diff options
Diffstat (limited to 'debian/patches-rt/0037-printk-nbcon-Introduce-printing-kthreads.patch')
| -rw-r--r-- | debian/patches-rt/0037-printk-nbcon-Introduce-printing-kthreads.patch | 441 |
1 files changed, 441 insertions, 0 deletions
diff --git a/debian/patches-rt/0037-printk-nbcon-Introduce-printing-kthreads.patch b/debian/patches-rt/0037-printk-nbcon-Introduce-printing-kthreads.patch new file mode 100644 index 0000000000..712f144bee --- /dev/null +++ b/debian/patches-rt/0037-printk-nbcon-Introduce-printing-kthreads.patch @@ -0,0 +1,441 @@ +From: Thomas Gleixner <tglx@linutronix.de> +Date: Fri, 22 Sep 2023 14:12:21 +0000 +Subject: [PATCH 37/50] printk: nbcon: Introduce printing kthreads +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.7/older/patches-6.7-rt6.tar.xz + +Provide the main implementation for running a printer kthread +per nbcon console that is takeover/handover aware. + +The main print function nbcon_emit_next_record() will generate +a warning if a task other than the dedicated printer thread +tries to print using write_thread(). + +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> +--- + include/linux/console.h | 8 ++ + kernel/printk/internal.h | 25 ++++++ + kernel/printk/nbcon.c | 188 ++++++++++++++++++++++++++++++++++++++++++++++- + kernel/printk/printk.c | 31 +++++++ + 4 files changed, 249 insertions(+), 3 deletions(-) + +--- a/include/linux/console.h ++++ b/include/linux/console.h +@@ -17,6 +17,7 @@ + #include <linux/atomic.h> + #include <linux/bits.h> + #include <linux/rculist.h> ++#include <linux/rcuwait.h> + #include <linux/types.h> + + struct vc_data; +@@ -303,12 +304,15 @@ struct nbcon_write_context { + * @node: hlist node for the console list + * + * @write_atomic: Write callback for atomic context ++ * @write_thread: Write callback for non-atomic context + * @driver_enter: Callback to begin synchronization with driver code + * @driver_exit: Callback to finish synchronization with driver code + * @nbcon_state: State for nbcon consoles + * @nbcon_seq: Sequence number of the next record for nbcon to print + * @pbufs: Pointer to nbcon private buffer + * @locked_port: True, if the port lock is locked by nbcon ++ * @kthread: Printer kthread for this console ++ * @rcuwait: RCU-safe wait object for @kthread waking + */ + struct console { + char name[16]; +@@ -332,12 +336,16 @@ struct console { + /* nbcon console specific members */ + bool (*write_atomic)(struct console *con, + struct nbcon_write_context *wctxt); ++ bool (*write_thread)(struct console *con, ++ struct nbcon_write_context *wctxt); + void (*driver_enter)(struct console *con, unsigned long *flags); + void (*driver_exit)(struct console *con, unsigned long flags); + atomic_t __private nbcon_state; + atomic_long_t __private nbcon_seq; + struct printk_buffers *pbufs; + bool locked_port; ++ struct task_struct *kthread; ++ struct rcuwait rcuwait; + }; + + #ifdef CONFIG_LOCKDEP +--- a/kernel/printk/internal.h ++++ b/kernel/printk/internal.h +@@ -92,6 +92,7 @@ void nbcon_free(struct console *con); + enum nbcon_prio nbcon_get_default_prio(void); + void nbcon_atomic_flush_all(void); + bool nbcon_atomic_emit_next_record(struct console *con, bool *handover, int cookie); ++void nbcon_kthread_create(struct console *con); + + /* + * Check if the given console is currently capable and allowed to print +@@ -110,6 +111,8 @@ static inline bool console_is_usable(str + if (flags & CON_NBCON) { + if (!con->write_atomic) + return false; ++ if (!con->write_thread || !con->kthread) ++ return false; + } else { + if (!con->write) + return false; +@@ -126,12 +129,34 @@ static inline bool console_is_usable(str + return true; + } + ++/** ++ * nbcon_kthread_wake - Wake up a printk thread ++ * @con: Console to operate on ++ */ ++static inline void nbcon_kthread_wake(struct console *con) ++{ ++ /* ++ * Guarantee any new records can be seen by tasks preparing to wait ++ * before this context checks if the rcuwait is empty. ++ * ++ * The full memory barrier in rcuwait_wake_up() pairs with the full ++ * memory barrier within set_current_state() of ++ * ___rcuwait_wait_event(), which is called after prepare_to_rcuwait() ++ * adds the waiter but before it has checked the wait condition. ++ * ++ * This pairs with nbcon_kthread_func:A. ++ */ ++ rcuwait_wake_up(&con->rcuwait); /* LMM(nbcon_kthread_wake:A) */ ++} ++ + #else + + #define PRINTK_PREFIX_MAX 0 + #define PRINTK_MESSAGE_MAX 0 + #define PRINTKRB_RECORD_MAX 0 + ++static inline void nbcon_kthread_wake(struct console *con) { } ++static inline void nbcon_kthread_create(struct console *con) { } + #define printing_via_unlock (false) + + /* +--- a/kernel/printk/nbcon.c ++++ b/kernel/printk/nbcon.c +@@ -5,8 +5,10 @@ + #include <linux/kernel.h> + #include <linux/console.h> + #include <linux/delay.h> ++#include <linux/kthread.h> + #include <linux/slab.h> + #include <linux/serial_core.h> ++#include "printk_ringbuffer.h" + #include "internal.h" + /* + * Printk console printing implementation for consoles which does not depend +@@ -828,6 +830,7 @@ EXPORT_SYMBOL_GPL(nbcon_exit_unsafe); + /** + * nbcon_emit_next_record - Emit a record in the acquired context + * @wctxt: The write context that will be handed to the write function ++ * @use_atomic: True if the write_atomic callback is to be used + * + * Return: True if this context still owns the console. False if + * ownership was handed over or taken. +@@ -841,7 +844,7 @@ EXPORT_SYMBOL_GPL(nbcon_exit_unsafe); + * When true is returned, @wctxt->ctxt.backlog indicates whether there are + * still records pending in the ringbuffer, + */ +-static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt) ++static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt, bool use_atomic) + { + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + struct console *con = ctxt->console; +@@ -891,9 +894,17 @@ static bool nbcon_emit_next_record(struc + nbcon_state_read(con, &cur); + wctxt->unsafe_takeover = cur.unsafe_takeover; + +- if (con->write_atomic) ++ if (use_atomic && ++ con->write_atomic) { + done = con->write_atomic(con, wctxt); + ++ } else if (!use_atomic && ++ con->write_thread && ++ con->kthread) { ++ WARN_ON_ONCE(con->kthread != current); ++ done = con->write_thread(con, wctxt); ++ } ++ + if (!done) { + /* + * The emit was aborted, probably due to a loss of ownership. +@@ -929,6 +940,118 @@ static bool nbcon_emit_next_record(struc + return nbcon_context_exit_unsafe(ctxt); + } + ++/** ++ * nbcon_kthread_should_wakeup - Check whether a printer thread should wakeup ++ * @con: Console to operate on ++ * @ctxt: The acquire context that contains the state ++ * at console_acquire() ++ * ++ * Return: True if the thread should shutdown or if the console is ++ * allowed to print and a record is available. False otherwise. ++ * ++ * After the thread wakes up, it must first check if it should shutdown before ++ * attempting any printing. ++ */ ++static bool nbcon_kthread_should_wakeup(struct console *con, struct nbcon_context *ctxt) ++{ ++ bool is_usable; ++ short flags; ++ int cookie; ++ ++ if (kthread_should_stop()) ++ return true; ++ ++ cookie = console_srcu_read_lock(); ++ flags = console_srcu_read_flags(con); ++ is_usable = console_is_usable(con, flags); ++ console_srcu_read_unlock(cookie); ++ ++ if (!is_usable) ++ return false; ++ ++ /* Bring the sequence in @ctxt up to date */ ++ ctxt->seq = nbcon_seq_read(con); ++ ++ return prb_read_valid(prb, ctxt->seq, NULL); ++} ++ ++/** ++ * nbcon_kthread_func - The printer thread function ++ * @__console: Console to operate on ++ */ ++static int nbcon_kthread_func(void *__console) ++{ ++ struct console *con = __console; ++ struct nbcon_write_context wctxt = { ++ .ctxt.console = con, ++ .ctxt.prio = NBCON_PRIO_NORMAL, ++ }; ++ struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt); ++ unsigned long flags; ++ short con_flags; ++ bool backlog; ++ int cookie; ++ int ret; ++ ++wait_for_event: ++ /* ++ * Guarantee this task is visible on the rcuwait before ++ * checking the wake condition. ++ * ++ * The full memory barrier within set_current_state() of ++ * ___rcuwait_wait_event() pairs with the full memory ++ * barrier within rcuwait_has_sleeper(). ++ * ++ * This pairs with rcuwait_has_sleeper:A and nbcon_kthread_wake:A. ++ */ ++ ret = rcuwait_wait_event(&con->rcuwait, ++ nbcon_kthread_should_wakeup(con, ctxt), ++ TASK_INTERRUPTIBLE); /* LMM(nbcon_kthread_func:A) */ ++ ++ if (kthread_should_stop()) ++ return 0; ++ ++ /* Wait was interrupted by a spurious signal, go back to sleep. */ ++ if (ret) ++ goto wait_for_event; ++ ++ do { ++ backlog = false; ++ ++ cookie = console_srcu_read_lock(); ++ ++ con_flags = console_srcu_read_flags(con); ++ ++ if (console_is_usable(con, con_flags)) { ++ con->driver_enter(con, &flags); ++ ++ /* ++ * Ensure this stays on the CPU to make handover and ++ * takeover possible. ++ */ ++ cant_migrate(); ++ ++ if (nbcon_context_try_acquire(ctxt)) { ++ /* ++ * If the emit fails, this context is no ++ * longer the owner. ++ */ ++ if (nbcon_emit_next_record(&wctxt, false)) { ++ nbcon_context_release(ctxt); ++ backlog = ctxt->backlog; ++ } ++ } ++ ++ con->driver_exit(con, flags); ++ } ++ ++ console_srcu_read_unlock(cookie); ++ ++ } while (backlog); ++ ++ goto wait_for_event; ++} ++ + /* Track the nbcon emergency nesting per CPU. */ + static DEFINE_PER_CPU(unsigned int, nbcon_pcpu_emergency_nesting); + static unsigned int early_nbcon_pcpu_emergency_nesting __initdata; +@@ -976,7 +1099,7 @@ static bool nbcon_atomic_emit_one(struct + * handed over or taken over. In both cases the context is no + * longer valid. + */ +- if (!nbcon_emit_next_record(wctxt)) ++ if (!nbcon_emit_next_record(wctxt, true)) + return false; + + nbcon_context_release(ctxt); +@@ -1192,6 +1315,63 @@ void nbcon_cpu_emergency_exit(void) + } + + /** ++ * nbcon_kthread_stop - Stop a printer thread ++ * @con: Console to operate on ++ */ ++static void nbcon_kthread_stop(struct console *con) ++{ ++ lockdep_assert_console_list_lock_held(); ++ ++ if (!con->kthread) ++ return; ++ ++ kthread_stop(con->kthread); ++ con->kthread = NULL; ++} ++ ++/** ++ * nbcon_kthread_create - Create a printer thread ++ * @con: Console to operate on ++ * ++ * If it fails, let the console proceed. The atomic part might ++ * be usable and useful. ++ */ ++void nbcon_kthread_create(struct console *con) ++{ ++ struct task_struct *kt; ++ ++ lockdep_assert_console_list_lock_held(); ++ ++ if (!(con->flags & CON_NBCON) || !con->write_thread) ++ return; ++ ++ if (con->kthread) ++ return; ++ ++ /* ++ * Printer threads cannot be started as long as any boot console is ++ * registered because there is no way to synchronize the hardware ++ * registers between boot console code and regular console code. ++ */ ++ if (have_boot_console) ++ return; ++ ++ kt = kthread_run(nbcon_kthread_func, con, "pr/%s%d", con->name, con->index); ++ if (IS_ERR(kt)) { ++ con_printk(KERN_ERR, con, "failed to start printing thread\n"); ++ return; ++ } ++ ++ con->kthread = kt; ++ ++ /* ++ * It is important that console printing threads are scheduled ++ * shortly after a printk call and with generous runtime budgets. ++ */ ++ sched_set_normal(con->kthread, -20); ++} ++ ++/** + * nbcon_alloc - Allocate buffers needed by the nbcon console + * @con: Console to allocate buffers for + * +@@ -1237,6 +1417,7 @@ void nbcon_init(struct console *con) + /* nbcon_alloc() must have been called and successful! */ + BUG_ON(!con->pbufs); + ++ rcuwait_init(&con->rcuwait); + nbcon_seq_force(con, con->seq); + nbcon_state_set(con, &state); + } +@@ -1249,6 +1430,7 @@ void nbcon_free(struct console *con) + { + struct nbcon_state state = { }; + ++ nbcon_kthread_stop(con); + nbcon_state_set(con, &state); + + /* Boot consoles share global printk buffers. */ +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -2689,6 +2689,8 @@ void suspend_console(void) + void resume_console(void) + { + struct console *con; ++ short flags; ++ int cookie; + + if (!console_suspend_enabled) + return; +@@ -2705,6 +2707,14 @@ void resume_console(void) + */ + synchronize_srcu(&console_srcu); + ++ cookie = console_srcu_read_lock(); ++ for_each_console_srcu(con) { ++ flags = console_srcu_read_flags(con); ++ if (flags & CON_NBCON) ++ nbcon_kthread_wake(con); ++ } ++ console_srcu_read_unlock(cookie); ++ + pr_flush(1000, true); + } + +@@ -3025,6 +3035,13 @@ static bool console_flush_all(bool do_co + u64 printk_seq; + bool progress; + ++ /* ++ * console_flush_all() is only for legacy consoles, ++ * unless the nbcon console has no kthread printer. ++ */ ++ if ((flags & CON_NBCON) && con->kthread) ++ continue; ++ + if (!console_is_usable(con, flags)) + continue; + any_usable = true; +@@ -3320,9 +3337,23 @@ EXPORT_SYMBOL(console_stop); + + void console_start(struct console *console) + { ++ short flags; ++ + console_list_lock(); + console_srcu_write_flags(console, console->flags | CON_ENABLED); ++ flags = console->flags; + console_list_unlock(); ++ ++ /* ++ * Ensure that all SRCU list walks have completed. The related ++ * printing context must be able to see it is enabled so that ++ * it is guaranteed to wake up and resume printing. ++ */ ++ synchronize_srcu(&console_srcu); ++ ++ if (flags & CON_NBCON) ++ nbcon_kthread_wake(console); ++ + __pr_flush(console, 1000, true); + } + EXPORT_SYMBOL(console_start); |