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OpenVoiceOS/buildroot-external/patches/linux/0139-printk-Avoid-console_l...

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From d0da2306d4d604ad861515b6b391bda5f4016622 Mon Sep 17 00:00:00 2001
From: John Ogness <john.ogness@linutronix.de>
Date: Tue, 26 Sep 2023 12:44:07 +0000
Subject: [PATCH 139/196] printk: Avoid console_lock dance if no legacy or boot
consoles
Currently the console lock is used to attempt legacy-type
printing even if there are no legacy or boot consoles registered.
If no such consoles are registered, the console lock does not
need to be taken.
Also, if boot consoles are registered, nbcon consoles must
perform their atomic printing under the console lock in order
to be synchronized with boot consoles.
Add tracking of legacy console registration and use it with
boot console tracking to avoid unnecessary code paths, i.e.
do not use the console lock if there are no boot consoles
and no legacy consoles.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/printk/internal.h | 12 ++++++++
kernel/printk/printk.c | 59 ++++++++++++++++++++++++++++++----------
2 files changed, 56 insertions(+), 15 deletions(-)
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index c4417fc48b7e..e2675981dfc5 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -44,6 +44,16 @@ enum printk_info_flags {
};
extern struct printk_ringbuffer *prb;
+extern bool have_legacy_console;
+extern bool have_boot_console;
+
+/*
+ * Specifies if the console lock/unlock dance is needed for console
+ * printing. If @have_boot_console is true, the nbcon consoles will
+ * be printed serially along with the legacy consoles because nbcon
+ * consoles cannot print simultaneously with boot consoles.
+ */
+#define printing_via_unlock (have_legacy_console || have_boot_console)
__printf(4, 0)
int vprintk_store(int facility, int level,
@@ -122,6 +132,8 @@ static inline bool console_is_usable(struct console *con, short flags)
#define PRINTK_MESSAGE_MAX 0
#define PRINTKRB_RECORD_MAX 0
+#define printing_via_unlock (false)
+
/*
* In !PRINTK builds we still export console_sem
* semaphore and some of console functions (console_unlock()/etc.), so
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 8a023a6db7c9..26958c8b2810 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -463,6 +463,13 @@ static int console_msg_format = MSG_FORMAT_DEFAULT;
/* syslog_lock protects syslog_* variables and write access to clear_seq. */
static DEFINE_MUTEX(syslog_lock);
+/*
+ * Specifies if a legacy console is registered. If legacy consoles are
+ * present, it is necessary to perform the console_lock/console_unlock dance
+ * whenever console flushing should occur.
+ */
+bool have_legacy_console;
+
/*
* Specifies if a boot console is registered. If boot consoles are present,
* nbcon consoles cannot print simultaneously and must be synchronized by
@@ -2345,7 +2352,7 @@ 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 && printing_via_unlock) {
/*
* The caller may be holding system-critical or
* timing-sensitive locks. Disable preemption during
@@ -2646,7 +2653,7 @@ void resume_console(void)
*/
static int console_cpu_notify(unsigned int cpu)
{
- if (!cpuhp_tasks_frozen) {
+ if (!cpuhp_tasks_frozen && printing_via_unlock) {
/* If trylock fails, someone else is doing the printing */
if (console_trylock())
console_unlock();
@@ -3189,7 +3196,8 @@ void console_flush_on_panic(enum con_flush_mode mode)
nbcon_atomic_flush_all();
- console_flush_all(false, &next_seq, &handover);
+ if (printing_via_unlock)
+ console_flush_all(false, &next_seq, &handover);
}
/*
@@ -3514,8 +3522,11 @@ void register_console(struct console *newcon)
newcon->dropped = 0;
console_init_seq(newcon, bootcon_registered);
- if (newcon->flags & CON_NBCON)
+ if (newcon->flags & CON_NBCON) {
nbcon_init(newcon);
+ } else {
+ have_legacy_console = true;
+ }
if (newcon->flags & CON_BOOT)
have_boot_console = true;
@@ -3572,6 +3583,7 @@ EXPORT_SYMBOL(register_console);
/* Must be called under console_list_lock(). */
static int unregister_console_locked(struct console *console)
{
+ bool found_legacy_con = false;
bool found_boot_con = false;
struct console *c;
int res;
@@ -3628,9 +3640,13 @@ static int unregister_console_locked(struct console *console)
for_each_console(c) {
if (c->flags & CON_BOOT)
found_boot_con = true;
+ if (!(c->flags & CON_NBCON))
+ found_legacy_con = true;
}
if (!found_boot_con)
have_boot_console = false;
+ if (!found_legacy_con)
+ have_legacy_console = false;
return res;
}
@@ -3782,6 +3798,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
u64 last_diff = 0;
u64 printk_seq;
short flags;
+ bool locked;
int cookie;
u64 diff;
u64 seq;
@@ -3791,22 +3808,28 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
seq = prb_next_reserve_seq(prb);
/* Flush the consoles so that records up to @seq are printed. */
- console_lock();
- console_unlock();
+ if (printing_via_unlock) {
+ console_lock();
+ console_unlock();
+ }
for (;;) {
unsigned long begin_jiffies;
unsigned long slept_jiffies;
+ locked = false;
diff = 0;
- /*
- * Hold the console_lock to guarantee safe access to
- * console->seq. Releasing console_lock flushes more
- * records in case @seq is still not printed on all
- * usable consoles.
- */
- console_lock();
+ if (printing_via_unlock) {
+ /*
+ * Hold the console_lock to guarantee safe access to
+ * console->seq. Releasing console_lock flushes more
+ * records in case @seq is still not printed on all
+ * usable consoles.
+ */
+ console_lock();
+ locked = true;
+ }
cookie = console_srcu_read_lock();
for_each_console_srcu(c) {
@@ -3826,6 +3849,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
if (flags & CON_NBCON) {
printk_seq = nbcon_seq_read(c);
} else {
+ WARN_ON_ONCE(!locked);
printk_seq = c->seq;
}
@@ -3837,7 +3861,8 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
if (diff != last_diff && reset_on_progress)
remaining_jiffies = timeout_jiffies;
- console_unlock();
+ if (locked)
+ console_unlock();
/* Note: @diff is 0 if there are no usable consoles. */
if (diff == 0 || remaining_jiffies == 0)
@@ -3959,7 +3984,11 @@ 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;
+
+ if (printing_via_unlock)
+ val |= PRINTK_PENDING_OUTPUT;
+ __wake_up_klogd(val);
}
void printk_trigger_flush(void)
--
2.43.2
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