diff options
Diffstat (limited to '')
| -rw-r--r-- | debian/patches-rt/0132-printk-Add-kthread-for-all-legacy-consoles.patch | 422 |
1 files changed, 422 insertions, 0 deletions
diff --git a/debian/patches-rt/0132-printk-Add-kthread-for-all-legacy-consoles.patch b/debian/patches-rt/0132-printk-Add-kthread-for-all-legacy-consoles.patch new file mode 100644 index 000000000..7c46be713 --- /dev/null +++ b/debian/patches-rt/0132-printk-Add-kthread-for-all-legacy-consoles.patch @@ -0,0 +1,422 @@ +From: John Ogness <john.ogness@linutronix.de> +Date: Fri, 22 Sep 2023 17:35:04 +0000 +Subject: [PATCH 132/134] printk: Add kthread for all legacy consoles +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz + +The write callback of legacy consoles make use of spinlocks. +This is not permitted with PREEMPT_RT in atomic contexts. + +Create a new kthread to handle printing of all the legacy +consoles (and nbcon consoles if boot consoles are registered). + +Since the consoles are printing in a task context, it is no +longer appropriate to support the legacy handover mechanism. + +These changes exist only for CONFIG_PREEMPT_RT. + +Signed-off-by: John Ogness <john.ogness@linutronix.de> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/printk/internal.h | 1 + kernel/printk/nbcon.c | 18 ++- + kernel/printk/printk.c | 237 +++++++++++++++++++++++++++++++++++++++-------- + 3 files changed, 210 insertions(+), 46 deletions(-) + +--- a/kernel/printk/internal.h ++++ b/kernel/printk/internal.h +@@ -95,6 +95,7 @@ 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); + void nbcon_wake_threads(void); ++void nbcon_legacy_kthread_create(void); + + /* + * Check if the given console is currently capable and allowed to print +--- a/kernel/printk/nbcon.c ++++ b/kernel/printk/nbcon.c +@@ -1247,9 +1247,11 @@ bool nbcon_atomic_emit_next_record(struc + *handover = false; + + /* Use the same locking order as console_emit_next_record(). */ +- printk_safe_enter_irqsave(flags); +- console_lock_spinning_enable(); +- stop_critical_timings(); ++ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { ++ printk_safe_enter_irqsave(flags); ++ console_lock_spinning_enable(); ++ stop_critical_timings(); ++ } + + con->driver_enter(con, &driver_flags); + cant_migrate(); +@@ -1261,9 +1263,11 @@ bool nbcon_atomic_emit_next_record(struc + + con->driver_exit(con, driver_flags); + +- start_critical_timings(); +- *handover = console_lock_spinning_disable_and_check(cookie); +- printk_safe_exit_irqrestore(flags); ++ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { ++ start_critical_timings(); ++ *handover = console_lock_spinning_disable_and_check(cookie); ++ printk_safe_exit_irqrestore(flags); ++ } + + return progress; + } +@@ -1469,6 +1473,8 @@ static int __init printk_setup_threads(v + printk_threads_enabled = true; + for_each_console(con) + nbcon_kthread_create(con); ++ if (IS_ENABLED(CONFIG_PREEMPT_RT) && printing_via_unlock) ++ nbcon_legacy_kthread_create(); + console_list_unlock(); + return 0; + } +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -487,6 +487,9 @@ bool have_boot_console; + + #ifdef CONFIG_PRINTK + DECLARE_WAIT_QUEUE_HEAD(log_wait); ++ ++static DECLARE_WAIT_QUEUE_HEAD(legacy_wait); ++ + /* All 3 protected by @syslog_lock. */ + /* the next printk record to read by syslog(READ) or /proc/kmsg */ + static u64 syslog_seq; +@@ -2345,7 +2348,8 @@ asmlinkage int vprintk_emit(int facility + const struct dev_printk_info *dev_info, + const char *fmt, va_list args) + { +- bool do_trylock_unlock = printing_via_unlock; ++ bool do_trylock_unlock = printing_via_unlock && ++ !IS_ENABLED(CONFIG_PREEMPT_RT); + int printed_len; + + /* Suppress unimportant messages after panic happens */ +@@ -2473,6 +2477,14 @@ EXPORT_SYMBOL(_printk); + static bool pr_flush(int timeout_ms, bool reset_on_progress); + static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress); + ++static struct task_struct *nbcon_legacy_kthread; ++ ++static inline void wake_up_legacy_kthread(void) ++{ ++ if (nbcon_legacy_kthread) ++ wake_up_interruptible(&legacy_wait); ++} ++ + #else /* CONFIG_PRINTK */ + + #define printk_time false +@@ -2486,6 +2498,8 @@ static u64 syslog_seq; + static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; } + static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; } + ++static inline void nbcon_legacy_kthread_create(void) { } ++static inline void wake_up_legacy_kthread(void) { } + #endif /* CONFIG_PRINTK */ + + #ifdef CONFIG_EARLY_PRINTK +@@ -2723,6 +2737,8 @@ void resume_console(void) + } + console_srcu_read_unlock(cookie); + ++ wake_up_legacy_kthread(); ++ + pr_flush(1000, true); + } + +@@ -2737,7 +2753,8 @@ void resume_console(void) + */ + static int console_cpu_notify(unsigned int cpu) + { +- if (!cpuhp_tasks_frozen && printing_via_unlock) { ++ if (!cpuhp_tasks_frozen && printing_via_unlock && ++ !IS_ENABLED(CONFIG_PREEMPT_RT)) { + /* If trylock fails, someone else is doing the printing */ + if (console_trylock()) + console_unlock(); +@@ -2962,31 +2979,43 @@ static bool console_emit_next_record(str + con->dropped = 0; + } + +- /* +- * While actively printing out messages, if another printk() +- * were to occur on another CPU, it may wait for this one to +- * finish. This task can not be preempted if there is a +- * waiter waiting to take over. +- * +- * Interrupts are disabled because the hand over to a waiter +- * must not be interrupted until the hand over is completed +- * (@console_waiter is cleared). +- */ +- printk_safe_enter_irqsave(flags); +- console_lock_spinning_enable(); ++ /* Write everything out to the hardware. */ + +- /* Do not trace print latency. */ +- stop_critical_timings(); ++ if (IS_ENABLED(CONFIG_PREEMPT_RT)) { ++ /* ++ * On PREEMPT_RT this function is either in a thread or ++ * panic context. So there is no need for concern about ++ * printk reentrance or handovers. ++ */ + +- /* Write everything out to the hardware. */ +- con->write(con, outbuf, pmsg.outbuf_len); ++ con->write(con, outbuf, pmsg.outbuf_len); ++ con->seq = pmsg.seq + 1; ++ } else { ++ /* ++ * While actively printing out messages, if another printk() ++ * were to occur on another CPU, it may wait for this one to ++ * finish. This task can not be preempted if there is a ++ * waiter waiting to take over. ++ * ++ * Interrupts are disabled because the hand over to a waiter ++ * must not be interrupted until the hand over is completed ++ * (@console_waiter is cleared). ++ */ ++ printk_safe_enter_irqsave(flags); ++ console_lock_spinning_enable(); + +- start_critical_timings(); ++ /* Do not trace print latency. */ ++ stop_critical_timings(); + +- con->seq = pmsg.seq + 1; ++ con->write(con, outbuf, pmsg.outbuf_len); + +- *handover = console_lock_spinning_disable_and_check(cookie); +- printk_safe_exit_irqrestore(flags); ++ start_critical_timings(); ++ ++ con->seq = pmsg.seq + 1; ++ ++ *handover = console_lock_spinning_disable_and_check(cookie); ++ printk_safe_exit_irqrestore(flags); ++ } + skip: + return true; + } +@@ -3096,19 +3125,7 @@ static bool console_flush_all(bool do_co + return false; + } + +-/** +- * console_unlock - unblock the console subsystem from printing +- * +- * Releases the console_lock which the caller holds to block printing of +- * the console subsystem. +- * +- * While the console_lock was held, console output may have been buffered +- * by printk(). If this is the case, console_unlock(); emits +- * the output prior to releasing the lock. +- * +- * console_unlock(); may be called from any context. +- */ +-void console_unlock(void) ++static void console_flush_and_unlock(void) + { + bool do_cond_resched; + bool handover; +@@ -3152,6 +3169,32 @@ void console_unlock(void) + */ + } while (prb_read_valid(prb, next_seq, NULL) && console_trylock()); + } ++ ++/** ++ * console_unlock - unblock the console subsystem from printing ++ * ++ * Releases the console_lock which the caller holds to block printing of ++ * the console subsystem. ++ * ++ * While the console_lock was held, console output may have been buffered ++ * by printk(). If this is the case, console_unlock(); emits ++ * the output prior to releasing the lock. ++ * ++ * console_unlock(); may be called from any context. ++ */ ++void console_unlock(void) ++{ ++ /* ++ * PREEMPT_RT relies on kthread and atomic consoles for printing. ++ * It never attempts to print from console_unlock(). ++ */ ++ if (IS_ENABLED(CONFIG_PREEMPT_RT)) { ++ __console_unlock(); ++ return; ++ } ++ ++ console_flush_and_unlock(); ++} + EXPORT_SYMBOL(console_unlock); + + /** +@@ -3361,11 +3404,106 @@ void console_start(struct console *conso + + if (flags & CON_NBCON) + nbcon_kthread_wake(console); ++ else ++ wake_up_legacy_kthread(); + + __pr_flush(console, 1000, true); + } + EXPORT_SYMBOL(console_start); + ++#ifdef CONFIG_PRINTK ++static bool printer_should_wake(void) ++{ ++ bool available = false; ++ struct console *con; ++ int cookie; ++ ++ if (kthread_should_stop()) ++ return true; ++ ++ cookie = console_srcu_read_lock(); ++ for_each_console_srcu(con) { ++ short flags = console_srcu_read_flags(con); ++ u64 printk_seq; ++ ++ /* ++ * The legacy printer thread 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, true)) ++ continue; ++ ++ if (flags & CON_NBCON) { ++ printk_seq = nbcon_seq_read(con); ++ } else { ++ /* ++ * It is safe to read @seq because only this ++ * thread context updates @seq. ++ */ ++ printk_seq = con->seq; ++ } ++ ++ if (prb_read_valid(prb, printk_seq, NULL)) { ++ available = true; ++ break; ++ } ++ } ++ console_srcu_read_unlock(cookie); ++ ++ return available; ++} ++ ++static int nbcon_legacy_kthread_func(void *unused) ++{ ++ int error; ++ ++ for (;;) { ++ error = wait_event_interruptible(legacy_wait, printer_should_wake()); ++ ++ if (kthread_should_stop()) ++ break; ++ ++ if (error) ++ continue; ++ ++ console_lock(); ++ console_flush_and_unlock(); ++ } ++ ++ return 0; ++} ++ ++void nbcon_legacy_kthread_create(void) ++{ ++ struct task_struct *kt; ++ ++ lockdep_assert_held(&console_mutex); ++ ++ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) ++ return; ++ ++ if (!printk_threads_enabled || nbcon_legacy_kthread) ++ return; ++ ++ kt = kthread_run(nbcon_legacy_kthread_func, NULL, "pr/legacy"); ++ if (IS_ERR(kt)) { ++ pr_err("unable to start legacy printing thread\n"); ++ return; ++ } ++ ++ nbcon_legacy_kthread = kt; ++ ++ /* ++ * It is important that console printing threads are scheduled ++ * shortly after a printk call and with generous runtime budgets. ++ */ ++ sched_set_normal(nbcon_legacy_kthread, -20); ++} ++#endif /* CONFIG_PRINTK */ ++ + static int __read_mostly keep_bootcon; + + static int __init keep_bootcon_setup(char *str) +@@ -3632,6 +3770,7 @@ void register_console(struct console *ne + nbcon_init(newcon); + } else { + have_legacy_console = true; ++ nbcon_legacy_kthread_create(); + } + + if (newcon->flags & CON_BOOT) +@@ -3770,6 +3909,13 @@ static int unregister_console_locked(str + nbcon_kthread_create(c); + } + ++#ifdef CONFIG_PRINTK ++ if (!printing_via_unlock && nbcon_legacy_kthread) { ++ kthread_stop(nbcon_legacy_kthread); ++ nbcon_legacy_kthread = NULL; ++ } ++#endif ++ + return res; + } + +@@ -3929,8 +4075,12 @@ static bool __pr_flush(struct console *c + + seq = prb_next_reserve_seq(prb); + +- /* Flush the consoles so that records up to @seq are printed. */ +- if (printing_via_unlock) { ++ /* ++ * Flush the consoles so that records up to @seq are printed. ++ * Otherwise this function will just wait for the threaded printers ++ * to print up to @seq. ++ */ ++ if (printing_via_unlock && !IS_ENABLED(CONFIG_PREEMPT_RT)) { + console_lock(); + console_unlock(); + } +@@ -4038,9 +4188,16 @@ static void wake_up_klogd_work_func(stru + int pending = this_cpu_xchg(printk_pending, 0); + + if (pending & PRINTK_PENDING_OUTPUT) { +- /* If trylock fails, someone else is doing the printing */ +- if (console_trylock()) +- console_unlock(); ++ if (IS_ENABLED(CONFIG_PREEMPT_RT)) { ++ wake_up_interruptible(&legacy_wait); ++ } else { ++ /* ++ * If trylock fails, some other context ++ * will do the printing. ++ */ ++ if (console_trylock()) ++ console_unlock(); ++ } + } + + if (pending & PRINTK_PENDING_WAKEUP) |