Re: replay log: Re: [PATCH printk v4 38/39] printk: relieve console_lock of list synchronization duties

From: John Ogness
Date: Wed Nov 16 2022 - 04:09:40 EST


Hi Petr,

Sorry, console_flush_all() only loses the console_lock if there was a
handover. Here is a new complete suggestion from me.

if (newcon->flags & (CON_PRINTBUFFER | CON_BOOT)) {
/* Get a consistent copy of @syslog_seq. */
mutex_lock(&syslog_lock);
newcon->seq = syslog_seq;
mutex_unlock(&syslog_lock);
} else {
/* Begin with next message added to ringbuffer. */
newcon->seq = prb_next_seq(prb);

/*
* If any enabled boot consoles are due to be unregistered
* shortly, some may not be caught up and may be the same
* device as @newcon. Since it is not known which boot console
* is the same device, flush all consoles and, if necessary,
* start with the message of the enabled boot console that is
* the furthest behind.
*/
if (bootcon_registered && !keep_bootcon) {
bool handover;

/*
* Hold the console_lock to guarantee safe access to
* console->seq.
*/
console_lock();

/*
* Flush all consoles and set the console to start at
* the next unprinted sequence number.
*/
if (!console_flush_all(true, &newcon->seq, &handover)) {
/*
* Flushing failed. Just choose the lowest
* sequence of the enabled boot consoles.
*/

/*
* If there was a handover, this context no
* longer holds the console_lock.
*/
if (handover)
console_lock();

newcon->seq = prb_next_seq(prb);
for_each_console(con) {
if ((con->flags & CON_BOOT) &&
(con->flags & CON_ENABLED) &&
con->seq < newcon->seq) {
newcon->seq = con->seq;
}
}
}

console_unlock();
}

John Ogness