netdev - [PATCH v2 1/4] random: fix try_to_generate

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Date:   Tue,  7 Mar 2023 04:47:20 +0800
From:   Vernon Yang <vernon2gm@...il.com>
To:     torvalds@...ux-foundation.org, tytso@....edu, Jason@...c4.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, jejb@...ux.ibm.com, martin.petersen@...cle.com,
        yury.norov@...il.com, andriy.shevchenko@...ux.intel.com,
        linux@...musvillemoes.dk, james.smart@...adcom.com,
        dick.kennedy@...adcom.com
Cc:     linux-kernel@...r.kernel.org, wireguard@...ts.zx2c4.com,
        netdev@...r.kernel.org, linux-scsi@...r.kernel.org,
        Vernon Yang <vernon2gm@...il.com>
Subject: [PATCH v2 1/4] random: fix try_to_generate_entropy() if no further cpus set

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@...il.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