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From:   John Ogness <john.ogness@linutronix.de>
To:     Petr Mladek <pmladek@suse.com>
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 02/25] printk-rb: add prb locking functions
References: <20190212143003.48446-1-john.ogness@linutronix.de>
        <20190212143003.48446-3-john.ogness@linutronix.de>
        <20190213154541.wvft64nf352vghou@pathway.suse.cz>
        <87pnrvs707.fsf@linutronix.de>
        <20190214103324.viexpifsyons5qya@pathway.suse.cz>
        <87y36ih8p7.fsf@linutronix.de>
        <20190215102635.kdo4yxifh5dt2yj7@pathway.suse.cz>
Date:   Fri, 15 Feb 2019 11:56:15 +0100
In-Reply-To: <20190215102635.kdo4yxifh5dt2yj7@pathway.suse.cz> (Petr Mladek's
        message of "Fri, 15 Feb 2019 11:26:35 +0100")
Message-ID: <87y36hials.fsf@linutronix.de>
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On 2019-02-15, Petr Mladek <pmladek@suse.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