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printk: nbcon: Init @nbcon_seq to highest possible

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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 <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240904120536.115780-6-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>
This commit is contained in:
John Ogness 2024-09-04 14:11:24 +02:06 committed by Petr Mladek
parent 6cb58cfebb
commit fb9fabf3d8
2 changed files with 9 additions and 1 deletions
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8
kernel/printk/nbcon.c
View File

@ -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) {
/*

2
kernel/printk/printk_ringbuffer.h
View File

@ -404,10 +404,12 @@ u64 prb_next_reserve_seq(struct printk_ringbuffer *rb);
#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)
{