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rcu: Pull out wait_event*() condition into helper function
The condition for the wait_event_interruptible_timeout() that waits to do the next force-quiescent-state scan is a bit ornate: ((gf = READ_ONCE(rsp->gp_flags)) & RCU_GP_FLAG_FQS) || (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)) This commit therefore pulls this condition out into a helper function and comments its component conditions. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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1 changed files with 21 additions and 5 deletions
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@ -1903,6 +1903,26 @@ static int rcu_gp_init(struct rcu_state *rsp)
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return 1;
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}
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/*
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* Helper function for wait_event_interruptible_timeout() wakeup
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* at force-quiescent-state time.
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*/
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static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
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{
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struct rcu_node *rnp = rcu_get_root(rsp);
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/* Someone like call_rcu() requested a force-quiescent-state scan. */
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*gfp = READ_ONCE(rsp->gp_flags);
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if (*gfp & RCU_GP_FLAG_FQS)
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return true;
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/* The current grace period has completed. */
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if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
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return true;
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return false;
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}
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/*
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* Do one round of quiescent-state forcing.
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*/
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@ -2067,11 +2087,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
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TPS("fqswait"));
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rsp->gp_state = RCU_GP_WAIT_FQS;
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ret = wait_event_interruptible_timeout(rsp->gp_wq,
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((gf = READ_ONCE(rsp->gp_flags)) &
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RCU_GP_FLAG_FQS) ||
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(!READ_ONCE(rnp->qsmask) &&
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!rcu_preempt_blocked_readers_cgp(rnp)),
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j);
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rcu_gp_fqs_check_wake(rsp, &gf), j);
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rsp->gp_state = RCU_GP_DONE_FQS;
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/* Locking provides needed memory barriers. */
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/* If grace period done, leave loop. */
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