linux-kernel - Re: [PATCH printk v4 6/6] printk: syslog: close window between wait and read

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Message-ID: <20210721124319.hy5rrn6p2i2r2qya@pathway.suse.cz>
Date:   Wed, 21 Jul 2021 14:43:19 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk v4 6/6] printk: syslog: close window between wait
 and read

On Thu 2021-07-15 21:39:59, John Ogness wrote:
> Syslog's SYSLOG_ACTION_READ is supposed to block until the next
> syslog record can be read, and then it should read that record.
> However, because @syslog_lock is not held between waking up and
> reading the record, another reader could read the record first,
> thus causing SYSLOG_ACTION_READ to return with a value of 0, never
> having read _anything_.
> 
> By holding @syslog_lock between waking up and reading, it can be
> guaranteed that SYSLOG_ACTION_READ blocks until it successfully
> reads a syslog record (or a real error occurs).
> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr