Commit 49f7d305 authored by Marcos Paulo de Souza's avatar Marcos Paulo de Souza Committed by Petr Mladek
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printk: nbcon: Introduce KDB helpers 



These helpers will be used when calling console->write_atomic on
KDB code in the next patch. It's basically the same implementation
as nbcon_device_try_acquire, but using NBCON_PRIO_EMERGENCY when
acquiring the context.

If the acquire succeeds, the message and message length are assigned to
nbcon_write_context so ->write_atomic can print the message.

After release try to flush the console since there may be a backlog of
messages in the ringbuffer. The kthread console printers do not get a
chance to run while kdb is active.

Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Reviewed-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Signed-off-by: default avatarMarcos Paulo de Souza <mpdesouza@suse.com>
Link: https://patch.msgid.link/20251016-nbcon-kgdboc-v6-2-866aac60a80e@suse.com


Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
parent 4da42aaa

include/linux/console.h

+6 −0
Original line number Diff line number Diff line
@@ -606,6 +606,9 @@ extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt); 
extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt);

extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt);

extern void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt);

extern bool nbcon_kdb_try_acquire(struct console *con,

				  struct nbcon_write_context *wctxt);

extern void nbcon_kdb_release(struct nbcon_write_context *wctxt);



/*

 * Check if the given console is currently capable and allowed to print
@@ -655,6 +658,9 @@ static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return 
static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; }

static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; }

static inline void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) { }

static inline bool nbcon_kdb_try_acquire(struct console *con,

					 struct nbcon_write_context *wctxt) { return false; }

static inline void nbcon_kdb_release(struct console *con) { }

static inline bool console_is_usable(struct console *con, short flags,

				     bool use_atomic) { return false; }

#endif

kernel/printk/nbcon.c

+61 −0
Original line number Diff line number Diff line
@@ -1855,3 +1855,64 @@ void nbcon_device_release(struct console *con) 
	console_srcu_read_unlock(cookie);

}

EXPORT_SYMBOL_GPL(nbcon_device_release);



/**

 * nbcon_kdb_try_acquire - Try to acquire nbcon console and enter unsafe

 *			   section

 * @con:	The nbcon console to acquire

 * @wctxt:	The nbcon write context to be used on success

 *

 * Context:	Under console_srcu_read_lock() for emitting a single kdb message

 *		using the given con->write_atomic() callback. Can be called

 *		only when the console is usable at the moment.

 *

 * Return:	True if the console was acquired. False otherwise.

 *

 * kdb emits messages on consoles registered for printk() without

 * storing them into the ring buffer. It has to acquire the console

 * ownerhip so that it could call con->write_atomic() callback a safe way.

 *

 * This function acquires the nbcon console using priority NBCON_PRIO_EMERGENCY

 * and marks it unsafe for handover/takeover.

 */

bool nbcon_kdb_try_acquire(struct console *con,

			   struct nbcon_write_context *wctxt)

{

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



	memset(ctxt, 0, sizeof(*ctxt));

	ctxt->console = con;

	ctxt->prio    = NBCON_PRIO_EMERGENCY;



	if (!nbcon_context_try_acquire(ctxt, false))

		return false;



	if (!nbcon_context_enter_unsafe(ctxt))

		return false;



	return true;

}



/**

 * nbcon_kdb_release - Exit unsafe section and release the nbcon console

 *

 * @wctxt:	The nbcon write context initialized by a successful

 *		nbcon_kdb_try_acquire()

 */

void nbcon_kdb_release(struct nbcon_write_context *wctxt)

{

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



	if (!nbcon_context_exit_unsafe(ctxt))

		return;



	nbcon_context_release(ctxt);



	/*

	 * Flush any new printk() messages added when the console was blocked.

	 * Only the console used by the given write context was	blocked.

	 * The console was locked only when the write_atomic() callback

	 * was usable.

	 */

	__nbcon_atomic_flush_pending_con(ctxt->console, prb_next_reserve_seq(prb), false);

}