164 lines
4.8 KiB
Diff
164 lines
4.8 KiB
Diff
From: Thomas Gleixner <tglx@linutronix.de>
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Date: Tue, 26 Sep 2023 13:03:52 +0000
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Subject: [PATCH 124/134] printk: nbcon: Add printer thread wakeups
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
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Add a function to wakeup the printer threads. Use the new function
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when:
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- records are added to the printk ringbuffer
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- consoles are resumed
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- triggered via printk_trigger_flush()
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The actual waking is performed via irq_work so that the wakeup can
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be triggered from any context.
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Co-developed-by: John Ogness <john.ogness@linutronix.de>
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Signed-off-by: John Ogness <john.ogness@linutronix.de>
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Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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include/linux/console.h | 3 ++
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kernel/printk/internal.h | 1
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kernel/printk/nbcon.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++
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kernel/printk/printk.c | 7 +++++
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4 files changed, 67 insertions(+)
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--- a/include/linux/console.h
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+++ b/include/linux/console.h
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@@ -16,6 +16,7 @@
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#include <linux/atomic.h>
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#include <linux/bits.h>
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+#include <linux/irq_work.h>
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#include <linux/rculist.h>
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#include <linux/rcuwait.h>
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#include <linux/types.h>
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@@ -306,6 +307,7 @@ struct nbcon_write_context {
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* @locked_port: True, if the port lock is locked by nbcon
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* @kthread: Printer kthread for this console
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* @rcuwait: RCU-safe wait object for @kthread waking
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+ * @irq_work: Defer @kthread waking to IRQ work context
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*/
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struct console {
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char name[16];
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@@ -339,6 +341,7 @@ struct console {
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bool locked_port;
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struct task_struct *kthread;
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struct rcuwait rcuwait;
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+ struct irq_work irq_work;
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};
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#ifdef CONFIG_LOCKDEP
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--- a/kernel/printk/internal.h
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+++ b/kernel/printk/internal.h
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@@ -93,6 +93,7 @@ enum nbcon_prio nbcon_get_default_prio(v
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void nbcon_atomic_flush_all(void);
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bool nbcon_atomic_emit_next_record(struct console *con, bool *handover, int cookie);
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void nbcon_kthread_create(struct console *con);
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+void nbcon_wake_threads(void);
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/*
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* Check if the given console is currently capable and allowed to print
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--- a/kernel/printk/nbcon.c
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+++ b/kernel/printk/nbcon.c
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@@ -1052,6 +1052,61 @@ static int nbcon_kthread_func(void *__co
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goto wait_for_event;
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}
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+/**
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+ * nbcon_irq_work - irq work to wake printk thread
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+ * @irq_work: The irq work to operate on
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+ */
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+static void nbcon_irq_work(struct irq_work *irq_work)
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+{
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+ struct console *con = container_of(irq_work, struct console, irq_work);
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+
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+ nbcon_kthread_wake(con);
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+}
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+
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+static inline bool rcuwait_has_sleeper(struct rcuwait *w)
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+{
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+ bool has_sleeper;
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+
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+ rcu_read_lock();
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+ /*
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+ * Guarantee any new records can be seen by tasks preparing to wait
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+ * before this context checks if the rcuwait is empty.
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+ *
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+ * This full memory barrier pairs with the full memory barrier within
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+ * set_current_state() of ___rcuwait_wait_event(), which is called
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+ * after prepare_to_rcuwait() adds the waiter but before it has
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+ * checked the wait condition.
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+ *
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+ * This pairs with nbcon_kthread_func:A.
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+ */
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+ smp_mb(); /* LMM(rcuwait_has_sleeper:A) */
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+ has_sleeper = !!rcu_dereference(w->task);
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+ rcu_read_unlock();
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+
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+ return has_sleeper;
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+}
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+
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+/**
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+ * nbcon_wake_threads - Wake up printing threads using irq_work
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+ */
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+void nbcon_wake_threads(void)
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+{
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+ struct console *con;
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+ int cookie;
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+
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+ cookie = console_srcu_read_lock();
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+ for_each_console_srcu(con) {
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+ /*
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+ * Only schedule irq_work if the printing thread is
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+ * actively waiting. If not waiting, the thread will
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+ * notice by itself that it has work to do.
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+ */
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+ if (con->kthread && rcuwait_has_sleeper(&con->rcuwait))
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+ irq_work_queue(&con->irq_work);
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+ }
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+ console_srcu_read_unlock(cookie);
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+}
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+
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/* Track the nbcon emergency nesting per CPU. */
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static DEFINE_PER_CPU(unsigned int, nbcon_pcpu_emergency_nesting);
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static unsigned int early_nbcon_pcpu_emergency_nesting __initdata;
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@@ -1418,6 +1473,7 @@ void nbcon_init(struct console *con)
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BUG_ON(!con->pbufs);
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rcuwait_init(&con->rcuwait);
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+ init_irq_work(&con->irq_work, nbcon_irq_work);
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nbcon_seq_force(con, con->seq);
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nbcon_state_set(con, &state);
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}
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--- a/kernel/printk/printk.c
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+++ b/kernel/printk/printk.c
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@@ -2403,6 +2403,8 @@ asmlinkage int vprintk_emit(int facility
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}
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}
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+ nbcon_wake_threads();
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+
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if (do_trylock_unlock) {
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/*
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* The caller may be holding system-critical or
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@@ -2705,6 +2707,10 @@ void resume_console(void)
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*/
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synchronize_srcu(&console_srcu);
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+ /*
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+ * Since this runs in task context, wake the threaded printers
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+ * directly rather than scheduling irq_work to do it.
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+ */
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cookie = console_srcu_read_lock();
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for_each_console_srcu(con) {
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flags = console_srcu_read_flags(con);
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@@ -4097,6 +4103,7 @@ void defer_console_output(void)
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void printk_trigger_flush(void)
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{
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+ nbcon_wake_threads();
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defer_console_output();
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}
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