linux-kernel - [PATCH] kernel/smp: Fix an off by one in csd_lock_wait

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Date:   Thu, 9 Jul 2020 13:48:18 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kaitao Cheng <pilgrimtao@...il.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH] kernel/smp: Fix an off by one in csd_lock_wait_toolong()

The __per_cpu_offset[] array has "nr_cpu_ids" elements so change the >
>= to prevent a read one element beyond the end of the array.

Fixes: 0504bc41a62c ("kernel/smp: Provide CSD lock timeout diagnostics")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
 kernel/smp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index 78b602cae6c2..f49966713ac3 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -171,7 +171,7 @@ static __always_inline bool csd_lock_wait_toolong(call_single_data_t *csd, u64 t
 		*bug_id = atomic_inc_return(&csd_bug_count);
 	cpu = csd_lock_wait_getcpu(csd);
 	smp_mb(); // No stale cur_csd values!
-	if (WARN_ONCE(cpu < 0 || cpu > nr_cpu_ids, "%s: cpu = %d\n", __func__, cpu))
+	if (WARN_ONCE(cpu < 0 || cpu >= nr_cpu_ids, "%s: cpu = %d\n", __func__, cpu))
 		cpu_cur_csd = READ_ONCE(per_cpu(cur_csd, 0));
 	else
 		cpu_cur_csd = READ_ONCE(per_cpu(cur_csd, cpu));
-- 
2.27.0