linux-kernel - [PATCH AUTOSEL 4.9 05/21] s390/cpuinfo: fix wrong output when CPU0 is offline

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Date:   Wed, 15 Apr 2020 07:47:32 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Alexander Gordeev <agordeev@...ux.ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Sasha Levin <sashal@...nel.org>, linux-s390@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 05/21] s390/cpuinfo: fix wrong output when CPU0 is offline

From: Alexander Gordeev <agordeev@...ux.ibm.com>

[ Upstream commit 872f27103874a73783aeff2aac2b41a489f67d7c ]

/proc/cpuinfo should not print information about CPU 0 when it is offline.

Fixes: 281eaa8cb67c ("s390/cpuinfo: simplify locking and skip offline cpus early")
Signed-off-by: Alexander Gordeev <agordeev@...ux.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@...ibm.com>
[heiko.carstens@...ibm.com: shortened commit message]
Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/s390/kernel/processor.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kernel/processor.c b/arch/s390/kernel/processor.c
index d856263fd7687..737e22cf09728 100644
--- a/arch/s390/kernel/processor.c
+++ b/arch/s390/kernel/processor.c
@@ -139,8 +139,9 @@ static void show_cpu_mhz(struct seq_file *m, unsigned long n)
 static int show_cpuinfo(struct seq_file *m, void *v)
 {
 	unsigned long n = (unsigned long) v - 1;
+	unsigned long first = cpumask_first(cpu_online_mask);
 
-	if (!n)
+	if (n == first)
 		show_cpu_summary(m, v);
 	if (!machine_has_cpu_mhz)
 		return 0;
@@ -153,6 +154,8 @@ static inline void *c_update(loff_t *pos)
 {
 	if (*pos)
 		*pos = cpumask_next(*pos - 1, cpu_online_mask);
+	else
+		*pos = cpumask_first(cpu_online_mask);
 	return *pos < nr_cpu_ids ? (void *)*pos + 1 : NULL;
 }
 
-- 
2.20.1