Commit 9757acd0 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Petr Mladek
Browse files

printk: nbcon: Allow drivers to mark unsafe regions and check state 



For the write_atomic callback, the console driver may have unsafe
regions that need to be appropriately marked. Provide functions
that accept the nbcon_write_context struct to allow for the driver
to enter and exit unsafe regions.

Also provide a function for drivers to check if they are still the
owner of the console.

Co-developed-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Signed-off-by: default avatarThomas Gleixner (Intel) <tglx@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230916192007.608398-9-john.ogness@linutronix.de
parent 06653d57

include/linux/console.h

+10 −0
Original line number Diff line number Diff line
@@ -451,6 +451,16 @@ static inline bool console_is_registered(const struct console *con) 
	lockdep_assert_console_list_lock_held();			\

	hlist_for_each_entry(con, &console_list, node)



#ifdef CONFIG_PRINTK

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);

#else

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

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; }

#endif



extern int console_set_on_cmdline;

extern struct console *early_console;

kernel/printk/nbcon.c

+75 −0
Original line number Diff line number Diff line
@@ -732,6 +732,41 @@ static bool nbcon_context_can_proceed(struct nbcon_context *ctxt, struct nbcon_s 
	return false;

}



/**

 * nbcon_can_proceed - Check whether ownership can proceed

 * @wctxt:	The write context that was handed to the write function

 *

 * Return:	True if this context still owns the console. False if

 *		ownership was handed over or taken.

 *

 * It is used in nbcon_enter_unsafe() to make sure that it still owns the

 * lock. Also it is used in nbcon_exit_unsafe() to eventually free the lock

 * for a higher priority context which asked for the friendly handover.

 *

 * It can be called inside an unsafe section when the console is just

 * temporary in safe state instead of exiting and entering the unsafe state.

 *

 * Also it can be called in the safe context before doing an expensive safe

 * operation. It does not make sense to do the operation when a higher

 * priority context took the lock.

 *

 * When this function returns false then the calling context no longer owns

 * the console and is no longer allowed to go forward. In this case it must

 * back out immediately and carefully. The buffer content is also no longer

 * trusted since it no longer belongs to the calling context.

 */

bool nbcon_can_proceed(struct nbcon_write_context *wctxt)

{

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

	struct console *con = ctxt->console;

	struct nbcon_state cur;



	nbcon_state_read(con, &cur);



	return nbcon_context_can_proceed(ctxt, &cur);

}

EXPORT_SYMBOL_GPL(nbcon_can_proceed);



#define nbcon_context_enter_unsafe(c)	__nbcon_context_update_unsafe(c, true)

#define nbcon_context_exit_unsafe(c)	__nbcon_context_update_unsafe(c, false)
@@ -782,6 +817,46 @@ static bool __nbcon_context_update_unsafe(struct nbcon_context *ctxt, bool unsaf 
	return nbcon_context_can_proceed(ctxt, &cur);

}



/**

 * nbcon_enter_unsafe - Enter an unsafe region in the driver

 * @wctxt:	The write context that was handed to the write function

 *

 * Return:	True if this context still owns the console. False if

 *		ownership was handed over or taken.

 *

 * When this function returns false then the calling context no longer owns

 * the console and is no longer allowed to go forward. In this case it must

 * back out immediately and carefully. The buffer content is also no longer

 * trusted since it no longer belongs to the calling context.

 */

bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt)

{

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



	return nbcon_context_enter_unsafe(ctxt);

}

EXPORT_SYMBOL_GPL(nbcon_enter_unsafe);



/**

 * nbcon_exit_unsafe - Exit an unsafe region in the driver

 * @wctxt:	The write context that was handed to the write function

 *

 * Return:	True if this context still owns the console. False if

 *		ownership was handed over or taken.

 *

 * When this function returns false then the calling context no longer owns

 * the console and is no longer allowed to go forward. In this case it must

 * back out immediately and carefully. The buffer content is also no longer

 * trusted since it no longer belongs to the calling context.

 */

bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt)

{

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



	return nbcon_context_exit_unsafe(ctxt);

}

EXPORT_SYMBOL_GPL(nbcon_exit_unsafe);



/**

 * nbcon_emit_next_record - Emit a record in the acquired context

 * @wctxt:	The write context that will be handed to the write function