244 lines
8.3 KiB
Diff
244 lines
8.3 KiB
Diff
From 92634b7c6a41eefbd7252c57b7a29a70bd236bb4 Mon Sep 17 00:00:00 2001
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Mon, 11 Sep 2023 15:21:57 +0000
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Subject: [PATCH 142/196] printk: nbcon: Implement emergency sections
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In emergency situations (something has gone wrong but the
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system continues to operate), usually important information
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(such as a backtrace) is generated via printk(). Each
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individual printk record has little meaning. It is the
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collection of printk messages that is most often needed by
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developers and users.
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In order to help ensure that the collection of printk messages
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in an emergency situation are all stored to the ringbuffer as
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quickly as possible, disable console output for that CPU while
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it is in the emergency situation. When exiting the emergency
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situation, trigger the consoles to be flushed.
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Add per-CPU emergency nesting tracking because an emergency
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can arise while in an emergency situation.
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Add functions to mark the beginning and end of emergency
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sections where the urgent messages are generated.
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Do not print if the current CPU is in an emergency state.
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Trigger console flushing when exiting all emergency nesting.
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Note that the emergency state is not system-wide. While one CPU
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is in an emergency state, another CPU may continue to print
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console messages.
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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 | 4 ++
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include/linux/printk.h | 7 +++-
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kernel/printk/nbcon.c | 81 +++++++++++++++++++++++++++++++++++++++++
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kernel/printk/printk.c | 25 ++++++++++---
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4 files changed, 109 insertions(+), 8 deletions(-)
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diff --git a/include/linux/console.h b/include/linux/console.h
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index 73515c324347..2583f13c25ba 100644
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--- a/include/linux/console.h
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+++ b/include/linux/console.h
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@@ -458,10 +458,14 @@ static inline bool console_is_registered(const struct console *con)
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hlist_for_each_entry(con, &console_list, node)
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#ifdef CONFIG_PRINTK
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+extern void nbcon_cpu_emergency_enter(void);
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+extern void nbcon_cpu_emergency_exit(void);
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extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt);
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extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt);
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extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt);
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#else
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+static inline void nbcon_cpu_emergency_enter(void) { }
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+static inline void nbcon_cpu_emergency_exit(void) { }
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static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; }
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static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; }
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static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; }
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diff --git a/include/linux/printk.h b/include/linux/printk.h
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index cf545b76131f..7a942e987b16 100644
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--- a/include/linux/printk.h
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+++ b/include/linux/printk.h
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@@ -197,6 +197,7 @@ void show_regs_print_info(const char *log_lvl);
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extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold;
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extern asmlinkage void dump_stack(void) __cold;
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void printk_trigger_flush(void);
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+void printk_legacy_allow_panic_sync(void);
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extern void nbcon_acquire(struct uart_port *up);
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extern void nbcon_release(struct uart_port *up);
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void nbcon_atomic_flush_unsafe(void);
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@@ -280,6 +281,10 @@ static inline void printk_trigger_flush(void)
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{
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}
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+static inline void printk_legacy_allow_panic_sync(void)
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+{
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+}
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+
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static inline void nbcon_acquire(struct uart_port *up)
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{
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}
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@@ -782,5 +787,3 @@ static inline void print_hex_dump_debug(const char *prefix_str, int prefix_type,
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print_hex_dump_debug(prefix_str, prefix_type, 16, 1, buf, len, true)
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#endif
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-
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-void printk_legacy_allow_panic_sync(void);
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diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
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index 1c01f88d596d..c3ee245397f6 100644
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--- a/kernel/printk/nbcon.c
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+++ b/kernel/printk/nbcon.c
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@@ -929,6 +929,29 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt)
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return nbcon_context_exit_unsafe(ctxt);
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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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+
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+/**
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+ * nbcon_get_cpu_emergency_nesting - Get the per CPU emergency nesting pointer
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+ *
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+ * Return: Either a pointer to the per CPU emergency nesting counter of
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+ * the current CPU or to the init data during early boot.
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+ */
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+static __ref unsigned int *nbcon_get_cpu_emergency_nesting(void)
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+{
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+ /*
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+ * The value of __printk_percpu_data_ready gets set in normal
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+ * context and before SMP initialization. As a result it could
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+ * never change while inside an nbcon emergency section.
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+ */
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+ if (!printk_percpu_data_ready())
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+ return &early_nbcon_pcpu_emergency_nesting;
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+
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+ return this_cpu_ptr(&nbcon_pcpu_emergency_nesting);
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+}
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+
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/**
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* nbcon_atomic_emit_one - Print one record for an nbcon console using the
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* write_atomic() callback
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@@ -971,9 +994,15 @@ static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt)
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*/
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enum nbcon_prio nbcon_get_default_prio(void)
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{
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+ unsigned int *cpu_emergency_nesting;
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+
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if (this_cpu_in_panic())
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return NBCON_PRIO_PANIC;
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+ cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
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+ if (*cpu_emergency_nesting)
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+ return NBCON_PRIO_EMERGENCY;
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+
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return NBCON_PRIO_NORMAL;
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}
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@@ -1110,6 +1139,58 @@ void nbcon_atomic_flush_unsafe(void)
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__nbcon_atomic_flush_all(prb_next_reserve_seq(prb), true);
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}
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+/**
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+ * nbcon_cpu_emergency_enter - Enter an emergency section where printk()
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+ * messages for that CPU are only stored
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+ *
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+ * Upon exiting the emergency section, all stored messages are flushed.
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+ *
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+ * Context: Any context. Disables preemption.
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+ *
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+ * When within an emergency section, no printing occurs on that CPU. This
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+ * is to allow all emergency messages to be dumped into the ringbuffer before
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+ * flushing the ringbuffer. The actual printing occurs when exiting the
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+ * outermost emergency section.
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+ */
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+void nbcon_cpu_emergency_enter(void)
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+{
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+ unsigned int *cpu_emergency_nesting;
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+
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+ preempt_disable();
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+
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+ cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
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+ (*cpu_emergency_nesting)++;
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+}
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+
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+/**
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+ * nbcon_cpu_emergency_exit - Exit an emergency section and flush the
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+ * stored messages
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+ *
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+ * Flushing only occurs when exiting all nesting for the CPU.
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+ *
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+ * Context: Any context. Enables preemption.
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+ */
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+void nbcon_cpu_emergency_exit(void)
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+{
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+ unsigned int *cpu_emergency_nesting;
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+ bool do_trigger_flush = false;
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+
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+ cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
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+
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+ WARN_ON_ONCE(*cpu_emergency_nesting == 0);
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+
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+ if (*cpu_emergency_nesting == 1)
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+ do_trigger_flush = true;
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+
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+ /* Undo the nesting count of nbcon_cpu_emergency_enter(). */
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+ (*cpu_emergency_nesting)--;
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+
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+ preempt_enable();
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+
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+ if (do_trigger_flush)
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+ printk_trigger_flush();
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+}
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+
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/**
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* nbcon_alloc - Allocate buffers needed by the nbcon console
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* @con: Console to allocate buffers for
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diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
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index 9c2e26ce16f9..11f26ad708d5 100644
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--- a/kernel/printk/printk.c
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+++ b/kernel/printk/printk.c
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@@ -2405,16 +2405,29 @@ asmlinkage int vprintk_emit(int facility, int level,
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* printing of all remaining records to all consoles so that
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* this context can return as soon as possible. Hopefully
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* another printk() caller will take over the printing.
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+ *
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+ * Also, nbcon_get_default_prio() requires migration disabled.
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*/
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preempt_disable();
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+
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/*
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- * Try to acquire and then immediately release the console
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- * semaphore. The release will print out buffers. With the
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- * spinning variant, this context tries to take over the
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- * printing from another printing context.
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+ * Do not emit for EMERGENCY priority. The console will be
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+ * explicitly flushed when exiting the emergency section.
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*/
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- if (console_trylock_spinning())
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- console_unlock();
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+ if (nbcon_get_default_prio() == NBCON_PRIO_EMERGENCY) {
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+ do_trylock_unlock = false;
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+ } else {
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+ /*
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+ * Try to acquire and then immediately release the
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+ * console semaphore. The release will print out
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+ * buffers. With the spinning variant, this context
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+ * tries to take over the printing from another
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+ * printing context.
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+ */
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+ if (console_trylock_spinning())
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+ console_unlock();
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+ }
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+
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preempt_enable();
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}
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--
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2.43.2
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