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rcu: Add full-sized polling for start_poll_expedited()

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The start_poll_synchronize_rcu_expedited() API compresses the combined
expedited and normal grace-period states into a single unsigned long,
which conserves storage, but can miss grace periods in certain cases
involving overlapping normal and expedited grace periods.  Missing the
occasional grace period is usually not a problem, but there are use
cases that care about each and every grace period.

This commit therefore adds yet another member of the
full-state RCU grace-period polling API, which is the
start_poll_synchronize_rcu_expedited_full() function.  This uses up to
three times the storage (rcu_gp_oldstate structure instead of unsigned
long), but is guaranteed not to miss grace periods.

[ paulmck: Apply feedback from kernel test robot and Julia Lawall. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney
2022-08-03 12:38:51 -07:00
parent 76ea364161
commit 6c502b14ba
4 changed files with 65 additions and 10 deletions
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include/linux/rcutree.h
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@@ -48,6 +48,7 @@ struct rcu_gp_oldstate {
};
unsigned long start_poll_synchronize_rcu_expedited(void);
void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp);
void cond_synchronize_rcu_expedited(unsigned long oldstate);
unsigned long get_state_synchronize_rcu(void);
void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);