diff options
Diffstat (limited to 'debian/patches-rt/0044-printk-Add-kthread-for-all-legacy-consoles.patch')
| -rw-r--r-- | debian/patches-rt/0044-printk-Add-kthread-for-all-legacy-consoles.patch | 532 |
1 files changed, 532 insertions, 0 deletions
diff --git a/debian/patches-rt/0044-printk-Add-kthread-for-all-legacy-consoles.patch b/debian/patches-rt/0044-printk-Add-kthread-for-all-legacy-consoles.patch new file mode 100644 index 000000000..edcfbb989 --- /dev/null +++ b/debian/patches-rt/0044-printk-Add-kthread-for-all-legacy-consoles.patch @@ -0,0 +1,532 @@ +From: John Ogness <john.ogness@linutronix.de> +Date: Fri, 22 Sep 2023 17:35:04 +0000 +Subject: [PATCH 44/46] printk: Add kthread for all legacy consoles +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.9/older/patches-6.9-rt5.tar.xz + +The write callback of legacy consoles makes use of spinlocks. +This is not permitted with PREEMPT_RT in atomic contexts. + +For PREEMPT_RT, create a new kthread to handle printing of all +the legacy consoles (and nbcon consoles if boot consoles are +registered). + +Since, if running from the kthread, the consoles are printing +in a task context, the legacy nbcon printing can use the +device_lock(), write_thread(), device_unlock() callbacks for +printing. + +Introduce the macro force_printkthreads() to query if the +forced threading of legacy consoles is in effect. + +These changes only affect 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 | 11 +- + kernel/printk/nbcon.c | 52 ++++++---- + kernel/printk/printk.c | 242 ++++++++++++++++++++++++++++++++++++++--------- + 3 files changed, 243 insertions(+), 62 deletions(-) + +--- a/kernel/printk/internal.h ++++ b/kernel/printk/internal.h +@@ -21,6 +21,12 @@ int devkmsg_sysctl_set_loglvl(struct ctl + (con->flags & CON_BOOT) ? "boot" : "", \ + con->name, con->index, ##__VA_ARGS__) + ++#ifdef CONFIG_PREEMPT_RT ++# define force_printkthreads() (true) ++#else ++# define force_printkthreads() (false) ++#endif ++ + #ifdef CONFIG_PRINTK + + #ifdef CONFIG_PRINTK_CALLER +@@ -90,9 +96,10 @@ void nbcon_free(struct console *con); + enum nbcon_prio nbcon_get_default_prio(void); + void nbcon_atomic_flush_pending(void); + bool nbcon_legacy_emit_next_record(struct console *con, bool *handover, +- int cookie); ++ int cookie, bool use_atomic); + 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 +@@ -179,7 +186,7 @@ static inline void nbcon_free(struct 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 nbcon_legacy_emit_next_record(struct console *con, bool *handover, +- int cookie) { return false; } ++ int cookie, bool use_atomic) { return false; } + + static inline bool console_is_usable(struct console *con, short flags, + bool use_atomic) { return false; } +--- a/kernel/printk/nbcon.c ++++ b/kernel/printk/nbcon.c +@@ -1224,9 +1224,10 @@ enum nbcon_prio nbcon_get_default_prio(v + } + + /* +- * nbcon_atomic_emit_one - Print one record for an nbcon console using the +- * write_atomic() callback ++ * nbcon_emit_one - Print one record for an nbcon console using the ++ * specified callback + * @wctxt: An initialized write context struct to use for this context ++ * @use_atomic: True if the write_atomic callback is to be used + * + * Return: True, when a record has been printed and there are still + * pending records. The caller might want to continue flushing. +@@ -1239,7 +1240,7 @@ enum nbcon_prio nbcon_get_default_prio(v + * This is an internal helper to handle the locking of the console before + * calling nbcon_emit_next_record(). + */ +-static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt) ++static bool nbcon_emit_one(struct nbcon_write_context *wctxt, bool use_atomic) + { + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + +@@ -1254,7 +1255,7 @@ static bool nbcon_atomic_emit_one(struct + * The higher priority printing context takes over responsibility + * to print the pending records. + */ +- if (!nbcon_emit_next_record(wctxt, true)) ++ if (!nbcon_emit_next_record(wctxt, use_atomic)) + return false; + + nbcon_context_release(ctxt); +@@ -1271,6 +1272,7 @@ static bool nbcon_atomic_emit_one(struct + * both the console_lock and the SRCU read lock. Otherwise it + * is set to false. + * @cookie: The cookie from the SRCU read lock. ++ * @use_atomic: True if the write_atomic callback is to be used + * + * Context: Any context except NMI. + * Return: True, when a record has been printed and there are still +@@ -1286,26 +1288,38 @@ static bool nbcon_atomic_emit_one(struct + * Essentially it is the nbcon version of console_emit_next_record(). + */ + bool nbcon_legacy_emit_next_record(struct console *con, bool *handover, +- int cookie) ++ int cookie, bool use_atomic) + { + struct nbcon_write_context wctxt = { }; + struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt); + unsigned long flags; + bool progress; + +- /* Use the same procedure as console_emit_next_record(). */ +- printk_safe_enter_irqsave(flags); +- console_lock_spinning_enable(); +- stop_critical_timings(); +- +- ctxt->console = con; +- ctxt->prio = nbcon_get_default_prio(); +- +- progress = nbcon_atomic_emit_one(&wctxt); +- +- start_critical_timings(); +- *handover = console_lock_spinning_disable_and_check(cookie); +- printk_safe_exit_irqrestore(flags); ++ ctxt->console = con; ++ ++ if (use_atomic) { ++ /* Use the same procedure as console_emit_next_record(). */ ++ printk_safe_enter_irqsave(flags); ++ console_lock_spinning_enable(); ++ stop_critical_timings(); ++ ++ ctxt->prio = nbcon_get_default_prio(); ++ progress = nbcon_emit_one(&wctxt, use_atomic); ++ ++ start_critical_timings(); ++ *handover = console_lock_spinning_disable_and_check(cookie); ++ printk_safe_exit_irqrestore(flags); ++ } else { ++ *handover = false; ++ ++ con->device_lock(con, &flags); ++ cant_migrate(); ++ ++ ctxt->prio = nbcon_get_default_prio(); ++ progress = nbcon_emit_one(&wctxt, use_atomic); ++ ++ con->device_unlock(con, flags); ++ } + + return progress; + } +@@ -1622,6 +1636,8 @@ static int __init printk_setup_threads(v + printk_threads_enabled = true; + for_each_console(con) + nbcon_kthread_create(con); ++ if (force_printkthreads() && 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 && ++ !force_printkthreads(); + int printed_len; + + /* Suppress unimportant messages after panic happens */ +@@ -2468,6 +2472,14 @@ 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 +@@ -2481,6 +2493,8 @@ 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 +@@ -2726,6 +2740,8 @@ void resume_console(void) + } + console_srcu_read_unlock(cookie); + ++ wake_up_legacy_kthread(); ++ + pr_flush(1000, true); + } + +@@ -2740,7 +2756,8 @@ 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 && ++ !force_printkthreads()) { + /* If trylock fails, someone else is doing the printing */ + if (console_trylock()) + console_unlock(); +@@ -3000,31 +3017,43 @@ 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 (force_printkthreads()) { ++ /* ++ * With forced threading 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; + } +@@ -3088,12 +3117,13 @@ static bool console_flush_all(bool do_co + if ((flags & CON_NBCON) && con->kthread) + continue; + +- if (!console_is_usable(con, flags, true)) ++ if (!console_is_usable(con, flags, !do_cond_resched)) + continue; + any_usable = true; + + if (flags & CON_NBCON) { +- progress = nbcon_legacy_emit_next_record(con, handover, cookie); ++ progress = nbcon_legacy_emit_next_record(con, handover, cookie, ++ !do_cond_resched); + printk_seq = nbcon_seq_read(con); + } else { + progress = console_emit_next_record(con, handover, cookie); +@@ -3132,19 +3162,7 @@ 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; +@@ -3188,6 +3206,32 @@ 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) ++{ ++ /* ++ * Forced threading relies on kthread and atomic consoles for ++ * printing. It never attempts to print from console_unlock(). ++ */ ++ if (force_printkthreads()) { ++ __console_unlock(); ++ return; ++ } ++ ++ console_flush_and_unlock(); ++} + EXPORT_SYMBOL(console_unlock); + + /** +@@ -3397,11 +3441,106 @@ 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 (!force_printkthreads()) ++ 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) +@@ -3690,6 +3829,7 @@ void register_console(struct console *ne + } else { + have_legacy_console = true; + newcon->seq = init_seq; ++ nbcon_legacy_kthread_create(); + } + + if (newcon->flags & CON_BOOT) +@@ -3856,6 +3996,13 @@ 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; + } + +@@ -4014,8 +4161,12 @@ 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 && !force_printkthreads()) { + console_lock(); + console_unlock(); + } +@@ -4129,9 +4280,16 @@ 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 (force_printkthreads()) { ++ wake_up_legacy_kthread(); ++ } else { ++ /* ++ * If trylock fails, some other context ++ * will do the printing. ++ */ ++ if (console_trylock()) ++ console_unlock(); ++ } + } + + if (pending & PRINTK_PENDING_WAKEUP) |