From ad56ebd1d79b216dc147474fac89a11daf6b10df Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 16 Sep 2023 21:26:05 +0206 Subject: printk: nbcon: Add sequence handling Add an atomic_long_t field @nbcon_seq to the console struct to store the sequence number for nbcon consoles. For nbcon consoles this will be used instead of the non-atomic @seq field. The new field allows for safe atomic sequence number updates without requiring any locking. On 64bit systems the new field stores the full sequence number. On 32bit systems the new field stores the lower 32 bits of the sequence number, which are expanded to 64bit as needed by folding the values based on the sequence numbers available in the ringbuffer. For 32bit systems, having a 32bit representation in the console is sufficient. If a console ever gets more than 2^31 records behind the ringbuffer then this is the least of the problems. Co-developed-by: John Ogness Signed-off-by: John Ogness Signed-off-by: Thomas Gleixner (Intel) Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20230916192007.608398-7-john.ogness@linutronix.de --- kernel/printk/printk.c | 31 ++++++++++++++++++++++++------- 1 file changed, 24 insertions(+), 7 deletions(-) (limited to 'kernel/printk/printk.c') diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 1c9720acd960..77857d2118ca 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -494,7 +494,7 @@ _DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS, static struct printk_ringbuffer printk_rb_dynamic; -static struct printk_ringbuffer *prb = &printk_rb_static; +struct printk_ringbuffer *prb = &printk_rb_static; /* * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before @@ -3168,6 +3168,7 @@ void console_flush_on_panic(enum con_flush_mode mode) if (mode == CONSOLE_REPLAY_ALL) { struct console *c; + short flags; int cookie; u64 seq; @@ -3175,11 +3176,17 @@ void console_flush_on_panic(enum con_flush_mode mode) cookie = console_srcu_read_lock(); for_each_console_srcu(c) { - /* - * This is an unsynchronized assignment, but the - * kernel is in "hope and pray" mode anyway. - */ - c->seq = seq; + flags = console_srcu_read_flags(c); + + if (flags & CON_NBCON) { + nbcon_seq_force(c, seq); + } else { + /* + * This is an unsynchronized assignment. On + * panic legacy consoles are only best effort. + */ + c->seq = seq; + } } console_srcu_read_unlock(cookie); } @@ -3750,6 +3757,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre struct console *c; u64 last_diff = 0; u64 printk_seq; + short flags; int cookie; u64 diff; u64 seq; @@ -3771,6 +3779,9 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre for_each_console_srcu(c) { if (con && con != c) continue; + + flags = console_srcu_read_flags(c); + /* * If consoles are not usable, it cannot be expected * that they make forward progress, so only increment @@ -3778,7 +3789,13 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre */ if (!console_is_usable(c)) continue; - printk_seq = c->seq; + + if (flags & CON_NBCON) { + printk_seq = nbcon_seq_read(c); + } else { + printk_seq = c->seq; + } + if (printk_seq < seq) diff += seq - printk_seq; } -- cgit v1.2.3