From: John Ogness Date: Wed, 4 Sep 2024 14:11:24 +0206 Subject: [PATCH 42/54] printk: nbcon: Init @nbcon_seq to highest possible Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.11/older/patches-6.11-rt7.tar.xz When initializing an nbcon console, have nbcon_alloc() set @nbcon_seq to the highest possible sequence number. For all practical purposes, this will guarantee that the console will have nothing to print until later when @nbcon_seq is set to the proper initial printing value. This will be particularly important once kthread printing is introduced because nbcon_alloc() can create/start the kthread before the desired initial sequence number is known. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Link: https://lore.kernel.org/r/20240904120536.115780-6-john.ogness@linutronix.de Signed-off-by: Petr Mladek Signed-off-by: Sebastian Andrzej Siewior --- kernel/printk/nbcon.c | 8 +++++++- kernel/printk/printk_ringbuffer.h | 2 ++ 2 files changed, 9 insertions(+), 1 deletion(-) --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -1397,7 +1397,13 @@ bool nbcon_alloc(struct console *con) struct nbcon_state state = { }; nbcon_state_set(con, &state); - atomic_long_set(&ACCESS_PRIVATE(con, nbcon_seq), 0); + + /* + * Initialize @nbcon_seq to the highest possible sequence number so + * that practically speaking it will have nothing to print until a + * desired initial sequence number has been set via nbcon_seq_force(). + */ + atomic_long_set(&ACCESS_PRIVATE(con, nbcon_seq), ULSEQ_MAX(prb)); if (con->flags & CON_BOOT) { /* --- a/kernel/printk/printk_ringbuffer.h +++ b/kernel/printk/printk_ringbuffer.h @@ -404,10 +404,12 @@ u64 prb_next_reserve_seq(struct printk_r #define __u64seq_to_ulseq(u64seq) (u64seq) #define __ulseq_to_u64seq(rb, ulseq) (ulseq) +#define ULSEQ_MAX(rb) (-1) #else /* CONFIG_64BIT */ #define __u64seq_to_ulseq(u64seq) ((u32)u64seq) +#define ULSEQ_MAX(rb) __u64seq_to_ulseq(prb_first_seq(rb) + 0x80000000UL) static inline u64 __ulseq_to_u64seq(struct printk_ringbuffer *rb, u32 ulseq) {