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srcu: Fill out polled grace-period APIs

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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: Paul E. McKenney <paulmck@kernel.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Paul E. McKenney 2024-06-14 13:26:44 -07:00
parent d7b0615cb8
commit e206f33e2c
3 changed files with 35 additions and 2 deletions
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31
include/linux/srcu.h
View File

@ -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);

3
kernel/rcu/srcutiny.c
View File

@ -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);

3
kernel/rcu/srcutree.c
View File

@ -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.