diff options
Diffstat (limited to 'debian/patches-rt/0019-printk-Bring-back-the-RT-bits.patch')
| -rw-r--r-- | debian/patches-rt/0019-printk-Bring-back-the-RT-bits.patch | 1234 |
1 files changed, 1234 insertions, 0 deletions
diff --git a/debian/patches-rt/0019-printk-Bring-back-the-RT-bits.patch b/debian/patches-rt/0019-printk-Bring-back-the-RT-bits.patch new file mode 100644 index 000000000..969f44377 --- /dev/null +++ b/debian/patches-rt/0019-printk-Bring-back-the-RT-bits.patch @@ -0,0 +1,1234 @@ +From dd4e52ae061806da556008ca819481befcff0fd3 Mon Sep 17 00:00:00 2001 +From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Date: Tue, 19 Jul 2022 20:08:01 +0200 +Subject: [PATCH 19/62] printk: Bring back the RT bits. +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.1/older/patches-6.1.69-rt21.tar.xz + +This is a revert of the commits: +| 07a22b61946f0 Revert "printk: add functions to prefer direct printing" +| 5831788afb17b Revert "printk: add kthread console printers" +| 2d9ef940f89e0 Revert "printk: extend console_lock for per-console locking" +| 007eeab7e9f03 Revert "printk: remove @console_locked" +| 05c96b3713aa2 Revert "printk: Block console kthreads when direct printing will be required" +| 20fb0c8272bbb Revert "printk: Wait for the global console lock when the system is going down" + +which is needed for the atomic consoles which are used on PREEMPT_RT. + +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + drivers/tty/sysrq.c | 2 + + include/linux/console.h | 17 ++ + include/linux/printk.h | 15 + + kernel/hung_task.c | 11 +- + kernel/panic.c | 4 + + kernel/printk/internal.h | 2 + + kernel/printk/printk.c | 586 ++++++++++++++++++++++++++++++++---- + kernel/printk/printk_safe.c | 32 ++ + kernel/rcu/tree_stall.h | 2 + + kernel/reboot.c | 16 +- + kernel/watchdog.c | 4 + + kernel/watchdog_hld.c | 4 + + 12 files changed, 636 insertions(+), 59 deletions(-) + +diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c +index 248067197287..0db9dad8c99f 100644 +--- a/drivers/tty/sysrq.c ++++ b/drivers/tty/sysrq.c +@@ -582,6 +582,7 @@ void __handle_sysrq(int key, bool check_mask) + + rcu_sysrq_start(); + rcu_read_lock(); ++ printk_prefer_direct_enter(); + /* + * Raise the apparent loglevel to maximum so that the sysrq header + * is shown to provide the user with positive feedback. We do not +@@ -623,6 +624,7 @@ void __handle_sysrq(int key, bool check_mask) + pr_cont("\n"); + console_loglevel = orig_log_level; + } ++ printk_prefer_direct_exit(); + rcu_read_unlock(); + rcu_sysrq_end(); + +diff --git a/include/linux/console.h b/include/linux/console.h +index 8c1686e2c233..143653090c48 100644 +--- a/include/linux/console.h ++++ b/include/linux/console.h +@@ -16,6 +16,7 @@ + + #include <linux/atomic.h> + #include <linux/types.h> ++#include <linux/mutex.h> + + struct vc_data; + struct console_font_op; +@@ -153,6 +154,22 @@ struct console { + uint ospeed; + u64 seq; + unsigned long dropped; ++ struct task_struct *thread; ++ bool blocked; ++ ++ /* ++ * The per-console lock is used by printing kthreads to synchronize ++ * this console with callers of console_lock(). This is necessary in ++ * order to allow printing kthreads to run in parallel to each other, ++ * while each safely accessing the @blocked field and synchronizing ++ * against direct printing via console_lock/console_unlock. ++ * ++ * Note: For synchronizing against direct printing via ++ * console_trylock/console_unlock, see the static global ++ * variable @console_kthreads_active. ++ */ ++ struct mutex lock; ++ + void *data; + struct console *next; + }; +diff --git a/include/linux/printk.h b/include/linux/printk.h +index 8c81806c2e99..f8c4e4fa6d7d 100644 +--- a/include/linux/printk.h ++++ b/include/linux/printk.h +@@ -168,6 +168,9 @@ extern void __printk_safe_exit(void); + */ + #define printk_deferred_enter __printk_safe_enter + #define printk_deferred_exit __printk_safe_exit ++extern void printk_prefer_direct_enter(void); ++extern void printk_prefer_direct_exit(void); ++extern void try_block_console_kthreads(int timeout_ms); + + /* + * Please don't use printk_ratelimit(), because it shares ratelimiting state +@@ -219,6 +222,18 @@ static inline void printk_deferred_exit(void) + { + } + ++static inline void printk_prefer_direct_enter(void) ++{ ++} ++ ++static inline void printk_prefer_direct_exit(void) ++{ ++} ++ ++static inline void try_block_console_kthreads(int timeout_ms) ++{ ++} ++ + static inline int printk_ratelimit(void) + { + return 0; +diff --git a/kernel/hung_task.c b/kernel/hung_task.c +index c71889f3f3fc..e2d2344cb9f4 100644 +--- a/kernel/hung_task.c ++++ b/kernel/hung_task.c +@@ -127,6 +127,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout) + * complain: + */ + if (sysctl_hung_task_warnings) { ++ printk_prefer_direct_enter(); ++ + if (sysctl_hung_task_warnings > 0) + sysctl_hung_task_warnings--; + pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", +@@ -142,6 +144,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout) + + if (sysctl_hung_task_all_cpu_backtrace) + hung_task_show_all_bt = true; ++ ++ printk_prefer_direct_exit(); + } + + touch_nmi_watchdog(); +@@ -212,12 +216,17 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout) + } + unlock: + rcu_read_unlock(); +- if (hung_task_show_lock) ++ if (hung_task_show_lock) { ++ printk_prefer_direct_enter(); + debug_show_all_locks(); ++ printk_prefer_direct_exit(); ++ } + + if (hung_task_show_all_bt) { + hung_task_show_all_bt = false; ++ printk_prefer_direct_enter(); + trigger_all_cpu_backtrace(); ++ printk_prefer_direct_exit(); + } + + if (hung_task_call_panic) +diff --git a/kernel/panic.c b/kernel/panic.c +index 63e94f3bd8dc..88cd873c7c30 100644 +--- a/kernel/panic.c ++++ b/kernel/panic.c +@@ -653,6 +653,8 @@ void __warn(const char *file, int line, void *caller, unsigned taint, + { + disable_trace_on_warning(); + ++ printk_prefer_direct_enter(); ++ + if (file) + pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS\n", + raw_smp_processor_id(), current->pid, file, line, +@@ -681,6 +683,8 @@ void __warn(const char *file, int line, void *caller, unsigned taint, + + /* Just a warning, don't kill lockdep. */ + add_taint(taint, LOCKDEP_STILL_OK); ++ ++ printk_prefer_direct_exit(); + } + + #ifndef __WARN_FLAGS +diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h +index d947ca6c84f9..e7d8578860ad 100644 +--- a/kernel/printk/internal.h ++++ b/kernel/printk/internal.h +@@ -20,6 +20,8 @@ enum printk_info_flags { + LOG_CONT = 8, /* text is a fragment of a continuation line */ + }; + ++extern bool block_console_kthreads; ++ + __printf(4, 0) + int vprintk_store(int facility, int level, + const struct dev_printk_info *dev_info, +diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c +index cc53fb77f77c..e9f9b66608a0 100644 +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -220,6 +220,36 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write, + } + #endif /* CONFIG_PRINTK && CONFIG_SYSCTL */ + ++/* ++ * Used to synchronize printing kthreads against direct printing via ++ * console_trylock/console_unlock. ++ * ++ * Values: ++ * -1 = console kthreads atomically blocked (via global trylock) ++ * 0 = no kthread printing, console not locked (via trylock) ++ * >0 = kthread(s) actively printing ++ * ++ * Note: For synchronizing against direct printing via ++ * console_lock/console_unlock, see the @lock variable in ++ * struct console. ++ */ ++static atomic_t console_kthreads_active = ATOMIC_INIT(0); ++ ++#define console_kthreads_atomic_tryblock() \ ++ (atomic_cmpxchg(&console_kthreads_active, 0, -1) == 0) ++#define console_kthreads_atomic_unblock() \ ++ atomic_cmpxchg(&console_kthreads_active, -1, 0) ++#define console_kthreads_atomically_blocked() \ ++ (atomic_read(&console_kthreads_active) == -1) ++ ++#define console_kthread_printing_tryenter() \ ++ atomic_inc_unless_negative(&console_kthreads_active) ++#define console_kthread_printing_exit() \ ++ atomic_dec(&console_kthreads_active) ++ ++/* Block console kthreads to avoid processing new messages. */ ++bool block_console_kthreads; ++ + /* + * Helper macros to handle lockdep when locking/unlocking console_sem. We use + * macros instead of functions so that _RET_IP_ contains useful information. +@@ -268,14 +298,49 @@ static bool panic_in_progress(void) + } + + /* +- * This is used for debugging the mess that is the VT code by +- * keeping track if we have the console semaphore held. It's +- * definitely not the perfect debug tool (we don't know if _WE_ +- * hold it and are racing, but it helps tracking those weird code +- * paths in the console code where we end up in places I want +- * locked without the console semaphore held). ++ * Tracks whether kthread printers are all blocked. A value of true implies ++ * that the console is locked via console_lock() or the console is suspended. ++ * Writing to this variable requires holding @console_sem. ++ */ ++static bool console_kthreads_blocked; ++ ++/* ++ * Block all kthread printers from a schedulable context. ++ * ++ * Requires holding @console_sem. ++ */ ++static void console_kthreads_block(void) ++{ ++ struct console *con; ++ ++ for_each_console(con) { ++ mutex_lock(&con->lock); ++ con->blocked = true; ++ mutex_unlock(&con->lock); ++ } ++ ++ console_kthreads_blocked = true; ++} ++ ++/* ++ * Unblock all kthread printers from a schedulable context. ++ * ++ * Requires holding @console_sem. + */ +-static int console_locked, console_suspended; ++static void console_kthreads_unblock(void) ++{ ++ struct console *con; ++ ++ for_each_console(con) { ++ mutex_lock(&con->lock); ++ con->blocked = false; ++ mutex_unlock(&con->lock); ++ } ++ ++ console_kthreads_blocked = false; ++} ++ ++static int console_suspended; + + /* + * Array of consoles built from command line options (console=) +@@ -358,7 +423,75 @@ static int console_msg_format = MSG_FORMAT_DEFAULT; + /* syslog_lock protects syslog_* variables and write access to clear_seq. */ + static DEFINE_MUTEX(syslog_lock); + ++/* ++ * A flag to signify if printk_activate_kthreads() has already started the ++ * kthread printers. If true, any later registered consoles must start their ++ * own kthread directly. The flag is write protected by the console_lock. ++ */ ++static bool printk_kthreads_available; ++ + #ifdef CONFIG_PRINTK ++static atomic_t printk_prefer_direct = ATOMIC_INIT(0); ++ ++/** ++ * printk_prefer_direct_enter - cause printk() calls to attempt direct ++ * printing to all enabled consoles ++ * ++ * Since it is not possible to call into the console printing code from any ++ * context, there is no guarantee that direct printing will occur. ++ * ++ * This globally effects all printk() callers. ++ * ++ * Context: Any context. ++ */ ++void printk_prefer_direct_enter(void) ++{ ++ atomic_inc(&printk_prefer_direct); ++} ++ ++/** ++ * printk_prefer_direct_exit - restore printk() behavior ++ * ++ * Context: Any context. ++ */ ++void printk_prefer_direct_exit(void) ++{ ++ WARN_ON(atomic_dec_if_positive(&printk_prefer_direct) < 0); ++} ++ ++/* ++ * Calling printk() always wakes kthread printers so that they can ++ * flush the new message to their respective consoles. Also, if direct ++ * printing is allowed, printk() tries to flush the messages directly. ++ * ++ * Direct printing is allowed in situations when the kthreads ++ * are not available or the system is in a problematic state. ++ * ++ * See the implementation about possible races. ++ */ ++static inline bool allow_direct_printing(void) ++{ ++ /* ++ * Checking kthread availability is a possible race because the ++ * kthread printers can become permanently disabled during runtime. ++ * However, doing that requires holding the console_lock, so any ++ * pending messages will be direct printed by console_unlock(). ++ */ ++ if (!printk_kthreads_available) ++ return true; ++ ++ /* ++ * Prefer direct printing when the system is in a problematic state. ++ * The context that sets this state will always see the updated value. ++ * The other contexts do not care. Anyway, direct printing is just a ++ * best effort. The direct output is only possible when console_lock ++ * is not already taken and no kthread printers are actively printing. ++ */ ++ return (system_state > SYSTEM_RUNNING || ++ oops_in_progress || ++ atomic_read(&printk_prefer_direct)); ++} ++ + DECLARE_WAIT_QUEUE_HEAD(log_wait); + /* All 3 protected by @syslog_lock. */ + /* the next printk record to read by syslog(READ) or /proc/kmsg */ +@@ -2249,10 +2382,10 @@ asmlinkage int vprintk_emit(int facility, int level, + printed_len = vprintk_store(facility, level, dev_info, fmt, args); + + /* If called from the scheduler, we can not call up(). */ +- if (!in_sched) { ++ if (!in_sched && allow_direct_printing()) { + /* + * The caller may be holding system-critical or +- * timing-sensitive locks. Disable preemption during ++ * timing-sensitive locks. Disable preemption during direct + * printing of all remaining records to all consoles so that + * this context can return as soon as possible. Hopefully + * another printk() caller will take over the printing. +@@ -2300,6 +2433,8 @@ 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 void printk_start_kthread(struct console *con); ++ + #else /* CONFIG_PRINTK */ + + #define CONSOLE_LOG_MAX 0 +@@ -2334,6 +2469,8 @@ static void call_console_driver(struct console *con, const char *text, size_t le + static bool suppress_message_printing(int level) { return false; } + 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 void printk_start_kthread(struct console *con) { } ++static bool allow_direct_printing(void) { return true; } + + #endif /* CONFIG_PRINTK */ + +@@ -2552,6 +2689,14 @@ static int console_cpu_notify(unsigned int cpu) + /* If trylock fails, someone else is doing the printing */ + if (console_trylock()) + console_unlock(); ++ else { ++ /* ++ * If a new CPU comes online, the conditions for ++ * printer_should_wake() may have changed for some ++ * kthread printer with !CON_ANYTIME. ++ */ ++ wake_up_klogd(); ++ } + } + return 0; + } +@@ -2594,7 +2739,7 @@ void console_lock(void) + down_console_sem(); + if (console_suspended) + return; +- console_locked = 1; ++ console_kthreads_block(); + console_may_schedule = 1; + } + EXPORT_SYMBOL(console_lock); +@@ -2618,15 +2763,30 @@ int console_trylock(void) + up_console_sem(); + return 0; + } +- console_locked = 1; ++ if (!console_kthreads_atomic_tryblock()) { ++ up_console_sem(); ++ return 0; ++ } + console_may_schedule = 0; + return 1; + } + EXPORT_SYMBOL(console_trylock); + ++/* ++ * This is used to help to make sure that certain paths within the VT code are ++ * running with the console lock held. It is definitely not the perfect debug ++ * tool (it is not known if the VT code is the task holding the console lock), ++ * but it helps tracking those weird code paths in the console code such as ++ * when the console is suspended: where the console is not locked but no ++ * console printing may occur. ++ * ++ * Note: This returns true when the console is suspended but is not locked. ++ * This is intentional because the VT code must consider that situation ++ * the same as if the console was locked. ++ */ + int is_console_locked(void) + { +- return console_locked; ++ return (console_kthreads_blocked || atomic_read(&console_kthreads_active)); + } + EXPORT_SYMBOL(is_console_locked); + +@@ -2636,12 +2796,9 @@ EXPORT_SYMBOL(is_console_locked); + * + * Requires the console_lock. + */ +-static inline bool console_is_usable(struct console *con) ++static inline bool __console_is_usable(short flags) + { +- if (!(con->flags & CON_ENABLED)) +- return false; +- +- if (!con->write) ++ if (!(flags & CON_ENABLED)) + return false; + + /* +@@ -2650,15 +2807,43 @@ static inline bool console_is_usable(struct console *con) + * cope (CON_ANYTIME) don't call them until this CPU is officially up. + */ + if (!cpu_online(raw_smp_processor_id()) && +- !(con->flags & CON_ANYTIME)) ++ !(flags & CON_ANYTIME)) + return false; + + return true; + } + ++/* ++ * Check if the given console is currently capable and allowed to print ++ * records. ++ * ++ * Requires holding the console_lock. ++ */ ++static inline bool console_is_usable(struct console *con) ++{ ++ if (!con->write) ++ return false; ++ ++ return __console_is_usable(con->flags); ++} ++ + static void __console_unlock(void) + { +- console_locked = 0; ++ /* ++ * Depending on whether console_lock() or console_trylock() was used, ++ * appropriately allow the kthread printers to continue. ++ */ ++ if (console_kthreads_blocked) ++ console_kthreads_unblock(); ++ else ++ console_kthreads_atomic_unblock(); ++ ++ /* ++ * New records may have arrived while the console was locked. ++ * Wake the kthread printers to print them. ++ */ ++ wake_up_klogd(); ++ + up_console_sem(); + } + +@@ -2676,17 +2861,19 @@ static void __console_unlock(void) + * + * @handover will be set to true if a printk waiter has taken over the + * console_lock, in which case the caller is no longer holding the +- * console_lock. Otherwise it is set to false. ++ * console_lock. Otherwise it is set to false. A NULL pointer may be provided ++ * to disable allowing the console_lock to be taken over by a printk waiter. + * + * Returns false if the given console has no next record to print, otherwise + * true. + * +- * Requires the console_lock. ++ * Requires the console_lock if @handover is non-NULL. ++ * Requires con->lock otherwise. + */ +-static bool console_emit_next_record(struct console *con, char *text, char *ext_text, +- char *dropped_text, bool *handover) ++static bool __console_emit_next_record(struct console *con, char *text, char *ext_text, ++ char *dropped_text, bool *handover) + { +- static int panic_console_dropped; ++ static atomic_t panic_console_dropped = ATOMIC_INIT(0); + struct printk_info info; + struct printk_record r; + unsigned long flags; +@@ -2695,7 +2882,8 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_ + + prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX); + +- *handover = false; ++ if (handover) ++ *handover = false; + + if (!prb_read_valid(prb, con->seq, &r)) + return false; +@@ -2703,7 +2891,8 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_ + if (con->seq != r.info->seq) { + con->dropped += r.info->seq - con->seq; + con->seq = r.info->seq; +- if (panic_in_progress() && panic_console_dropped++ > 10) { ++ if (panic_in_progress() && ++ atomic_fetch_inc_relaxed(&panic_console_dropped) > 10) { + suppress_panic_printk = 1; + pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n"); + } +@@ -2725,31 +2914,61 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_ + len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time); + } + +- /* +- * 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(); ++ if (handover) { ++ /* ++ * 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(); ++ ++ /* don't trace irqsoff print latency */ ++ stop_critical_timings(); ++ } + +- stop_critical_timings(); /* don't trace print latency */ + call_console_driver(con, write_text, len, dropped_text); +- start_critical_timings(); + + con->seq++; + +- *handover = console_lock_spinning_disable_and_check(); +- printk_safe_exit_irqrestore(flags); ++ if (handover) { ++ start_critical_timings(); ++ *handover = console_lock_spinning_disable_and_check(); ++ printk_safe_exit_irqrestore(flags); ++ } + skip: + return true; + } + ++/* ++ * Print a record for a given console, but allow another printk() caller to ++ * take over the console_lock and continue printing. ++ * ++ * Requires the console_lock, but depending on @handover after the call, the ++ * caller may no longer have the console_lock. ++ * ++ * See __console_emit_next_record() for argument and return details. ++ */ ++static bool console_emit_next_record_transferable(struct console *con, char *text, char *ext_text, ++ char *dropped_text, bool *handover) ++{ ++ /* ++ * Handovers are only supported if threaded printers are atomically ++ * blocked. The context taking over the console_lock may be atomic. ++ */ ++ if (!console_kthreads_atomically_blocked()) { ++ *handover = false; ++ handover = NULL; ++ } ++ ++ return __console_emit_next_record(con, text, ext_text, dropped_text, handover); ++} ++ + /* + * Print out all remaining records to all consoles. + * +@@ -2768,8 +2987,8 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_ + * were flushed to all usable consoles. A returned false informs the caller + * that everything was not flushed (either there were no usable consoles or + * another context has taken over printing or it is a panic situation and this +- * is not the panic CPU). Regardless the reason, the caller should assume it +- * is not useful to immediately try again. ++ * is not the panic CPU or direct printing is not preferred). Regardless the ++ * reason, the caller should assume it is not useful to immediately try again. + * + * Requires the console_lock. + */ +@@ -2786,6 +3005,10 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove + *handover = false; + + do { ++ /* Let the kthread printers do the work if they can. */ ++ if (!allow_direct_printing()) ++ return false; ++ + any_progress = false; + + for_each_console(con) { +@@ -2797,13 +3020,11 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove + + if (con->flags & CON_EXTENDED) { + /* Extended consoles do not print "dropped messages". */ +- progress = console_emit_next_record(con, &text[0], +- &ext_text[0], NULL, +- handover); ++ progress = console_emit_next_record_transferable(con, &text[0], ++ &ext_text[0], NULL, handover); + } else { +- progress = console_emit_next_record(con, &text[0], +- NULL, &dropped_text[0], +- handover); ++ progress = console_emit_next_record_transferable(con, &text[0], ++ NULL, &dropped_text[0], handover); + } + if (*handover) + return false; +@@ -2918,10 +3139,13 @@ void console_unblank(void) + if (oops_in_progress) { + if (down_trylock_console_sem() != 0) + return; ++ if (!console_kthreads_atomic_tryblock()) { ++ up_console_sem(); ++ return; ++ } + } else + console_lock(); + +- console_locked = 1; + console_may_schedule = 0; + for_each_console(c) + if ((c->flags & CON_ENABLED) && c->unblank) +@@ -3197,6 +3421,10 @@ void register_console(struct console *newcon) + } + + newcon->dropped = 0; ++ newcon->thread = NULL; ++ newcon->blocked = true; ++ mutex_init(&newcon->lock); ++ + if (newcon->flags & CON_PRINTBUFFER) { + /* Get a consistent copy of @syslog_seq. */ + mutex_lock(&syslog_lock); +@@ -3206,6 +3434,10 @@ void register_console(struct console *newcon) + /* Begin with next message. */ + newcon->seq = prb_next_seq(prb); + } ++ ++ if (printk_kthreads_available) ++ printk_start_kthread(newcon); ++ + console_unlock(); + console_sysfs_notify(); + +@@ -3229,6 +3461,7 @@ EXPORT_SYMBOL(register_console); + + int unregister_console(struct console *console) + { ++ struct task_struct *thd; + struct console *con; + int res; + +@@ -3266,7 +3499,20 @@ int unregister_console(struct console *console) + console_drivers->flags |= CON_CONSDEV; + + console->flags &= ~CON_ENABLED; ++ ++ /* ++ * console->thread can only be cleared under the console lock. But ++ * stopping the thread must be done without the console lock. The ++ * task that clears @thread is the task that stops the kthread. ++ */ ++ thd = console->thread; ++ console->thread = NULL; ++ + console_unlock(); ++ ++ if (thd) ++ kthread_stop(thd); ++ + console_sysfs_notify(); + + if (console->exit) +@@ -3362,6 +3608,20 @@ static int __init printk_late_init(void) + } + late_initcall(printk_late_init); + ++static int __init printk_activate_kthreads(void) ++{ ++ struct console *con; ++ ++ console_lock(); ++ printk_kthreads_available = true; ++ for_each_console(con) ++ printk_start_kthread(con); ++ console_unlock(); ++ ++ return 0; ++} ++early_initcall(printk_activate_kthreads); ++ + #if defined CONFIG_PRINTK + /* If @con is specified, only wait for that console. Otherwise wait for all. */ + static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) +@@ -3444,11 +3704,208 @@ static bool pr_flush(int timeout_ms, bool reset_on_progress) + return __pr_flush(NULL, timeout_ms, reset_on_progress); + } + ++static void __printk_fallback_preferred_direct(void) ++{ ++ printk_prefer_direct_enter(); ++ pr_err("falling back to preferred direct printing\n"); ++ printk_kthreads_available = false; ++} ++ ++/* ++ * Enter preferred direct printing, but never exit. Mark console threads as ++ * unavailable. The system is then forever in preferred direct printing and ++ * any printing threads will exit. ++ * ++ * Must *not* be called under console_lock. Use ++ * __printk_fallback_preferred_direct() if already holding console_lock. ++ */ ++static void printk_fallback_preferred_direct(void) ++{ ++ console_lock(); ++ __printk_fallback_preferred_direct(); ++ console_unlock(); ++} ++ ++/* ++ * Print a record for a given console, not allowing another printk() caller ++ * to take over. This is appropriate for contexts that do not have the ++ * console_lock. ++ * ++ * See __console_emit_next_record() for argument and return details. ++ */ ++static bool console_emit_next_record(struct console *con, char *text, char *ext_text, ++ char *dropped_text) ++{ ++ return __console_emit_next_record(con, text, ext_text, dropped_text, NULL); ++} ++ ++static bool printer_should_wake(struct console *con, u64 seq) ++{ ++ short flags; ++ ++ if (kthread_should_stop() || !printk_kthreads_available) ++ return true; ++ ++ if (con->blocked || ++ console_kthreads_atomically_blocked() || ++ block_console_kthreads || ++ system_state > SYSTEM_RUNNING || ++ oops_in_progress) { ++ return false; ++ } ++ ++ /* ++ * This is an unsafe read from con->flags, but a false positive is ++ * not a problem. Worst case it would allow the printer to wake up ++ * although it is disabled. But the printer will notice that when ++ * attempting to print and instead go back to sleep. ++ */ ++ flags = data_race(READ_ONCE(con->flags)); ++ ++ if (!__console_is_usable(flags)) ++ return false; ++ ++ return prb_read_valid(prb, seq, NULL); ++} ++ ++static int printk_kthread_func(void *data) ++{ ++ struct console *con = data; ++ char *dropped_text = NULL; ++ char *ext_text = NULL; ++ u64 seq = 0; ++ char *text; ++ int error; ++ ++ text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL); ++ if (!text) { ++ con_printk(KERN_ERR, con, "failed to allocate text buffer\n"); ++ printk_fallback_preferred_direct(); ++ goto out; ++ } ++ ++ if (con->flags & CON_EXTENDED) { ++ ext_text = kmalloc(CONSOLE_EXT_LOG_MAX, GFP_KERNEL); ++ if (!ext_text) { ++ con_printk(KERN_ERR, con, "failed to allocate ext_text buffer\n"); ++ printk_fallback_preferred_direct(); ++ goto out; ++ } ++ } else { ++ dropped_text = kmalloc(DROPPED_TEXT_MAX, GFP_KERNEL); ++ if (!dropped_text) { ++ con_printk(KERN_ERR, con, "failed to allocate dropped_text buffer\n"); ++ printk_fallback_preferred_direct(); ++ goto out; ++ } ++ } ++ ++ con_printk(KERN_INFO, con, "printing thread started\n"); ++ for (;;) { ++ /* ++ * Guarantee this task is visible on the waitqueue before ++ * checking the wake condition. ++ * ++ * The full memory barrier within set_current_state() of ++ * prepare_to_wait_event() pairs with the full memory barrier ++ * within wq_has_sleeper(). ++ * ++ * This pairs with __wake_up_klogd:A. ++ */ ++ error = wait_event_interruptible(log_wait, ++ printer_should_wake(con, seq)); /* LMM(printk_kthread_func:A) */ ++ ++ if (kthread_should_stop() || !printk_kthreads_available) ++ break; ++ ++ if (error) ++ continue; ++ ++ error = mutex_lock_interruptible(&con->lock); ++ if (error) ++ continue; ++ ++ if (con->blocked || ++ !console_kthread_printing_tryenter()) { ++ /* Another context has locked the console_lock. */ ++ mutex_unlock(&con->lock); ++ continue; ++ } ++ ++ /* ++ * Although this context has not locked the console_lock, it ++ * is known that the console_lock is not locked and it is not ++ * possible for any other context to lock the console_lock. ++ * Therefore it is safe to read con->flags. ++ */ ++ ++ if (!__console_is_usable(con->flags)) { ++ console_kthread_printing_exit(); ++ mutex_unlock(&con->lock); ++ continue; ++ } ++ ++ /* ++ * Even though the printk kthread is always preemptible, it is ++ * still not allowed to call cond_resched() from within ++ * console drivers. The task may become non-preemptible in the ++ * console driver call chain. For example, vt_console_print() ++ * takes a spinlock and then can call into fbcon_redraw(), ++ * which can conditionally invoke cond_resched(). ++ */ ++ console_may_schedule = 0; ++ console_emit_next_record(con, text, ext_text, dropped_text); ++ ++ seq = con->seq; ++ ++ console_kthread_printing_exit(); ++ ++ mutex_unlock(&con->lock); ++ } ++ ++ con_printk(KERN_INFO, con, "printing thread stopped\n"); ++out: ++ kfree(dropped_text); ++ kfree(ext_text); ++ kfree(text); ++ ++ console_lock(); ++ /* ++ * If this kthread is being stopped by another task, con->thread will ++ * already be NULL. That is fine. The important thing is that it is ++ * NULL after the kthread exits. ++ */ ++ con->thread = NULL; ++ console_unlock(); ++ ++ return 0; ++} ++ ++/* Must be called under console_lock. */ ++static void printk_start_kthread(struct console *con) ++{ ++ /* ++ * Do not start a kthread if there is no write() callback. The ++ * kthreads assume the write() callback exists. ++ */ ++ if (!con->write) ++ return; ++ ++ con->thread = kthread_run(printk_kthread_func, con, ++ "pr/%s%d", con->name, con->index); ++ if (IS_ERR(con->thread)) { ++ con->thread = NULL; ++ con_printk(KERN_ERR, con, "unable to start printing thread\n"); ++ __printk_fallback_preferred_direct(); ++ return; ++ } ++} ++ + /* + * Delayed printk version, for scheduler-internal messages: + */ +-#define PRINTK_PENDING_WAKEUP 0x01 +-#define PRINTK_PENDING_OUTPUT 0x02 ++#define PRINTK_PENDING_WAKEUP 0x01 ++#define PRINTK_PENDING_DIRECT_OUTPUT 0x02 + + static DEFINE_PER_CPU(int, printk_pending); + +@@ -3456,10 +3913,14 @@ static void wake_up_klogd_work_func(struct irq_work *irq_work) + { + int pending = this_cpu_xchg(printk_pending, 0); + +- if (pending & PRINTK_PENDING_OUTPUT) { ++ if (pending & PRINTK_PENDING_DIRECT_OUTPUT) { ++ printk_prefer_direct_enter(); ++ + /* If trylock fails, someone else is doing the printing */ + if (console_trylock()) + console_unlock(); ++ ++ printk_prefer_direct_exit(); + } + + if (pending & PRINTK_PENDING_WAKEUP) +@@ -3484,10 +3945,11 @@ static void __wake_up_klogd(int val) + * prepare_to_wait_event(), which is called after ___wait_event() adds + * the waiter but before it has checked the wait condition. + * +- * This pairs with devkmsg_read:A and syslog_print:A. ++ * This pairs with devkmsg_read:A, syslog_print:A, and ++ * printk_kthread_func:A. + */ + if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */ +- (val & PRINTK_PENDING_OUTPUT)) { ++ (val & PRINTK_PENDING_DIRECT_OUTPUT)) { + this_cpu_or(printk_pending, val); + irq_work_queue(this_cpu_ptr(&wake_up_klogd_work)); + } +@@ -3527,7 +3989,17 @@ void defer_console_output(void) + * New messages may have been added directly to the ringbuffer + * using vprintk_store(), so wake any waiters as well. + */ +- __wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT); ++ int val = PRINTK_PENDING_WAKEUP; ++ ++ /* ++ * Make sure that some context will print the messages when direct ++ * printing is allowed. This happens in situations when the kthreads ++ * may not be as reliable or perhaps unusable. ++ */ ++ if (allow_direct_printing()) ++ val |= PRINTK_PENDING_DIRECT_OUTPUT; ++ ++ __wake_up_klogd(val); + } + + void printk_trigger_flush(void) +diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c +index 6d10927a07d8..8e8fd2fb0a5b 100644 +--- a/kernel/printk/printk_safe.c ++++ b/kernel/printk/printk_safe.c +@@ -8,7 +8,9 @@ + #include <linux/smp.h> + #include <linux/cpumask.h> + #include <linux/printk.h> ++#include <linux/console.h> + #include <linux/kprobes.h> ++#include <linux/delay.h> + + #include "internal.h" + +@@ -45,3 +47,33 @@ asmlinkage int vprintk(const char *fmt, va_list args) + return vprintk_default(fmt, args); + } + EXPORT_SYMBOL(vprintk); ++ ++/** ++ * try_block_console_kthreads() - Try to block console kthreads and ++ * make the global console_lock() avaialble ++ * ++ * @timeout_ms: The maximum time (in ms) to wait. ++ * ++ * Prevent console kthreads from starting processing new messages. Wait ++ * until the global console_lock() become available. ++ * ++ * Context: Can be called in any context. ++ */ ++void try_block_console_kthreads(int timeout_ms) ++{ ++ block_console_kthreads = true; ++ ++ /* Do not wait when the console lock could not be safely taken. */ ++ if (this_cpu_read(printk_context) || in_nmi()) ++ return; ++ ++ while (timeout_ms > 0) { ++ if (console_trylock()) { ++ console_unlock(); ++ return; ++ } ++ ++ udelay(1000); ++ timeout_ms -= 1; ++ } ++} +diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h +index 7d15b5b5a235..7b411d663e8f 100644 +--- a/kernel/rcu/tree_stall.h ++++ b/kernel/rcu/tree_stall.h +@@ -648,6 +648,7 @@ static void print_cpu_stall(unsigned long gps) + * See Documentation/RCU/stallwarn.rst for info on how to debug + * RCU CPU stall warnings. + */ ++ printk_prefer_direct_enter(); + trace_rcu_stall_warning(rcu_state.name, TPS("SelfDetected")); + pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name); + raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags); +@@ -682,6 +683,7 @@ static void print_cpu_stall(unsigned long gps) + */ + set_tsk_need_resched(current); + set_preempt_need_resched(); ++ printk_prefer_direct_exit(); + } + + static void check_cpu_stall(struct rcu_data *rdp) +diff --git a/kernel/reboot.c b/kernel/reboot.c +index 6ebef11c8876..23a8cfed1a72 100644 +--- a/kernel/reboot.c ++++ b/kernel/reboot.c +@@ -83,6 +83,7 @@ void kernel_restart_prepare(char *cmd) + { + blocking_notifier_call_chain(&reboot_notifier_list, SYS_RESTART, cmd); + system_state = SYSTEM_RESTART; ++ try_block_console_kthreads(10000); + usermodehelper_disable(); + device_shutdown(); + } +@@ -283,6 +284,7 @@ static void kernel_shutdown_prepare(enum system_states state) + blocking_notifier_call_chain(&reboot_notifier_list, + (state == SYSTEM_HALT) ? SYS_HALT : SYS_POWER_OFF, NULL); + system_state = state; ++ try_block_console_kthreads(10000); + usermodehelper_disable(); + device_shutdown(); + } +@@ -837,9 +839,11 @@ static int __orderly_reboot(void) + ret = run_cmd(reboot_cmd); + + if (ret) { ++ printk_prefer_direct_enter(); + pr_warn("Failed to start orderly reboot: forcing the issue\n"); + emergency_sync(); + kernel_restart(NULL); ++ printk_prefer_direct_exit(); + } + + return ret; +@@ -852,6 +856,7 @@ static int __orderly_poweroff(bool force) + ret = run_cmd(poweroff_cmd); + + if (ret && force) { ++ printk_prefer_direct_enter(); + pr_warn("Failed to start orderly shutdown: forcing the issue\n"); + + /* +@@ -861,6 +866,7 @@ static int __orderly_poweroff(bool force) + */ + emergency_sync(); + kernel_power_off(); ++ printk_prefer_direct_exit(); + } + + return ret; +@@ -918,6 +924,8 @@ EXPORT_SYMBOL_GPL(orderly_reboot); + */ + static void hw_failure_emergency_poweroff_func(struct work_struct *work) + { ++ printk_prefer_direct_enter(); ++ + /* + * We have reached here after the emergency shutdown waiting period has + * expired. This means orderly_poweroff has not been able to shut off +@@ -934,6 +942,8 @@ static void hw_failure_emergency_poweroff_func(struct work_struct *work) + */ + pr_emerg("Hardware protection shutdown failed. Trying emergency restart\n"); + emergency_restart(); ++ ++ printk_prefer_direct_exit(); + } + + static DECLARE_DELAYED_WORK(hw_failure_emergency_poweroff_work, +@@ -972,11 +982,13 @@ void hw_protection_shutdown(const char *reason, int ms_until_forced) + { + static atomic_t allow_proceed = ATOMIC_INIT(1); + ++ printk_prefer_direct_enter(); ++ + pr_emerg("HARDWARE PROTECTION shutdown (%s)\n", reason); + + /* Shutdown should be initiated only once. */ + if (!atomic_dec_and_test(&allow_proceed)) +- return; ++ goto out; + + /* + * Queue a backup emergency shutdown in the event of +@@ -984,6 +996,8 @@ void hw_protection_shutdown(const char *reason, int ms_until_forced) + */ + hw_failure_emergency_poweroff(ms_until_forced); + orderly_poweroff(true); ++out: ++ printk_prefer_direct_exit(); + } + EXPORT_SYMBOL_GPL(hw_protection_shutdown); + +diff --git a/kernel/watchdog.c b/kernel/watchdog.c +index 45693fb3e08d..f366008298ac 100644 +--- a/kernel/watchdog.c ++++ b/kernel/watchdog.c +@@ -431,6 +431,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) + /* Start period for the next softlockup warning. */ + update_report_ts(); + ++ printk_prefer_direct_enter(); ++ + pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", + smp_processor_id(), duration, + current->comm, task_pid_nr(current)); +@@ -449,6 +451,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) + add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK); + if (softlockup_panic) + panic("softlockup: hung tasks"); ++ ++ printk_prefer_direct_exit(); + } + + return HRTIMER_RESTART; +diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c +index 1e8a49dc956e..7c977b945c92 100644 +--- a/kernel/watchdog_hld.c ++++ b/kernel/watchdog_hld.c +@@ -135,6 +135,8 @@ static void watchdog_overflow_callback(struct perf_event *event, + if (__this_cpu_read(hard_watchdog_warn) == true) + return; + ++ printk_prefer_direct_enter(); ++ + pr_emerg("Watchdog detected hard LOCKUP on cpu %d\n", + this_cpu); + print_modules(); +@@ -155,6 +157,8 @@ static void watchdog_overflow_callback(struct perf_event *event, + if (hardlockup_panic) + nmi_panic(regs, "Hard LOCKUP"); + ++ printk_prefer_direct_exit(); ++ + __this_cpu_write(hard_watchdog_warn, true); + return; + } +-- +2.43.0 + |