linux-kernel - Re: [PATCH] printk: Enough to disable preemption in printk deferred context

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Message-ID: <20230419082311.GA1496740@google.com>
Date:   Wed, 19 Apr 2023 17:23:11 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] printk: Enough to disable preemption in printk deferred
 context

On (23/04/19 09:42), Petr Mladek wrote:
> The comment above printk_deferred_enter()/exit() definition claims
> that it can be used only when interrupts are disabled.
> 
> It was required by the original printk_safe_log_store() implementation.
> The code provided lockless synchronization between a single writer and
> a single reader. The interrupt and the normal context shared the same
> buffer.
> 
> The commit 93d102f094be ("printk: remove safe buffers") removed
> these temporary buffers. Instead, the messages are stored directly into
> the new global lockless buffer which supports multiple parallel writers.
> 
> As a result, it is safe to interrupt one writer now. The preemption still
> has to be disabled because the deferred context is CPU specific.
> 
> Fixes: 93d102f094be ("printk: remove safe buffers")
> Signed-off-by: Petr Mladek <pmladek@...e.com>

Looks good to me

Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>