From: Petr Mladek <pmladek@suse.com> Date: Wed, 22 Nov 2023 11:23:43 +0000 Subject: [PATCH 02/46] printk: Properly deal with nbcon consoles on seq init 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_init(), for legacy consoles set con->seq. The cleaned design should make sure that the value stays and is set before the printing kthread is created. Signed-off-by: Petr Mladek <pmladek@suse.com> Reviewed-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- kernel/printk/internal.h | 4 ++-- kernel/printk/nbcon.c | 10 +++------- kernel/printk/printk.c | 41 +++++++++++++++++++++++++++++------------ 3 files changed, 34 insertions(+), 21 deletions(-) @ kernel/printk/internal.h:78 @ u16 printk_parse_prefix(const char *text u64 nbcon_seq_read(struct console *con); void nbcon_seq_force(struct console *con, u64 seq); bool nbcon_alloc(struct console *con); -void nbcon_init(struct console *con); +void nbcon_init(struct console *con, u64 init_seq); void nbcon_free(struct console *con); #else @ kernel/printk/internal.h:99 @ static inline bool printk_percpu_data_re static inline u64 nbcon_seq_read(struct console *con) { return 0; } static inline void nbcon_seq_force(struct console *con, u64 seq) { } static inline bool nbcon_alloc(struct console *con) { return false; } -static inline void nbcon_init(struct console *con) { } +static inline void nbcon_init(struct console *con, u64 init_seq) { } static inline void nbcon_free(struct console *con) { } #endif /* CONFIG_PRINTK */ --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @ kernel/printk/internal.h:175 @ 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; } /** @ kernel/printk/internal.h:961 @ bool nbcon_alloc(struct console *con) /** * nbcon_init - Initialize the nbcon console specific data * @con: Console to initialize + * @init_seq: Sequence number of the first record to be emitted * * nbcon_alloc() *must* be called and succeed before this function * is called. - * - * This function expects that the legacy @con->seq has been set. */ -void nbcon_init(struct console *con) +void nbcon_init(struct console *con, u64 init_seq) { struct nbcon_state state = { }; /* nbcon_alloc() must have been called and successful! */ BUG_ON(!con->pbufs); - nbcon_seq_force(con, con->seq); + nbcon_seq_force(con, init_seq); nbcon_state_set(con, &state); } --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @ kernel/printk/internal.h:3366 @ 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 @ kernel/printk/internal.h:3401 @ 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. @ kernel/printk/internal.h:3414 @ 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() \ @ kernel/printk/internal.h:3469 @ 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(); @ kernel/printk/internal.h:3547 @ 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_init(newcon); + if (newcon->flags & CON_NBCON) { + nbcon_init(newcon, init_seq); + } else { + newcon->seq = init_seq; + } /* * Put this console in the list - keep the