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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Keerthy <j-keerthy@ti.com>, Stephen Boyd <swboyd@chromium.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>
Subject: [PATCH 4.9 046/264] random: Use wait_event_freezable() in add_hwgenerator_randomness()
Date:   Thu, 23 Jun 2022 18:40:39 +0200
Message-Id: <20220623164345.372822842@linuxfoundation.org>
In-Reply-To: <20220623164344.053938039@linuxfoundation.org>
References: <20220623164344.053938039@linuxfoundation.org>
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From: Stephen Boyd <swboyd@chromium.org>

commit 59b569480dc8bb9dce57cdff133853a842dfd805 upstream.

Sebastian reports that after commit ff296293b353 ("random: Support freezable
kthreads in add_hwgenerator_randomness()") we can call might_sleep() when the
task state is TASK_INTERRUPTIBLE (state=1). This leads to the following warning.

 do not call blocking ops when !TASK_RUNNING; state=1 set at [<00000000349d1489>] prepare_to_wait_event+0x5a/0x180
 WARNING: CPU: 0 PID: 828 at kernel/sched/core.c:6741 __might_sleep+0x6f/0x80
 Modules linked in:

 CPU: 0 PID: 828 Comm: hwrng Not tainted 5.3.0-rc7-next-20190903+ #46
 RIP: 0010:__might_sleep+0x6f/0x80

 Call Trace:
  kthread_freezable_should_stop+0x1b/0x60
  add_hwgenerator_randomness+0xdd/0x130
  hwrng_fillfn+0xbf/0x120
  kthread+0x10c/0x140
  ret_from_fork+0x27/0x50

We shouldn't call kthread_freezable_should_stop() from deep within the
wait_event code because the task state is still set as
TASK_INTERRUPTIBLE instead of TASK_RUNNING and
kthread_freezable_should_stop() will try to call into the freezer with
the task in the wrong state. Use wait_event_freezable() instead so that
it calls schedule() in the right place and tries to enter the freezer
when the task state is TASK_RUNNING instead.

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Keerthy <j-keerthy@ti.com>
Fixes: ff296293b353 ("random: Support freezable kthreads in add_hwgenerator_randomness()")
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/char/random.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -327,6 +327,7 @@
 #include <linux/percpu.h>
 #include <linux/cryptohash.h>
 #include <linux/fips.h>
+#include <linux/freezer.h>
 #include <linux/ptrace.h>
 #include <linux/kmemcheck.h>
 #include <linux/workqueue.h>
@@ -2473,7 +2474,6 @@ void add_hwgenerator_randomness(const ch
 				size_t entropy)
 {
 	struct entropy_store *poolp = &input_pool;
-	bool frozen = false;
 
 	if (unlikely(crng_init == 0)) {
 		crng_fast_load(buffer, count);
@@ -2484,13 +2484,11 @@ void add_hwgenerator_randomness(const ch
 	 * We'll be woken up again once below random_write_wakeup_thresh,
 	 * or when the calling thread is about to terminate.
 	 */
-	wait_event_interruptible(random_write_wait,
-			kthread_freezable_should_stop(&frozen) ||
+	wait_event_freezable(random_write_wait,
+			kthread_should_stop() ||
 			ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);
-	if (!frozen) {
-		mix_pool_bytes(poolp, buffer, count);
-		credit_entropy_bits(poolp, entropy);
-	}
+	mix_pool_bytes(poolp, buffer, count);
+	credit_entropy_bits(poolp, entropy);
 }
 EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);