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Message-Id: <20240218185726.1994771-17-john.ogness@linutronix.de>
Date: Sun, 18 Feb 2024 20:03:16 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
linux-kernel@...r.kernel.org
Subject: [PATCH printk v2 16/26] printk: nbcon: Use nbcon consoles in console_flush_all()
Allow nbcon consoles to print messages in the legacy printk()
caller context (printing via unlock) by integrating them into
console_flush_all(). The write_atomic() callback is used for
printing.
Provide nbcon_legacy_emit_next_record(), which acts as the
nbcon variant of console_emit_next_record(). Call this variant
within console_flush_all() for nbcon consoles. Since nbcon
consoles use their own @nbcon_seq variable to track the next
record to print, this also must be appropriately handled.
Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
kernel/printk/internal.h | 6 ++++++
kernel/printk/nbcon.c | 45 ++++++++++++++++++++++++++++++++++++++++
kernel/printk/printk.c | 19 ++++++++++++-----
3 files changed, 65 insertions(+), 5 deletions(-)
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index d9a5205692fc..b34847ec6b0d 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -71,6 +71,8 @@ void defer_console_output(void);
u16 printk_parse_prefix(const char *text, int *level,
enum printk_info_flags *flags);
+void console_lock_spinning_enable(void);
+int console_lock_spinning_disable_and_check(int cookie);
u64 nbcon_seq_read(struct console *con);
void nbcon_seq_force(struct console *con, u64 seq);
@@ -78,6 +80,8 @@ bool nbcon_alloc(struct console *con);
void nbcon_init(struct console *con);
void nbcon_free(struct console *con);
void nbcon_atomic_flush_all(void);
+bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
+ int cookie);
/*
* Check if the given console is currently capable and allowed to print
@@ -133,6 +137,8 @@ static inline bool nbcon_alloc(struct console *con) { return false; }
static inline void nbcon_init(struct console *con) { }
static inline void nbcon_free(struct console *con) { }
static inline void nbcon_atomic_flush_all(void) { }
+static inline bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
+ int cookie) { return false; }
static inline bool console_is_usable(struct console *con, short flags) { return false; }
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 2eb2929c1027..747f5cbfe5ee 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -532,6 +532,7 @@ static struct printk_buffers panic_nbcon_pbufs;
* nbcon_context_try_acquire - Try to acquire nbcon console
* @ctxt: The context of the caller
*
+ * Context: Any context which could not be migrated to another CPU.
* Return: True if the console was acquired. False otherwise.
*
* If the caller allowed an unsafe hostile takeover, on success the
@@ -960,6 +961,50 @@ static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt)
return ctxt->backlog;
}
+/**
+ * nbcon_legacy_emit_next_record - Print one record for an nbcon console
+ * in legacy contexts
+ * @con: The console to print on
+ * @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
+ * both the console_lock and the SRCU read lock. Otherwise it
+ * is set to false.
+ * @cookie: The cookie from the SRCU read lock.
+ *
+ * Context: Any context which could not be migrated to another CPU.
+ * Return: True if a record could be printed, otherwise false.
+ *
+ * This function is meant to be called by console_flush_all() to print records
+ * on nbcon consoles from legacy context (printing via console unlocking).
+ * Essentially it is the nbcon version of console_emit_next_record().
+ */
+bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
+ int cookie)
+{
+ struct nbcon_write_context wctxt = { };
+ struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt);
+ bool progress = false;
+ unsigned long flags;
+
+ *handover = false;
+
+ /* Use the same procedure as console_emit_next_record(). */
+ printk_safe_enter_irqsave(flags);
+ console_lock_spinning_enable();
+ stop_critical_timings();
+
+ ctxt->console = con;
+ ctxt->prio = NBCON_PRIO_NORMAL;
+
+ progress = nbcon_atomic_emit_one(&wctxt);
+
+ start_critical_timings();
+ *handover = console_lock_spinning_disable_and_check(cookie);
+ printk_safe_exit_irqrestore(flags);
+
+ return progress;
+}
+
/**
* __nbcon_atomic_flush_all - Flush all nbcon consoles using their
* write_atomic() callback
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 1b14159990ba..d91771fb306e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1871,7 +1871,7 @@ static bool console_waiter;
* there may be a waiter spinning (like a spinlock). Also it must be
* ready to hand over the lock at the end of the section.
*/
-static void console_lock_spinning_enable(void)
+void console_lock_spinning_enable(void)
{
/*
* Do not use spinning in panic(). The panic CPU wants to keep the lock.
@@ -1910,7 +1910,7 @@ static void console_lock_spinning_enable(void)
*
* Return: 1 if the lock rights were passed, 0 otherwise.
*/
-static int console_lock_spinning_disable_and_check(int cookie)
+int console_lock_spinning_disable_and_check(int cookie)
{
int waiter;
@@ -2948,13 +2948,22 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
cookie = console_srcu_read_lock();
for_each_console_srcu(con) {
short flags = console_srcu_read_flags(con);
+ u64 printk_seq;
bool progress;
if (!console_is_usable(con, flags))
continue;
any_usable = true;
- progress = console_emit_next_record(con, handover, cookie);
+ if (flags & CON_NBCON) {
+ progress = nbcon_legacy_emit_next_record(con, handover, cookie);
+
+ printk_seq = nbcon_seq_read(con);
+ } else {
+ progress = console_emit_next_record(con, handover, cookie);
+
+ printk_seq = con->seq;
+ }
/*
* If a handover has occurred, the SRCU read lock
@@ -2964,8 +2973,8 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
return false;
/* Track the next of the highest seq flushed. */
- if (con->seq > *next_seq)
- *next_seq = con->seq;
+ if (printk_seq > *next_seq)
+ *next_seq = printk_seq;
if (!progress)
continue;
--
2.39.2
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