Commit c158834b authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

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 in
console_flush_all().

Note that the legacy printing logic uses @handover to detect
handovers for printing all consoles. For nbcon consoles,
handovers/takeovers occur on a per-console basis and thus do
not cause the console_flush_all() loop to abort.

Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240820063001.36405-23-john.ogness@linutronix.de


Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
parent 97ea9bcc

kernel/printk/internal.h

+6 −0
Original line number Diff line number Diff line
@@ -78,6 +78,8 @@ 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);
@@ -85,6 +87,8 @@ bool nbcon_alloc(struct console *con); 
void nbcon_free(struct console *con);

enum nbcon_prio nbcon_get_default_prio(void);

void nbcon_atomic_flush_pending(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
@@ -140,6 +144,8 @@ static inline bool nbcon_alloc(struct console *con) { return false; } 
static inline void nbcon_free(struct console *con) { }

static inline enum nbcon_prio nbcon_get_default_prio(void) { return NBCON_PRIO_NONE; }

static inline void nbcon_atomic_flush_pending(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; }

kernel/printk/nbcon.c

+87 −0
Original line number Diff line number Diff line
@@ -992,6 +992,93 @@ enum nbcon_prio nbcon_get_default_prio(void) 
}



/*

 * nbcon_atomic_emit_one - Print one record for an nbcon console using the

 *				write_atomic() callback

 * @wctxt:	An initialized write context struct to use for this context

 *

 * Return:	True, when a record has been printed and there are still

 *		pending records. The caller might want to continue flushing.

 *

 *		False, when there is no pending record, or when the console

 *		context cannot be acquired, or the ownership has been lost.

 *		The caller should give up. Either the job is done, cannot be

 *		done, or will be handled by the owning context.

 *

 * This is an internal helper to handle the locking of the console before

 * calling nbcon_emit_next_record().

 */

static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt)

{

	struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);



	if (!nbcon_context_try_acquire(ctxt))

		return false;



	/*

	 * nbcon_emit_next_record() returns false when the console was

	 * handed over or taken over. In both cases the context is no

	 * longer valid.

	 *

	 * The higher priority printing context takes over responsibility

	 * to print the pending records.

	 */

	if (!nbcon_emit_next_record(wctxt))

		return false;



	nbcon_context_release(ctxt);



	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 except NMI.

 * Return:	True, when a record has been printed and there are still

 *		pending records. The caller might want to continue flushing.

 *

 *		False, when there is no pending record, or when the console

 *		context cannot be acquired, or the ownership has been lost.

 *		The caller should give up. Either the job is done, cannot be

 *		done, or will be handled by the owning context.

 *

 * 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);

	unsigned long flags;

	bool progress;



	/* 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_get_default_prio();



	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_pending_con - Flush specified nbcon console using its

 *					write_atomic() callback

 * @con:			The nbcon console to flush

kernel/printk/printk.c

+12 −5
Original line number Diff line number Diff line
@@ -1860,7 +1860,7 @@ 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.
@@ -1899,7 +1899,7 @@ 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;
@@ -3021,13 +3021,20 @@ 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;



			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
@@ -3037,8 +3044,8 @@ 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;