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

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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: John Ogness <john.ogness@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230916192007.608398-9-john.ogness@linutronix.de
This commit is contained in:
Thomas Gleixner 2023-09-16 21:26:07 +02:06 committed by Petr Mladek
parent 06653d57ff
commit 9757acd0a7
2 changed files with 85 additions and 0 deletions
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10
include/linux/console.h
View File

@ -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;

75
kernel/printk/nbcon.c
View File

@ -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