atomic John Ogness
2019-02-27 9:46 ` Petr Mladek
2019-02-27 10:32 ` John Ogness
2019-02-27 13:55 ` Petr Mladek
2019-03-08 4:05 ` John Ogness
2019-03-08 4:17 ` John Ogness
2019-03-08 10:28 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 21/25] printk: implement KERN_CONT John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 22/25] printk: implement /dev/kmsg John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 23/25] printk: implement syslog John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 24/25] printk: implement kmsg_dump John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 25/25] printk: remove unused code John Ogness
2019-03-08 14:02 ` Sebastian Andrzej Siewior
2019-03-11 2:46 ` Sergey Senozhatsky
2019-03-11 8:18 ` Sebastian Andrzej Siewior
2019-03-12 9:38 ` Petr Mladek
2019-02-13 1:31 ` [RFC PATCH v1 00/25] printk: new implementation Sergey Senozhatsky
2019-02-13 13:43 ` John Ogness
2019-03-04 6:39 ` Sergey Senozhatsky
2019-02-13 1:41 ` Sergey Senozhatsky
2019-02-13 14:15 ` John Ogness
2019-03-04 5:31 ` Sergey Senozhatsky
2019-02-13 2:55 ` Sergey Senozhatsky
2019-02-13 14:43 ` John Ogness
2019-03-04 5:23 ` Sergey Senozhatsky
2019-03-07 9:53 ` John Ogness
2019-03-08 10:00 ` Petr Mladek
2019-03-11 10:54 ` Sergey Senozhatsky
2019-03-12 12:38 ` Petr Mladek
2019-03-12 15:15 ` John Ogness
2019-03-13 2:15 ` Sergey Senozhatsky
2019-03-13 8:19 ` John Ogness
2019-03-13 8:40 ` Sebastian Siewior
2019-03-13 9:27 ` Sergey Senozhatsky
2019-03-13 10:06 ` Sergey Senozhatsky
2019-03-14 9:27 ` Petr Mladek
2019-03-13 8:46 ` Sergey Senozhatsky
2019-03-14 9:14 ` Petr Mladek
2019-03-14 9:35 ` John Ogness
2019-03-13 2:00 ` Sergey Senozhatsky
2019-02-13 16:54 ` David Laight
2019-02-13 22:20 ` John Ogness
2020-01-20 23:05 ` Eugeniu Rosca
2020-01-21 23:56 ` John Ogness
2020-01-22 2:34 ` Eugeniu Rosca
2020-01-22 7:31 ` Geert Uytterhoeven
2020-01-22 16:58 ` Eugeniu Rosca
2020-01-22 19:48 ` Geert Uytterhoeven
2020-01-24 16:09 ` Eugeniu Rosca
2020-01-27 12:32 ` Petr Mladek
2020-01-27 13:45 ` Eugeniu Rosca
2020-01-22 10:33 ` John Ogness
2020-01-24 12:13 ` Eugeniu Rosca
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