diff options
Diffstat (limited to 'debian/patches-rt/0020-printk-nbcon-Provide-function-to-flush-using-write_a.patch')
| -rw-r--r-- | debian/patches-rt/0020-printk-nbcon-Provide-function-to-flush-using-write_a.patch | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/debian/patches-rt/0020-printk-nbcon-Provide-function-to-flush-using-write_a.patch b/debian/patches-rt/0020-printk-nbcon-Provide-function-to-flush-using-write_a.patch new file mode 100644 index 0000000000..26c68ed229 --- /dev/null +++ b/debian/patches-rt/0020-printk-nbcon-Provide-function-to-flush-using-write_a.patch @@ -0,0 +1,193 @@ +From: Thomas Gleixner <tglx@linutronix.de> +Date: Tue, 12 Sep 2023 12:00:08 +0000 +Subject: [PATCH 20/48] printk: nbcon: Provide function to flush using + write_atomic() +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.8/older/patches-6.8.2-rt11.tar.xz + +Provide nbcon_atomic_flush_pending() to perform flushing of all +registered nbcon consoles using their write_atomic() callback. + +Unlike console_flush_all(), nbcon_atomic_flush_pending() will +only flush up through the newest record at the time of the +call. This prevents a CPU from printing unbounded when other +CPUs are adding records. + +Also unlike console_flush_all(), nbcon_atomic_flush_pending() +will fully flush one console before flushing the next. This +helps to guarantee that a block of pending records (such as +a stack trace in an emergency situation) can be printed +atomically at once before releasing console ownership. + +nbcon_atomic_flush_pending() is safe in any context because it +uses write_atomic() and acquires with unsafe_takeover disabled. + +Use it in console_flush_on_panic() before flushing legacy +consoles. The legacy write() callbacks are not fully safe when +oops_in_progress is set. + +Co-developed-by: John Ogness <john.ogness@linutronix.de> +Signed-off-by: John Ogness <john.ogness@linutronix.de> +Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/printk/internal.h | 2 + kernel/printk/nbcon.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++- + kernel/printk/printk.c | 2 + 3 files changed, 106 insertions(+), 2 deletions(-) + +--- a/kernel/printk/internal.h ++++ b/kernel/printk/internal.h +@@ -84,6 +84,7 @@ void nbcon_seq_force(struct console *con + bool nbcon_alloc(struct console *con); + void nbcon_init(struct console *con); + void nbcon_free(struct console *con); ++void nbcon_atomic_flush_pending(void); + + /* + * Check if the given console is currently capable and allowed to print +@@ -138,6 +139,7 @@ static inline void nbcon_seq_force(struc + static inline bool nbcon_alloc(struct console *con) { return false; } + static inline void nbcon_init(struct console *con) { } + static inline void nbcon_free(struct console *con) { } ++static inline void nbcon_atomic_flush_pending(void) { } + + static inline bool console_is_usable(struct console *con, short flags) { return false; } + +--- a/kernel/printk/nbcon.c ++++ b/kernel/printk/nbcon.c +@@ -548,7 +548,6 @@ static struct printk_buffers panic_nbcon + * in an unsafe state. Otherwise, on success the caller may assume + * the console is not in an unsafe state. + */ +-__maybe_unused + static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) + { + unsigned int cpu = smp_processor_id(); +@@ -850,7 +849,6 @@ EXPORT_SYMBOL_GPL(nbcon_exit_unsafe); + * When true is returned, @wctxt->ctxt.backlog indicates whether there are + * still records pending in the ringbuffer, + */ +-__maybe_unused + static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt) + { + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); +@@ -938,6 +936,108 @@ static bool nbcon_emit_next_record(struc + } + + /** ++ * __nbcon_atomic_flush_pending_con - Flush specified nbcon console using its ++ * write_atomic() callback ++ * @con: The nbcon console to flush ++ * @stop_seq: Flush up until this record ++ * ++ * Return: True if taken over while printing. Otherwise false. ++ * ++ * If flushing up to @stop_seq was not successful, it only makes sense for the ++ * caller to try again when true was returned. When false is returned, either ++ * there are no more records available to read or this context is not allowed ++ * to acquire the console. ++ */ ++static bool __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq) ++{ ++ struct nbcon_write_context wctxt = { }; ++ struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt); ++ ++ ctxt->console = con; ++ ctxt->spinwait_max_us = 2000; ++ ctxt->prio = NBCON_PRIO_NORMAL; ++ ++ if (!nbcon_context_try_acquire(ctxt)) ++ return false; ++ ++ while (nbcon_seq_read(con) < stop_seq) { ++ /* ++ * nbcon_emit_next_record() returns false when the console was ++ * handed over or taken over. In both cases the context is no ++ * longer valid. ++ */ ++ if (!nbcon_emit_next_record(&wctxt)) ++ return true; ++ ++ if (!ctxt->backlog) ++ break; ++ } ++ ++ nbcon_context_release(ctxt); ++ ++ return false; ++} ++ ++/** ++ * __nbcon_atomic_flush_pending - Flush all nbcon consoles using their ++ * write_atomic() callback ++ * @stop_seq: Flush up until this record ++ */ ++static void __nbcon_atomic_flush_pending(u64 stop_seq) ++{ ++ struct console *con; ++ bool should_retry; ++ int cookie; ++ ++ do { ++ should_retry = false; ++ ++ cookie = console_srcu_read_lock(); ++ for_each_console_srcu(con) { ++ short flags = console_srcu_read_flags(con); ++ unsigned long irq_flags; ++ ++ if (!(flags & CON_NBCON)) ++ continue; ++ ++ if (!console_is_usable(con, flags)) ++ continue; ++ ++ if (nbcon_seq_read(con) >= stop_seq) ++ continue; ++ ++ /* ++ * Atomic flushing does not use console driver ++ * synchronization (i.e. it does not hold the port ++ * lock for uart consoles). Therefore IRQs must be ++ * disabled to avoid being interrupted and then ++ * calling into a driver that will deadlock trying ++ * to acquire console ownership. ++ */ ++ local_irq_save(irq_flags); ++ ++ should_retry |= __nbcon_atomic_flush_pending_con(con, stop_seq); ++ ++ local_irq_restore(irq_flags); ++ } ++ console_srcu_read_unlock(cookie); ++ } while (should_retry); ++} ++ ++/** ++ * nbcon_atomic_flush_pending - Flush all nbcon consoles using their ++ * write_atomic() callback ++ * ++ * Flush the backlog up through the currently newest record. Any new ++ * records added while flushing will not be flushed. This is to avoid ++ * one CPU printing unbounded because other CPUs continue to add records. ++ */ ++void nbcon_atomic_flush_pending(void) ++{ ++ __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb)); ++} ++ ++/** + * nbcon_alloc - Allocate buffers needed by the nbcon console + * @con: Console to allocate buffers for + * +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -3177,6 +3177,8 @@ void console_flush_on_panic(enum con_flu + console_srcu_read_unlock(cookie); + } + ++ nbcon_atomic_flush_pending(); ++ + console_flush_all(false, &next_seq, &handover); + } + |