From: Petr Mladek Date: Tue, 20 Aug 2024 08:35:29 +0206 Subject: [PATCH 03/54] printk: Properly deal with nbcon consoles on seq init Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.11/older/patches-6.11-rt7.tar.xz If a non-boot console is registering and boot consoles exist, the consoles are flushed before being unregistered. This allows the non-boot console to continue where the boot console left off. If for whatever reason flushing fails, the lowest seq found from any of the enabled boot consoles is used. Until now con->seq was checked. However, if it is an nbcon boot console, the function nbcon_seq_read() must be used to read seq because con->seq is not updated for nbcon consoles. Check if it is an nbcon boot console and if so call nbcon_seq_read() to read seq. Also, avoid usage of con->seq as temporary storage of the starting record. Instead, rename console_init_seq() to get_init_console_seq() and just return the value. For nbcon consoles set the sequence via nbcon_seq_force(), for legacy consoles set con->seq. The cleaned design should make sure that the value stays and is set before the console is added to the console list. It also unifies the sequence number initialization for legacy and nbcon consoles. Reviewed-by: John Ogness Link: https://lore.kernel.org/r/20240820063001.36405-4-john.ogness@linutronix.de Signed-off-by: Petr Mladek Signed-off-by: Sebastian Andrzej Siewior --- kernel/printk/nbcon.c | 3 --- kernel/printk/printk.c | 41 +++++++++++++++++++++++++++++------------ 2 files changed, 29 insertions(+), 15 deletions(-) --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -172,9 +172,6 @@ void nbcon_seq_force(struct console *con u64 valid_seq = max_t(u64, seq, prb_first_valid_seq(prb)); atomic_long_set(&ACCESS_PRIVATE(con, nbcon_seq), __u64seq_to_ulseq(valid_seq)); - - /* Clear con->seq since nbcon consoles use con->nbcon_seq instead. */ - con->seq = 0; } /** --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3449,19 +3449,21 @@ static void try_enable_default_console(s newcon->flags |= CON_CONSDEV; } -static void console_init_seq(struct console *newcon, bool bootcon_registered) +/* Return the starting sequence number for a newly registered console. */ +static u64 get_init_console_seq(struct console *newcon, bool bootcon_registered) { struct console *con; bool handover; + u64 init_seq; if (newcon->flags & (CON_PRINTBUFFER | CON_BOOT)) { /* Get a consistent copy of @syslog_seq. */ mutex_lock(&syslog_lock); - newcon->seq = syslog_seq; + init_seq = syslog_seq; mutex_unlock(&syslog_lock); } else { /* Begin with next message added to ringbuffer. */ - newcon->seq = prb_next_seq(prb); + init_seq = prb_next_seq(prb); /* * If any enabled boot consoles are due to be unregistered @@ -3482,7 +3484,7 @@ static void console_init_seq(struct cons * Flush all consoles and set the console to start at * the next unprinted sequence number. */ - if (!console_flush_all(true, &newcon->seq, &handover)) { + if (!console_flush_all(true, &init_seq, &handover)) { /* * Flushing failed. Just choose the lowest * sequence of the enabled boot consoles. @@ -3495,19 +3497,30 @@ static void console_init_seq(struct cons if (handover) console_lock(); - newcon->seq = prb_next_seq(prb); + init_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; + u64 seq; + + if (!(con->flags & CON_BOOT) || + !(con->flags & CON_ENABLED)) { + continue; } + + if (con->flags & CON_NBCON) + seq = nbcon_seq_read(con); + else + seq = con->seq; + + if (seq < init_seq) + init_seq = seq; } } console_unlock(); } } + + return init_seq; } #define console_first() \ @@ -3539,6 +3552,7 @@ void register_console(struct console *ne struct console *con; bool bootcon_registered = false; bool realcon_registered = false; + u64 init_seq; int err; console_list_lock(); @@ -3616,10 +3630,13 @@ void register_console(struct console *ne } newcon->dropped = 0; - console_init_seq(newcon, bootcon_registered); + init_seq = get_init_console_seq(newcon, bootcon_registered); - if (newcon->flags & CON_NBCON) - nbcon_seq_force(newcon, newcon->seq); + if (newcon->flags & CON_NBCON) { + nbcon_seq_force(newcon, init_seq); + } else { + newcon->seq = init_seq; + } /* * Put this console in the list - keep the