linux-kernel - [PATCH v2 rcu 1/3] rcu: Delete unused rcu_gp_might_be

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Message-Id: <20241016161931.478592-1-paulmck@kernel.org>
Date: Wed, 16 Oct 2024 09:19:29 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: frederic@...nel.org,
	rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>
Subject: [PATCH v2 rcu 1/3] rcu: Delete unused rcu_gp_might_be_stalled() function

The rcu_gp_might_be_stalled() function is no longer used, so this commit
removes it.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 include/linux/rcutiny.h |  1 -
 include/linux/rcutree.h |  1 -
 kernel/rcu/tree_stall.h | 30 ------------------------------
 3 files changed, 32 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 0ee270b3f5ed2..fe42315f667fc 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -165,7 +165,6 @@ static inline bool rcu_inkernel_boot_has_ended(void) { return true; }
 static inline bool rcu_is_watching(void) { return true; }
 static inline void rcu_momentary_eqs(void) { }
 static inline void kfree_rcu_scheduler_running(void) { }
-static inline bool rcu_gp_might_be_stalled(void) { return false; }
 
 /* Avoid RCU read-side critical sections leaking across. */
 static inline void rcu_all_qs(void) { barrier(); }
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 90a684f94776e..27d86d9127817 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -40,7 +40,6 @@ void kvfree_rcu_barrier(void);
 void rcu_barrier(void);
 void rcu_momentary_eqs(void);
 void kfree_rcu_scheduler_running(void);
-bool rcu_gp_might_be_stalled(void);
 
 struct rcu_gp_oldstate {
 	unsigned long rgos_norm;
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 4432db6d0b99b..d7cdd535e50b1 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -76,36 +76,6 @@ int rcu_jiffies_till_stall_check(void)
 }
 EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);
 
-/**
- * rcu_gp_might_be_stalled - Is it likely that the grace period is stalled?
- *
- * Returns @true if the current grace period is sufficiently old that
- * it is reasonable to assume that it might be stalled.  This can be
- * useful when deciding whether to allocate memory to enable RCU-mediated
- * freeing on the one hand or just invoking synchronize_rcu() on the other.
- * The latter is preferable when the grace period is stalled.
- *
- * Note that sampling of the .gp_start and .gp_seq fields must be done
- * carefully to avoid false positives at the beginnings and ends of
- * grace periods.
- */
-bool rcu_gp_might_be_stalled(void)
-{
-	unsigned long d = rcu_jiffies_till_stall_check() / RCU_STALL_MIGHT_DIV;
-	unsigned long j = jiffies;
-
-	if (d < RCU_STALL_MIGHT_MIN)
-		d = RCU_STALL_MIGHT_MIN;
-	smp_mb(); // jiffies before .gp_seq to avoid false positives.
-	if (!rcu_gp_in_progress())
-		return false;
-	// Long delays at this point avoids false positive, but a delay
-	// of ULONG_MAX/4 jiffies voids your no-false-positive warranty.
-	smp_mb(); // .gp_seq before second .gp_start
-	// And ditto here.
-	return !time_before(j, READ_ONCE(rcu_state.gp_start) + d);
-}
-
 /* Don't do RCU CPU stall warnings during long sysrq printouts. */
 void rcu_sysrq_start(void)
 {
-- 
2.40.1