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rcu: Make Tiny RCU grace periods visible to polled APIs

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This commit makes the Tiny RCU implementation of synchronize_rcu()
increment the rcu_ctrlblk.gp_seq counter, thus making both
synchronize_rcu() and synchronize_rcu_expedited() visible to
get_state_synchronize_rcu() and friends.

Link: https://lore.kernel.org/all/20220121142454.1994916-1-bfoster@redhat.com/
Link: https://docs.google.com/document/d/1RNKWW9jQyfjxw2E8dsXVTdvZYh0HnYeSHDKog9jhdN8/edit?usp=sharing
Cc: Brian Foster <bfoster@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ian Kent <raven@themaw.net>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-04-14 11:49:58 -07:00
parent dd04140531
commit 7f4535366f
1 changed files with 5 additions and 2 deletions
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7
kernel/rcu/tiny.c
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@ -139,8 +139,10 @@ static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused
/*
* Wait for a grace period to elapse. But it is illegal to invoke
* synchronize_rcu() from within an RCU read-side critical section.
* Therefore, any legal call to synchronize_rcu() is a quiescent
* state, and so on a UP system, synchronize_rcu() need do nothing.
* Therefore, any legal call to synchronize_rcu() is a quiescent state,
* and so on a UP system, synchronize_rcu() need do nothing, other than
* let the polled APIs know that another grace period elapsed.
*
* (But Lai Jiangshan points out the benefits of doing might_sleep()
* to reduce latency.)
*
@ -152,6 +154,7 @@ void synchronize_rcu(void)
lock_is_held(&rcu_lock_map) ||
lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu() in RCU read-side critical section");
WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2);
}
EXPORT_SYMBOL_GPL(synchronize_rcu);