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SubjectRe: [PATCH printk v3 6/6] printk: syslog: close window between wait and read
On Thu, 24 Jun 2021 13:17:48 +0206
John Ogness <john.ogness@linutronix.de> wrote:

> + * @syslog_lock is held when entering the read loop to prevent
> + * another reader from modifying @syslog_seq.

You should add to the above comment:

* And the @syslog_lock is released before exiting the loop.

Because it's not normal to enter a loop locked, and have it unlocked
when exiting the loop. And I can envision in the future, someone might
add a break (for error) while still holding the lock.

-- Steve

> + */
> +
> + for (;;) {
> size_t n;
> size_t skip;
>
> - mutex_lock(&syslog_lock);
> if (!prb_read_valid(prb, syslog_seq, &r)) {
> mutex_unlock(&syslog_lock);
> break;
> @@ -1542,8 +1570,13 @@ static int syslog_print(char __user *buf, int size)
> len += n;
> size -= n;
> buf += n;
> - }
>
> + if (!size)
> + break;
> +
> + mutex_lock(&syslog_lock);
> + }

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