Messages in this thread Patch in this message | | | From | "Maciej S. Szmigiero" <> | Subject | [PATCH] random: Don't freeze in add_hwgenerator_randomness() if stopping kthread | Date | Sun, 10 Nov 2019 14:55:42 +0100 |
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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@maciej.szmigiero.name> --- 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);
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