Since commit 59b569480dc8
("random: Use wait_event_freezable() in add_hwgenerator_randomness()")
there is a race in add_hwgenerator_randomness() between freezing and
stopping the calling kthread.
This commit changed wait_event_interruptible() call with
kthread_freezable_should_stop() as a condition into wait_event_freezable()
with just kthread_should_stop() as a condition to fix a warning that
kthread_freezable_should_stop() might sleep inside the wait.
wait_event_freezable() ultimately calls __refrigerator() with its
check_kthr_stop argument set to false, which causes it to keep the kthread
frozen even if somebody calls kthread_stop() on it.
Calling wait_event_freezable() with kthread_should_stop() as a condition
is racy because it doesn't take into account the situation where this
condition becomes true on a kthread marked for freezing only after this
condition has already been checked.
Calling freezing() should avoid the issue that the commit 59b569480dc8 has
fixed, as it is only a checking function, it doesn't actually do the
freezing.
add_hwgenerator_randomness() has two post-boot users: in khwrng the
kthread will be frozen anyway by call to kthread_freezable_should_stop()
in its main loop, while its second user (ath9k-hwrng) is not freezable at
all.
This change allows a VM with virtio-rng loaded to write s2disk image
successfully.
Fixes: 59b569480dc8 ("random: Use wait_event_freezable() in add_hwgenerator_randomness()")
Signed-off-by: Maciej S. Szmigiero <mail@xxxxxxxxxxxxxxxxxxxxx>
---
drivers/char/random.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index de434feb873a..2f87910dd498 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2500,8 +2500,8 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
* We'll be woken up again once below random_write_wakeup_thresh,
* or when the calling thread is about to terminate.
*/
- wait_event_freezable(random_write_wait,
- kthread_should_stop() ||
+ wait_event_interruptible(random_write_wait,
+ kthread_should_stop() || freezing(current) ||
ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);
mix_pool_bytes(poolp, buffer, count);
credit_entropy_bits(poolp, entropy);
