linux-kernel - Re: synchronization model: was: Re: [PATCH printk-rework 09/14] printk: introduce a kmsg

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Message-ID: <877dmvxm2i.fsf@jogness.linutronix.de>
Date:   Fri, 26 Feb 2021 09:36:21 +0100
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: synchronization model: was: Re: [PATCH printk-rework 09/14] printk: introduce a kmsg_dump iterator

On 2021-02-25, Petr Mladek <pmladek@...e.com> wrote:
> IMHO, a better design would be:
>
> 1. dumper->dump() callback should have only one parameter @reason.
>    The callback should define its own iterator, buffer, and
>    do the dump.

Unfortunately this won't work because drivers/mtd/mtdoops.c is using the
dumper parameter for container_of().

So we will need 2 parameters: dumper and reason.

Can we agree to proceed with 2 parameters in the callback?

> 2. dumpe->dump() callback should synchronize the entire operation
>    using its own locks. Only the callback knows whether it is
>    safe to do more dumps in parallel. Only the callback knows
>    whether it is called only during panic() when no locks
>    are needed.

Agreed. I implemented this part for the v3 series.

John Ogness