diff options
Diffstat (limited to 'debian/patches-rt/0020-printk-add-infrastucture-for-atomic-consoles.patch')
| -rw-r--r-- | debian/patches-rt/0020-printk-add-infrastucture-for-atomic-consoles.patch | 608 |
1 files changed, 608 insertions, 0 deletions
diff --git a/debian/patches-rt/0020-printk-add-infrastucture-for-atomic-consoles.patch b/debian/patches-rt/0020-printk-add-infrastucture-for-atomic-consoles.patch new file mode 100644 index 000000000..b86b20007 --- /dev/null +++ b/debian/patches-rt/0020-printk-add-infrastucture-for-atomic-consoles.patch @@ -0,0 +1,608 @@ +From 18343f23a5f1d466a0c74806983066efba932d5d Mon Sep 17 00:00:00 2001 +From: John Ogness <john.ogness@linutronix.de> +Date: Fri, 4 Feb 2022 16:01:17 +0106 +Subject: [PATCH 20/62] printk: add infrastucture for atomic consoles +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.1/older/patches-6.1.69-rt21.tar.xz + +Many times it is not possible to see the console output on +panic because printing threads cannot be scheduled and/or the +console is already taken and forcibly overtaking/busting the +locks does provide the hoped results. + +Introduce a new infrastructure to support "atomic consoles". +A new optional callback in struct console, write_atomic(), is +available for consoles to provide an implemention for writing +console messages. The implementation must be NMI safe if they +can run on an architecture where NMIs exist. + +Console drivers implementing the write_atomic() callback must +also select CONFIG_HAVE_ATOMIC_CONSOLE in order to enable the +atomic console code within the printk subsystem. + +If atomic consoles are available, panic() will flush the kernel +log only to the atomic consoles (before busting spinlocks). +Afterwards, panic() will continue as before, which includes +attempting to flush the other (non-atomic) consoles. + +Signed-off-by: John Ogness <john.ogness@linutronix.de> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + include/linux/console.h | 16 ++- + init/Kconfig | 4 + + kernel/panic.c | 6 +- + kernel/printk/printk.c | 293 ++++++++++++++++++++++++++++++++++++---- + 4 files changed, 290 insertions(+), 29 deletions(-) + +diff --git a/include/linux/console.h b/include/linux/console.h +index 143653090c48..8a813cbaf928 100644 +--- a/include/linux/console.h ++++ b/include/linux/console.h +@@ -138,9 +138,19 @@ static inline int con_debug_leave(void) + #define CON_BRL (32) /* Used for a braille device */ + #define CON_EXTENDED (64) /* Use the extended output format a la /dev/kmsg */ + ++#ifdef CONFIG_HAVE_ATOMIC_CONSOLE ++struct console_atomic_data { ++ u64 seq; ++ char *text; ++ char *ext_text; ++ char *dropped_text; ++}; ++#endif ++ + struct console { + char name[16]; + void (*write)(struct console *, const char *, unsigned); ++ void (*write_atomic)(struct console *, const char *, unsigned); + int (*read)(struct console *, char *, unsigned); + struct tty_driver *(*device)(struct console *, int *); + void (*unblank)(void); +@@ -153,7 +163,10 @@ struct console { + uint ispeed; + uint ospeed; + u64 seq; +- unsigned long dropped; ++ atomic_long_t dropped; ++#ifdef CONFIG_HAVE_ATOMIC_CONSOLE ++ struct console_atomic_data *atomic_data; ++#endif + struct task_struct *thread; + bool blocked; + +@@ -184,6 +197,7 @@ extern int console_set_on_cmdline; + extern struct console *early_console; + + enum con_flush_mode { ++ CONSOLE_ATOMIC_FLUSH_PENDING, + CONSOLE_FLUSH_PENDING, + CONSOLE_REPLAY_ALL, + }; +diff --git a/init/Kconfig b/init/Kconfig +index de255842f5d0..d45312780b3a 100644 +--- a/init/Kconfig ++++ b/init/Kconfig +@@ -1582,6 +1582,10 @@ config PRINTK + very difficult to diagnose system problems, saying N here is + strongly discouraged. + ++config HAVE_ATOMIC_CONSOLE ++ bool ++ default n ++ + config BUG + bool "BUG() support" if EXPERT + default y +diff --git a/kernel/panic.c b/kernel/panic.c +index 88cd873c7c30..97cc495d95f8 100644 +--- a/kernel/panic.c ++++ b/kernel/panic.c +@@ -322,7 +322,6 @@ void panic(const char *fmt, ...) + panic_smp_self_stop(); + + console_verbose(); +- bust_spinlocks(1); + va_start(args, fmt); + len = vscnprintf(buf, sizeof(buf), fmt, args); + va_end(args); +@@ -339,6 +338,11 @@ void panic(const char *fmt, ...) + dump_stack(); + #endif + ++ /* If atomic consoles are available, flush the kernel log. */ ++ console_flush_on_panic(CONSOLE_ATOMIC_FLUSH_PENDING); ++ ++ bust_spinlocks(1); ++ + /* + * If kgdb is enabled, give it a chance to run before we stop all + * the other CPUs or else we won't be able to debug processes left +diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c +index e9f9b66608a0..73b1727087c7 100644 +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -44,6 +44,7 @@ + #include <linux/irq_work.h> + #include <linux/ctype.h> + #include <linux/uio.h> ++#include <linux/clocksource.h> + #include <linux/sched/clock.h> + #include <linux/sched/debug.h> + #include <linux/sched/task_stack.h> +@@ -2060,19 +2061,28 @@ static int console_trylock_spinning(void) + * dropped, a dropped message will be written out first. + */ + static void call_console_driver(struct console *con, const char *text, size_t len, +- char *dropped_text) ++ char *dropped_text, bool atomic_printing) + { ++ unsigned long dropped = 0; + size_t dropped_len; + +- if (con->dropped && dropped_text) { ++ if (dropped_text) ++ dropped = atomic_long_xchg_relaxed(&con->dropped, 0); ++ ++ if (dropped) { + dropped_len = snprintf(dropped_text, DROPPED_TEXT_MAX, + "** %lu printk messages dropped **\n", +- con->dropped); +- con->dropped = 0; +- con->write(con, dropped_text, dropped_len); ++ dropped); ++ if (atomic_printing) ++ con->write_atomic(con, dropped_text, dropped_len); ++ else ++ con->write(con, dropped_text, dropped_len); + } + +- con->write(con, text, len); ++ if (atomic_printing) ++ con->write_atomic(con, text, len); ++ else ++ con->write(con, text, len); + } + + /* +@@ -2430,6 +2440,76 @@ asmlinkage __visible int _printk(const char *fmt, ...) + } + EXPORT_SYMBOL(_printk); + ++#ifdef CONFIG_HAVE_ATOMIC_CONSOLE ++static void __free_atomic_data(struct console_atomic_data *d) ++{ ++ kfree(d->text); ++ kfree(d->ext_text); ++ kfree(d->dropped_text); ++} ++ ++static void free_atomic_data(struct console_atomic_data *d) ++{ ++ int count = 1; ++ int i; ++ ++ if (!d) ++ return; ++ ++#ifdef CONFIG_HAVE_NMI ++ count = 2; ++#endif ++ ++ for (i = 0; i < count; i++) ++ __free_atomic_data(&d[i]); ++ kfree(d); ++} ++ ++static int __alloc_atomic_data(struct console_atomic_data *d, short flags) ++{ ++ d->text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL); ++ if (!d->text) ++ return -1; ++ ++ if (flags & CON_EXTENDED) { ++ d->ext_text = kmalloc(CONSOLE_EXT_LOG_MAX, GFP_KERNEL); ++ if (!d->ext_text) ++ return -1; ++ } else { ++ d->dropped_text = kmalloc(DROPPED_TEXT_MAX, GFP_KERNEL); ++ if (!d->dropped_text) ++ return -1; ++ } ++ ++ return 0; ++} ++ ++static struct console_atomic_data *alloc_atomic_data(short flags) ++{ ++ struct console_atomic_data *d; ++ int count = 1; ++ int i; ++ ++#ifdef CONFIG_HAVE_NMI ++ count = 2; ++#endif ++ ++ d = kzalloc(sizeof(*d) * count, GFP_KERNEL); ++ if (!d) ++ goto err_out; ++ ++ for (i = 0; i < count; i++) { ++ if (__alloc_atomic_data(&d[i], flags) != 0) ++ goto err_out; ++ } ++ ++ return d; ++err_out: ++ free_atomic_data(d); ++ return NULL; ++} ++#endif /* CONFIG_HAVE_ATOMIC_CONSOLE */ ++ + 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); + +@@ -2445,6 +2525,8 @@ static void printk_start_kthread(struct console *con); + #define prb_first_valid_seq(rb) 0 + #define prb_next_seq(rb) 0 + ++#define free_atomic_data(d) ++ + static u64 syslog_seq; + + static size_t record_print_text(const struct printk_record *r, +@@ -2463,7 +2545,7 @@ static ssize_t msg_print_ext_body(char *buf, size_t size, + static void console_lock_spinning_enable(void) { } + static int console_lock_spinning_disable_and_check(void) { return 0; } + static void call_console_driver(struct console *con, const char *text, size_t len, +- char *dropped_text) ++ char *dropped_text, bool atomic_printing) + { + } + static bool suppress_message_printing(int level) { return false; } +@@ -2819,10 +2901,20 @@ static inline bool __console_is_usable(short flags) + * + * Requires holding the console_lock. + */ +-static inline bool console_is_usable(struct console *con) ++static inline bool console_is_usable(struct console *con, bool atomic_printing) + { +- if (!con->write) ++ if (atomic_printing) { ++#ifdef CONFIG_HAVE_ATOMIC_CONSOLE ++ if (!con->write_atomic) ++ return false; ++ if (!con->atomic_data) ++ return false; ++#else ++ return false; ++#endif ++ } else if (!con->write) { + return false; ++ } + + return __console_is_usable(con->flags); + } +@@ -2847,6 +2939,66 @@ static void __console_unlock(void) + up_console_sem(); + } + ++static u64 read_console_seq(struct console *con) ++{ ++#ifdef CONFIG_HAVE_ATOMIC_CONSOLE ++ unsigned long flags; ++ u64 seq2; ++ u64 seq; ++ ++ if (!con->atomic_data) ++ return con->seq; ++ ++ printk_cpu_sync_get_irqsave(flags); ++ ++ seq = con->seq; ++ seq2 = con->atomic_data[0].seq; ++ if (seq2 > seq) ++ seq = seq2; ++#ifdef CONFIG_HAVE_NMI ++ seq2 = con->atomic_data[1].seq; ++ if (seq2 > seq) ++ seq = seq2; ++#endif ++ ++ printk_cpu_sync_put_irqrestore(flags); ++ ++ return seq; ++#else /* CONFIG_HAVE_ATOMIC_CONSOLE */ ++ return con->seq; ++#endif ++} ++ ++static void write_console_seq(struct console *con, u64 val, bool atomic_printing) ++{ ++#ifdef CONFIG_HAVE_ATOMIC_CONSOLE ++ unsigned long flags; ++ u64 *seq; ++ ++ if (!con->atomic_data) { ++ con->seq = val; ++ return; ++ } ++ ++ printk_cpu_sync_get_irqsave(flags); ++ ++ if (atomic_printing) { ++ seq = &con->atomic_data[0].seq; ++#ifdef CONFIG_HAVE_NMI ++ if (in_nmi()) ++ seq = &con->atomic_data[1].seq; ++#endif ++ } else { ++ seq = &con->seq; ++ } ++ *seq = val; ++ ++ printk_cpu_sync_put_irqrestore(flags); ++#else /* CONFIG_HAVE_ATOMIC_CONSOLE */ ++ con->seq = val; ++#endif ++} ++ + /* + * Print one record for the given console. The record printed is whatever + * record is the next available record for the given console. +@@ -2859,6 +3011,8 @@ static void __console_unlock(void) + * If dropped messages should be printed, @dropped_text is a buffer of size + * DROPPED_TEXT_MAX. Otherwise @dropped_text must be NULL. + * ++ * @atomic_printing specifies if atomic printing should be used. ++ * + * @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. A NULL pointer may be provided +@@ -2871,7 +3025,8 @@ static void __console_unlock(void) + * Requires con->lock otherwise. + */ + static bool __console_emit_next_record(struct console *con, char *text, char *ext_text, +- char *dropped_text, bool *handover) ++ char *dropped_text, bool atomic_printing, ++ bool *handover) + { + static atomic_t panic_console_dropped = ATOMIC_INIT(0); + struct printk_info info; +@@ -2879,18 +3034,22 @@ static bool __console_emit_next_record(struct console *con, char *text, char *ex + unsigned long flags; + char *write_text; + size_t len; ++ u64 seq; + + prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX); + + if (handover) + *handover = false; + +- if (!prb_read_valid(prb, con->seq, &r)) ++ seq = read_console_seq(con); ++ ++ if (!prb_read_valid(prb, seq, &r)) + return false; + +- if (con->seq != r.info->seq) { +- con->dropped += r.info->seq - con->seq; +- con->seq = r.info->seq; ++ if (seq != r.info->seq) { ++ atomic_long_add((unsigned long)(r.info->seq - seq), &con->dropped); ++ write_console_seq(con, r.info->seq, atomic_printing); ++ seq = r.info->seq; + if (panic_in_progress() && + atomic_fetch_inc_relaxed(&panic_console_dropped) > 10) { + suppress_panic_printk = 1; +@@ -2900,7 +3059,7 @@ static bool __console_emit_next_record(struct console *con, char *text, char *ex + + /* Skip record that has level above the console loglevel. */ + if (suppress_message_printing(r.info->level)) { +- con->seq++; ++ write_console_seq(con, seq + 1, atomic_printing); + goto skip; + } + +@@ -2932,9 +3091,9 @@ static bool __console_emit_next_record(struct console *con, char *text, char *ex + stop_critical_timings(); + } + +- call_console_driver(con, write_text, len, dropped_text); ++ call_console_driver(con, write_text, len, dropped_text, atomic_printing); + +- con->seq++; ++ write_console_seq(con, seq + 1, atomic_printing); + + if (handover) { + start_critical_timings(); +@@ -2966,7 +3125,7 @@ static bool console_emit_next_record_transferable(struct console *con, char *tex + handover = NULL; + } + +- return __console_emit_next_record(con, text, ext_text, dropped_text, handover); ++ return __console_emit_next_record(con, text, ext_text, dropped_text, false, handover); + } + + /* +@@ -3014,7 +3173,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove + for_each_console(con) { + bool progress; + +- if (!console_is_usable(con)) ++ if (!console_is_usable(con, false)) + continue; + any_usable = true; + +@@ -3049,6 +3208,68 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove + return any_usable; + } + ++#if defined(CONFIG_HAVE_ATOMIC_CONSOLE) && defined(CONFIG_PRINTK) ++static bool console_emit_next_record(struct console *con, char *text, char *ext_text, ++ char *dropped_text, bool atomic_printing); ++ ++static void atomic_console_flush_all(void) ++{ ++ unsigned long flags; ++ struct console *con; ++ bool any_progress; ++ int index = 0; ++ ++ if (console_suspended) ++ return; ++ ++#ifdef CONFIG_HAVE_NMI ++ if (in_nmi()) ++ index = 1; ++#endif ++ ++ printk_cpu_sync_get_irqsave(flags); ++ ++ do { ++ any_progress = false; ++ ++ for_each_console(con) { ++ bool progress; ++ ++ if (!console_is_usable(con, true)) ++ continue; ++ ++ if (con->flags & CON_EXTENDED) { ++ /* Extended consoles do not print "dropped messages". */ ++ progress = console_emit_next_record(con, ++ &con->atomic_data->text[index], ++ &con->atomic_data->ext_text[index], ++ NULL, ++ true); ++ } else { ++ progress = console_emit_next_record(con, ++ &con->atomic_data->text[index], ++ NULL, ++ &con->atomic_data->dropped_text[index], ++ true); ++ } ++ ++ if (!progress) ++ continue; ++ any_progress = true; ++ ++ touch_softlockup_watchdog_sync(); ++ clocksource_touch_watchdog(); ++ rcu_cpu_stall_reset(); ++ touch_nmi_watchdog(); ++ } ++ } while (any_progress); ++ ++ printk_cpu_sync_put_irqrestore(flags); ++} ++#else /* CONFIG_HAVE_ATOMIC_CONSOLE && CONFIG_PRINTK */ ++#define atomic_console_flush_all() ++#endif ++ + /** + * console_unlock - unlock the console system + * +@@ -3164,6 +3385,11 @@ void console_unblank(void) + */ + void console_flush_on_panic(enum con_flush_mode mode) + { ++ if (mode == CONSOLE_ATOMIC_FLUSH_PENDING) { ++ atomic_console_flush_all(); ++ return; ++ } ++ + /* + * If someone else is holding the console lock, trylock will fail + * and may_schedule may be set. Ignore and proceed to unlock so +@@ -3180,7 +3406,7 @@ void console_flush_on_panic(enum con_flush_mode mode) + + seq = prb_first_valid_seq(prb); + for_each_console(c) +- c->seq = seq; ++ write_console_seq(c, seq, false); + } + console_unlock(); + } +@@ -3420,19 +3646,22 @@ void register_console(struct console *newcon) + console_drivers->next = newcon; + } + +- newcon->dropped = 0; ++ atomic_long_set(&newcon->dropped, 0); + newcon->thread = NULL; + newcon->blocked = true; + mutex_init(&newcon->lock); ++#ifdef CONFIG_HAVE_ATOMIC_CONSOLE ++ newcon->atomic_data = NULL; ++#endif + + if (newcon->flags & CON_PRINTBUFFER) { + /* Get a consistent copy of @syslog_seq. */ + mutex_lock(&syslog_lock); +- newcon->seq = syslog_seq; ++ write_console_seq(newcon, syslog_seq, false); + mutex_unlock(&syslog_lock); + } else { + /* Begin with next message. */ +- newcon->seq = prb_next_seq(prb); ++ write_console_seq(newcon, prb_next_seq(prb), false); + } + + if (printk_kthreads_available) +@@ -3515,6 +3744,10 @@ int unregister_console(struct console *console) + + console_sysfs_notify(); + ++#ifdef CONFIG_HAVE_ATOMIC_CONSOLE ++ free_atomic_data(console->atomic_data); ++#endif ++ + if (console->exit) + res = console->exit(console); + +@@ -3645,7 +3878,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre + for_each_console(c) { + if (con && con != c) + continue; +- if (!console_is_usable(c)) ++ if (!console_is_usable(c, false)) + continue; + printk_seq = c->seq; + if (printk_seq < seq) +@@ -3734,9 +3967,10 @@ static void printk_fallback_preferred_direct(void) + * 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) ++ char *dropped_text, bool atomic_printing) + { +- return __console_emit_next_record(con, text, ext_text, dropped_text, NULL); ++ return __console_emit_next_record(con, text, ext_text, dropped_text, ++ atomic_printing, NULL); + } + + static bool printer_should_wake(struct console *con, u64 seq) +@@ -3777,6 +4011,11 @@ static int printk_kthread_func(void *data) + char *text; + int error; + ++#ifdef CONFIG_HAVE_ATOMIC_CONSOLE ++ if (con->write_atomic) ++ con->atomic_data = alloc_atomic_data(con->flags); ++#endif ++ + text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL); + if (!text) { + con_printk(KERN_ERR, con, "failed to allocate text buffer\n"); +@@ -3854,7 +4093,7 @@ static int printk_kthread_func(void *data) + * which can conditionally invoke cond_resched(). + */ + console_may_schedule = 0; +- console_emit_next_record(con, text, ext_text, dropped_text); ++ console_emit_next_record(con, text, ext_text, dropped_text, false); + + seq = con->seq; + +-- +2.43.0 + |