diff options
Diffstat (limited to 'debian/patches-rt/0018-printk-nbcon-Provide-function-to-flush-using-write_a.patch')
| -rw-r--r-- | debian/patches-rt/0018-printk-nbcon-Provide-function-to-flush-using-write_a.patch | 260 |
1 files changed, 260 insertions, 0 deletions
diff --git a/debian/patches-rt/0018-printk-nbcon-Provide-function-to-flush-using-write_a.patch b/debian/patches-rt/0018-printk-nbcon-Provide-function-to-flush-using-write_a.patch new file mode 100644 index 0000000000..b42d8623bb --- /dev/null +++ b/debian/patches-rt/0018-printk-nbcon-Provide-function-to-flush-using-write_a.patch @@ -0,0 +1,260 @@ +From: Thomas Gleixner <tglx@linutronix.de> +Date: Tue, 12 Sep 2023 12:00:08 +0000 +Subject: [PATCH 18/46] printk: nbcon: Provide function to flush using + write_atomic() +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.9/older/patches-6.9-rt5.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. If new records are added while +flushing, it is expected that the dedicated printer threads +will print those records. If the printer thread is not +available (which is always the case at this point in the +rework), nbcon_atomic_flush_pending() _will_ flush all records +in the ringbuffer. + +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. + +Also use it in nbcon_driver_release() to flush records added +while the driver had the console locked to perform non-printing +operations. + +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 | 162 ++++++++++++++++++++++++++++++++++++++++++++++- + kernel/printk/printk.c | 2 + 3 files changed, 163 insertions(+), 3 deletions(-) + +--- a/kernel/printk/internal.h ++++ b/kernel/printk/internal.h +@@ -85,6 +85,7 @@ bool nbcon_alloc(struct console *con); + void nbcon_init(struct console *con, u64 init_seq); + void nbcon_free(struct console *con); + enum nbcon_prio nbcon_get_default_prio(void); ++void nbcon_atomic_flush_pending(void); + + /* + * Check if the given console is currently capable and allowed to print +@@ -140,6 +141,7 @@ static inline bool nbcon_alloc(struct co + static inline void nbcon_init(struct console *con, u64 init_seq) { } + static inline void nbcon_free(struct console *con) { } + static inline enum nbcon_prio nbcon_get_default_prio(void) { return NBCON_PRIO_NONE; } ++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 +@@ -850,7 +850,6 @@ 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); +@@ -953,6 +952,148 @@ enum nbcon_prio nbcon_get_default_prio(v + return NBCON_PRIO_NORMAL; + } + ++/* ++ * __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: 0 if @con was flushed up to @stop_seq Otherwise, error code on ++ * failure. ++ * ++ * Errors: ++ * ++ * -EPERM: Unable to acquire console ownership. ++ * ++ * -EAGAIN: Another context took over ownership while printing. ++ * ++ * -ENOENT: A record before @stop_seq is not available. ++ * ++ * If flushing up to @stop_seq was not successful, it only makes sense for the ++ * caller to try again when -EAGAIN was returned. When -EPERM is returned, ++ * this context is not allowed to acquire the console. When -ENOENT is ++ * 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) ++{ ++ struct nbcon_write_context wctxt = { }; ++ struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt); ++ int err = 0; ++ ++ ctxt->console = con; ++ ctxt->spinwait_max_us = 2000; ++ ctxt->prio = nbcon_get_default_prio(); ++ ++ if (!nbcon_context_try_acquire(ctxt)) ++ return -EPERM; ++ ++ 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 -EAGAIN; ++ ++ if (!ctxt->backlog) { ++ if (nbcon_seq_read(con) < stop_seq) ++ err = -ENOENT; ++ break; ++ } ++ } ++ ++ nbcon_context_release(ctxt); ++ return err; ++} ++ ++/** ++ * 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 ++ * ++ * 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) ++{ ++ unsigned long flags; ++ int err; ++ ++again: ++ /* ++ * 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(flags); ++ ++ err = __nbcon_atomic_flush_pending_con(con, stop_seq); ++ ++ local_irq_restore(flags); ++ ++ /* ++ * If flushing was successful but more records are available, this ++ * context must flush those remaining records because there is no ++ * other context that will do it. ++ */ ++ if (!err && prb_read_valid(prb, nbcon_seq_read(con), NULL)) { ++ stop_seq = prb_next_reserve_seq(prb); ++ goto again; ++ } ++ ++ /* ++ * If there was a new owner, that context is responsible for ++ * completing the flush. ++ */ ++} ++ ++/** ++ * __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; ++ int cookie; ++ ++ cookie = console_srcu_read_lock(); ++ for_each_console_srcu(con) { ++ short flags = console_srcu_read_flags(con); ++ ++ if (!(flags & CON_NBCON)) ++ continue; ++ ++ if (!console_is_usable(con, flags)) ++ continue; ++ ++ if (nbcon_seq_read(con) >= stop_seq) ++ continue; ++ ++ nbcon_atomic_flush_pending_con(con, stop_seq); ++ } ++ console_srcu_read_unlock(cookie); ++} ++ ++/** ++ * 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 +@@ -1064,8 +1205,23 @@ EXPORT_SYMBOL_GPL(nbcon_driver_try_acqui + void nbcon_driver_release(struct console *con) + { + struct nbcon_context *ctxt = &ACCESS_PRIVATE(con, nbcon_driver_ctxt); ++ int cookie; + +- if (nbcon_context_exit_unsafe(ctxt)) +- nbcon_context_release(ctxt); ++ if (!nbcon_context_exit_unsafe(ctxt)) ++ return; ++ ++ nbcon_context_release(ctxt); ++ ++ /* ++ * This context must flush any new records added while the console ++ * was locked. The console_srcu_read_lock must be taken to ensure ++ * the console is usable throughout flushing. ++ */ ++ cookie = console_srcu_read_lock(); ++ if (console_is_usable(con, console_srcu_read_flags(con)) && ++ prb_read_valid(prb, nbcon_seq_read(con), NULL)) { ++ __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb)); ++ } ++ console_srcu_read_unlock(cookie); + } + EXPORT_SYMBOL_GPL(nbcon_driver_release); +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -3172,6 +3172,8 @@ void console_flush_on_panic(enum con_flu + console_srcu_read_unlock(cookie); + } + ++ nbcon_atomic_flush_pending(); ++ + console_flush_all(false, &next_seq, &handover); + } + |