Commit e206f33e authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

srcu: Fill out polled grace-period APIs 



This commit adds the get_completed_synchronize_srcu() and the
same_state_synchronize_srcu() functions.  The first returns a cookie
that is always interpreted as corresponding to an expired grace period.
The second does an equality comparison of a pair of cookies.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
parent d7b0615c

include/linux/srcu.h

+31 −0
Original line number Diff line number Diff line
@@ -57,6 +57,20 @@ void cleanup_srcu_struct(struct srcu_struct *ssp); 
int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);

void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);

void synchronize_srcu(struct srcu_struct *ssp);



#define SRCU_GET_STATE_COMPLETED 0x1



/**

 * get_completed_synchronize_srcu - Return a pre-completed polled state cookie

 *

 * Returns a value that poll_state_synchronize_srcu() will always treat

 * as a cookie whose grace period has already completed.

 */

static inline unsigned long get_completed_synchronize_srcu(void)

{

	return SRCU_GET_STATE_COMPLETED;

}



unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);

unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);

bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
@@ -65,6 +79,23 @@ bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie); 
// not-yet-completed SRCU grace periods.

#define NUM_ACTIVE_SRCU_POLL_OLDSTATE 2



/**

 * same_state_synchronize_srcu - Are two old-state values identical?

 * @oldstate1: First old-state value.

 * @oldstate2: Second old-state value.

 *

 * The two old-state values must have been obtained from either

 * get_state_synchronize_srcu(), start_poll_synchronize_srcu(), or

 * get_completed_synchronize_srcu().  Returns @true if the two values are

 * identical and @false otherwise.  This allows structures whose lifetimes

 * are tracked by old-state values to push these values to a list header,

 * allowing those structures to be slightly smaller.

 */

static inline bool same_state_synchronize_srcu(unsigned long oldstate1, unsigned long oldstate2)

{

	return oldstate1 == oldstate2;

}



#ifdef CONFIG_NEED_SRCU_NMI_SAFE

int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);

void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);

kernel/rcu/srcutiny.c

+2 −1
Original line number Diff line number Diff line
@@ -277,7 +277,8 @@ bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) 
	unsigned long cur_s = READ_ONCE(ssp->srcu_idx);



	barrier();

	return ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3);

	return cookie == SRCU_GET_STATE_COMPLETED ||

	       ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3);

}

EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);

kernel/rcu/srcutree.c

+2 −1
Original line number Diff line number Diff line
@@ -1543,7 +1543,8 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); 
 */

bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)

{

	if (!rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, cookie))

	if (cookie != SRCU_GET_STATE_COMPLETED &&

	    !rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, cookie))

		return false;

	// Ensure that the end of the SRCU grace period happens before

	// any subsequent code that the caller might execute.