linux-kernel - Re: [RFC PATCH v1 02/25] printk-rb: add prb locking functions

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Date:   Fri, 15 Feb 2019 11:56:15 +0100
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Wang <wonderfly@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Peter Feiner <pfeiner@...gle.com>,
        linux-serial@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC PATCH v1 02/25] printk-rb: add prb locking functions

On 2019-02-15, Petr Mladek <pmladek@...e.com> wrote:
>>> void prb_lock(struct prb_cpulock *cpu_lock)
>>> {
>>> 	unsigned int flags;
>>> 	int cpu;
>> 
>> I added an explicit preempt_disable here:
>> 
>>         cpu = get_cpu();
>
> It is superfluous. Preemption is not possible when interrupts
> are disabled.

Interrupts are not necessarily disabled here. They get disabled later if
the lock needs to be taken (i.e. we are not nested).

John Ogness