[PATCH v5] ath9k: sleep for less time when unregistering hwrng

[Jason A. Donenfeld]

Even though hwrng provides a `wait` parameter, it doesn't work very well
when waiting for a long time. There are numerous deadlocks that emerge
related to shutdown. Work around this API limitation by waiting for a
shorter amount of time and erroring more frequently. This commit also
prevents hwrng from splatting messages to dmesg when there's a timeout
and switches to using schedule_timeout_interruptible(), so that the
kthread can be stopped.

Reported-by: Gregory Erwin <gregerwin256@xxxxxxxxx>
Tested-by: Gregory Erwin <gregerwin256@xxxxxxxxx>
Cc: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Cc: Kalle Valo <kvalo@xxxxxxxxxx>
Cc: Rui Salvaterra <rsalvaterra@xxxxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: fcd09c90c3c5 ("ath9k: use hw_random API instead of directly dumping into random.c")
Link: https://lore.kernel.org/all/CAO+Okf6ZJC5-nTE_EJUGQtd8JiCkiEHytGgDsFGTEjs0c00giw@xxxxxxxxxxxxxx/
Link: https://lore.kernel.org/lkml/CAO+Okf5k+C+SE6pMVfPf-d8MfVPVq4PO7EY8Hys_DVXtent3HA@xxxxxxxxxxxxxx/
Link: https://bugs.archlinux.org/task/75138
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
---
Sorry for all the churn here in sending a v4 and v5 so soon. The
semantics of schedule_timeout_interruptible vs msleep_interruptible with
respect to kthreads is kind of confusing. I'll send a follow up patch
for that elsewhere. For now I think this should suffice for fixing the
bug.

 drivers/char/hw_random/core.c        |  3 +--
 drivers/net/wireless/ath/ath9k/rng.c | 20 +++-----------------
 2 files changed, 4 insertions(+), 19 deletions(-)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 16f227b995e8..5309fab98631 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -513,8 +513,7 @@ static int hwrng_fillfn(void *unused)
 			break;
 
 		if (rc <= 0) {
-			pr_warn("hwrng: no data available\n");
-			msleep_interruptible(10000);
+			schedule_timeout_interruptible(HZ * 10);
 			continue;
 		}
 
diff --git a/drivers/net/wireless/ath/ath9k/rng.c b/drivers/net/wireless/ath/ath9k/rng.c
index cb5414265a9b..757603d1949d 100644
--- a/drivers/net/wireless/ath/ath9k/rng.c
+++ b/drivers/net/wireless/ath/ath9k/rng.c
@@ -52,20 +52,6 @@ static int ath9k_rng_data_read(struct ath_softc *sc, u32 *buf, u32 buf_size)
 	return j << 2;
 }
 
-static u32 ath9k_rng_delay_get(u32 fail_stats)
-{
-	u32 delay;
-
-	if (fail_stats < 100)
-		delay = 10;
-	else if (fail_stats < 105)
-		delay = 1000;
-	else
-		delay = 10000;
-
-	return delay;
-}
-
 static int ath9k_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
 {
 	struct ath_softc *sc = container_of(rng, struct ath_softc, rng_ops);
@@ -80,10 +66,10 @@ static int ath9k_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
 			bytes_read += max & 3UL;
 			memzero_explicit(&word, sizeof(word));
 		}
-		if (!wait || !max || likely(bytes_read) || fail_stats > 110)
+		if (!wait || !max || likely(bytes_read) || ++fail_stats >= 100 ||
+		    ((current->flags & PF_KTHREAD) && kthread_should_stop()) ||
+		    schedule_timeout_interruptible(HZ / 20))
 			break;
-
-		msleep_interruptible(ath9k_rng_delay_get(++fail_stats));
 	}
 
 	if (wait && !bytes_read && max)
-- 
2.35.1