linux-kernel - Re: recursion handling: Re: [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog

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Message-ID: <87mtyqmvf1.fsf@jogness.linutronix.de>
Date:   Sun, 06 Dec 2020 23:23:22 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: recursion handling: Re: [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog_lock

On 2020-12-05, Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:
>> One reason is the use of per-cpu variables. Alternative solution would
>> be to store printk_context into task_struct.
>
> We can keep per-CPU, disable preemption and have counters for
> every context (task, soft/hard irq, NMI). Shouldn't be a problem

These contexts are difficult to track correctly for all the preemption
models (especially when PREEMPT_RT is included). But I will look into
this idea. It would be nice to keep interrupts enabled for that first
vsnprintf() in vprintk_store().

John Ogness