linux-kernel - [PATCH rcu 4/9] srcu: Fix the comparision in srcu_invl_snp

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Date:   Wed,  4 Jan 2023 16:28:48 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        rostedt@...dmis.org, Pingfan Liu <kernelfans@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH rcu 4/9] srcu: Fix the comparision in srcu_invl_snp_seq()

From: Pingfan Liu <kernelfans@...il.com>

A grace-period sequence number contains two fields: counter and
state.  SRCU_SNP_INIT_SEQ provides a guaranteed invalid value for
grace-period sequence numbers in newly allocated srcu_node structures'
->srcu_have_cbs[] and ->srcu_gp_seq_needed_exp fields.  The point of the
comparison in srcu_invl_snp_seq() is not to detect invalid grace-period
sequence numbers in general, but rather to detect a newly allocated
srcu_node structure whose ->srcu_have_cbs[] and ->srcu_gp_seq_needed_exp
fields need to be brought into line with the srcu_struct structure's
->srcu_gp_seq field.

This commit therefore causes srcu_invl_snp_seq() to compare both fields
of the specified grace-period sequence number.

Signed-off-by: Pingfan Liu <kernelfans@...il.com>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: <rcu@...r.kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/srcutree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 16953784a0bdf..6af0312005801 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -154,7 +154,7 @@ static void init_srcu_struct_data(struct srcu_struct *ssp)
  */
 static inline bool srcu_invl_snp_seq(unsigned long s)
 {
-	return rcu_seq_state(s) == SRCU_SNP_INIT_SEQ;
+	return s == SRCU_SNP_INIT_SEQ;
 }
 
 /*
-- 
2.31.1.189.g2e36527f23