From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: 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>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: devkmsg: was [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog_lock
Date: Sun, 06 Dec 2020 21:57:46 +0106 [thread overview]
Message-ID: <87y2iamzdp.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <X8pbQ94Buqxhlqsk@alley>
On 2020-12-04, Petr Mladek <pmladek@suse.com> wrote:
>> Since the ringbuffer is lockless, there is no need for it to be
>> protected by @logbuf_lock. Remove @logbuf_lock.
>
> It might make sense to split also this patch into few more pieces that
> would remove the lock from a particular interface.
OK.
>> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
>> index e9018c4e1b66..7385101210be 100644
>> --- a/kernel/printk/printk.c
>> +++ b/kernel/printk/printk.c
>> @@ -785,7 +749,6 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
>> if (offset)
>> return -ESPIPE;
>>
>> - logbuf_lock_irq();
>
> user->seq manipulation is not longer safe from the atomicity point of
> view.
>
> One solution would be to use atomic variable in struct devkmsg_user().
> Another solution would be to synchronize it with user->lock like we do
> in devkmsg_read().
>
> user->lock looks like an overhead. But it actually would make sense to
> prevent seek in the middle of a read.
I would prefer using atomic64_t. Using user->lock could introduce some
wacky regression.
>> switch (whence) {
>> case SEEK_SET:
>> /* the first record */
>> @@ -820,7 +782,6 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
>>
>> poll_wait(file, &log_wait, wait);
>>
>> - logbuf_lock_irq();
>> if (prb_read_valid(prb, user->seq, NULL)) {
>
> Same here. The atomicity of user->seq read/write is not guaranteed.
Right.
John Ogness
next prev parent reply other threads:[~2020-12-06 20:52 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-01 20:53 [PATCH next v2 0/3] printk: remove logbuf_lock John Ogness
2020-12-01 20:53 ` [PATCH next v2 1/3] printk: inline log_output(),log_store() in vprintk_store() John Ogness
2020-12-03 15:57 ` Petr Mladek
2020-12-03 16:25 ` John Ogness
2020-12-04 6:13 ` Sergey Senozhatsky
2020-12-04 8:26 ` Petr Mladek
2020-12-01 20:53 ` [PATCH next v2 2/3] printk: change @clear_seq to atomic64_t John Ogness
2020-12-04 9:12 ` Petr Mladek
2020-12-06 20:23 ` John Ogness
2020-12-07 9:34 ` Peter Zijlstra
2020-12-07 10:03 ` John Ogness
2020-12-07 12:56 ` Peter Zijlstra
2020-12-07 12:56 ` Petr Mladek
2020-12-07 16:46 ` David Laight
2020-12-08 20:34 ` Sergey Senozhatsky
2020-12-08 22:30 ` John Ogness
2020-12-09 1:04 ` Sergey Senozhatsky
2020-12-09 8:16 ` Peter Zijlstra
2020-12-09 9:22 ` Sergey Senozhatsky
2020-12-09 10:46 ` Sergey Senozhatsky
2020-12-09 11:00 ` Peter Zijlstra
2020-12-09 11:28 ` Sergey Senozhatsky
2020-12-09 12:29 ` Peter Zijlstra
2020-12-09 8:07 ` Peter Zijlstra
2020-12-01 20:53 ` [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog_lock John Ogness
2020-12-04 6:41 ` Sergey Senozhatsky
2020-12-06 20:44 ` John Ogness
2020-12-04 15:52 ` devkmsg: was " Petr Mladek
2020-12-06 20:51 ` John Ogness [this message]
2020-12-07 9:56 ` Petr Mladek
2020-12-04 15:57 ` syslog: was: " Petr Mladek
2020-12-06 21:06 ` John Ogness
2020-12-07 10:01 ` Petr Mladek
2020-12-04 16:10 ` recursion handling: " Petr Mladek
2020-12-05 4:25 ` Sergey Senozhatsky
2020-12-06 22:08 ` John Ogness
2020-12-05 9:41 ` Sergey Senozhatsky
2020-12-06 22:17 ` John Ogness
2020-12-06 21:44 ` John Ogness
2020-12-07 11:17 ` Petr Mladek
2020-12-04 16:15 ` vprintk_store: was: " Petr Mladek
2020-12-06 22:30 ` John Ogness
2020-12-07 12:46 ` Petr Mladek
2020-12-04 16:19 ` consoles: " Petr Mladek
2020-12-05 4:39 ` Sergey Senozhatsky
2020-12-07 9:50 ` Petr Mladek
2020-12-08 20:51 ` Sergey Senozhatsky
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