On Sun, Nov 10, 2019 at 02:55:42PM +0100, Maciej S. Szmigiero wrote:
> 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(-)
Patch applied. Thanks.
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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