From:   Vernon Yang <vernon2gm@gmail.com>
To:     torvalds@linux-foundation.org, tytso@mit.edu, Jason@zx2c4.com,
        davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
        pabeni@redhat.com, jejb@linux.ibm.com, martin.petersen@oracle.com,
        yury.norov@gmail.com, andriy.shevchenko@linux.intel.com,
        linux@rasmusvillemoes.dk, james.smart@broadcom.com,
        dick.kennedy@broadcom.com
Cc:     linux-kernel@vger.kernel.org, wireguard@lists.zx2c4.com,
        netdev@vger.kernel.org, linux-scsi@vger.kernel.org,
        Vernon Yang <vernon2gm@gmail.com>
Subject: [PATCH v2 1/4] random: fix try_to_generate_entropy() if no further cpus set
Date:   Tue,  7 Mar 2023 04:47:20 +0800
Message-Id: <20230306204723.2584724-2-vernon2gm@gmail.com>
In-Reply-To: <20230306204723.2584724-1-vernon2gm@gmail.com>
References: <20230306204723.2584724-1-vernon2gm@gmail.com>
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When cpumask_next() the return value is greater than or equal to
nr_cpu_ids, it indicates invalid.

Before commit 596ff4a09b89 ("cpumask: re-introduce constant-sized cpumask
optimizations"), when cpumask_next() returned an invalid cpu, the driver
used the judgment equal to nr_cpu_ids to indicate the invalid cpu, so it
happened to work normally, but this is the wrong approach.

After commit 596ff4a09b89 ("cpumask: re-introduce constant-sized cpumask
optimizations"), these incorrect practices actively buggy, so fix it to
correctly.

Signed-off-by: Vernon Yang <vernon2gm@gmail.com>
---
 drivers/char/random.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index ce3ccd172cc8..253f2ddb8913 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1311,7 +1311,7 @@ static void __cold try_to_generate_entropy(void)
 			/* Basic CPU round-robin, which avoids the current CPU. */
 			do {
 				cpu = cpumask_next(cpu, &timer_cpus);
-				if (cpu == nr_cpumask_bits)
+				if (cpu >= nr_cpu_ids)
 					cpu = cpumask_first(&timer_cpus);
 			} while (cpu == smp_processor_id() && num_cpus > 1);
 
-- 
2.34.1