From: John Ogness Date: Tue, 20 Aug 2024 08:35:52 +0206 Subject: [PATCH 26/54] printk: nbcon: Add unsafe flushing on panic Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.11/older/patches-6.11-rt7.tar.xz Add nbcon_atomic_flush_unsafe() to flush all nbcon consoles using the write_atomic() callback and allowing unsafe hostile takeovers. Call this at the end of panic() as a final attempt to flush any pending messages. Note that legacy consoles use unsafe methods for flushing from the beginning of panic (see bust_spinlocks()). Therefore, systems using both legacy and nbcon consoles may still fail to see panic messages due to unsafe legacy console usage. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Link: https://lore.kernel.org/r/20240820063001.36405-27-john.ogness@linutronix.de Signed-off-by: Petr Mladek Signed-off-by: Sebastian Andrzej Siewior --- include/linux/printk.h | 5 +++++ kernel/panic.c | 1 + kernel/printk/nbcon.c | 32 +++++++++++++++++++++++++------- 3 files changed, 31 insertions(+), 7 deletions(-) --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -202,6 +202,7 @@ void printk_trigger_flush(void); void console_try_replay_all(void); extern bool nbcon_device_try_acquire(struct console *con); extern void nbcon_device_release(struct console *con); +void nbcon_atomic_flush_unsafe(void); #else static inline __printf(1, 0) int vprintk(const char *s, va_list args) @@ -294,6 +295,10 @@ static inline void nbcon_device_release( { } +static inline void nbcon_atomic_flush_unsafe(void) +{ +} + #endif bool this_cpu_in_panic(void); --- a/kernel/panic.c +++ b/kernel/panic.c @@ -463,6 +463,7 @@ void panic(const char *fmt, ...) * Explicitly flush the kernel log buffer one last time. */ console_flush_on_panic(CONSOLE_FLUSH_PENDING); + nbcon_atomic_flush_unsafe(); local_irq_enable(); for (i = 0; ; i += PANIC_TIMER_STEP) { --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -1083,6 +1083,7 @@ bool nbcon_legacy_emit_next_record(struc * write_atomic() callback * @con: The nbcon console to flush * @stop_seq: Flush up until this record + * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers * * Return: 0 if @con was flushed up to @stop_seq Otherwise, error code on * failure. @@ -1101,7 +1102,8 @@ bool nbcon_legacy_emit_next_record(struc * returned, it cannot be expected that the unfinalized record will become * available. */ -static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq) +static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq, + bool allow_unsafe_takeover) { struct nbcon_write_context wctxt = { }; struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt); @@ -1110,6 +1112,7 @@ static int __nbcon_atomic_flush_pending_ ctxt->console = con; ctxt->spinwait_max_us = 2000; ctxt->prio = nbcon_get_default_prio(); + ctxt->allow_unsafe_takeover = allow_unsafe_takeover; if (!nbcon_context_try_acquire(ctxt)) return -EPERM; @@ -1140,13 +1143,15 @@ static int __nbcon_atomic_flush_pending_ * write_atomic() callback * @con: The nbcon console to flush * @stop_seq: Flush up until this record + * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers * * This will stop flushing before @stop_seq if another context has ownership. * That context is then responsible for the flushing. Likewise, if new records * are added while this context was flushing and there is no other context * to handle the printing, this context must also flush those records. */ -static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq) +static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq, + bool allow_unsafe_takeover) { unsigned long flags; int err; @@ -1160,7 +1165,7 @@ static void nbcon_atomic_flush_pending_c */ local_irq_save(flags); - err = __nbcon_atomic_flush_pending_con(con, stop_seq); + err = __nbcon_atomic_flush_pending_con(con, stop_seq, allow_unsafe_takeover); local_irq_restore(flags); @@ -1190,8 +1195,9 @@ static void nbcon_atomic_flush_pending_c * __nbcon_atomic_flush_pending - Flush all nbcon consoles using their * write_atomic() callback * @stop_seq: Flush up until this record + * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers */ -static void __nbcon_atomic_flush_pending(u64 stop_seq) +static void __nbcon_atomic_flush_pending(u64 stop_seq, bool allow_unsafe_takeover) { struct console *con; int cookie; @@ -1209,7 +1215,7 @@ static void __nbcon_atomic_flush_pending if (nbcon_seq_read(con) >= stop_seq) continue; - nbcon_atomic_flush_pending_con(con, stop_seq); + nbcon_atomic_flush_pending_con(con, stop_seq, allow_unsafe_takeover); } console_srcu_read_unlock(cookie); } @@ -1225,7 +1231,19 @@ static void __nbcon_atomic_flush_pending */ void nbcon_atomic_flush_pending(void) { - __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb)); + __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb), false); +} + +/** + * nbcon_atomic_flush_unsafe - Flush all nbcon consoles using their + * write_atomic() callback and allowing unsafe hostile takeovers + * + * Flush the backlog up through the currently newest record. Unsafe hostile + * takeovers will be performed, if necessary. + */ +void nbcon_atomic_flush_unsafe(void) +{ + __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb), true); } /** @@ -1342,7 +1360,7 @@ void nbcon_device_release(struct console if (console_is_usable(con, console_srcu_read_flags(con)) && prb_read_valid(prb, nbcon_seq_read(con), NULL)) { if (!have_boot_console) { - __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb)); + __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb), false); } else if (!is_printk_legacy_deferred()) { if (console_trylock()) console_unlock();