Re: [PATCH] random: Support freezable kthreads in add_hwgenerator_randomness()

From: Herbert Xu
Date: Thu Aug 22 2019 - 09:44:02 EST

On Mon, Aug 19, 2019 at 08:02:45AM -0700, Stephen Boyd wrote:
> The kthread calling this function is freezable after commit 03a3bb7ae631
> ("hwrng: core - Freeze khwrng thread during suspend") is applied.
> Unfortunately, this function uses wait_event_interruptible() but doesn't
> check for the kthread being woken up by the fake freezer signal. When a
> user suspends the system, this kthread will wake up and if it fails the
> entropy size check it will immediately go back to sleep and not go into
> the freezer. Eventually, suspend will fail because the task never froze
> and a warning message like this may appear:
> PM: suspend entry (deep)
> Filesystems sync: 0.000 seconds
> Freezing user space processes ... (elapsed 0.001 seconds) done.
> OOM killer disabled.
> Freezing remaining freezable tasks ...
> Freezing of tasks failed after 20.003 seconds (1 tasks refusing to freeze, wq_busy=0):
> hwrng R running task 0 289 2 0x00000020
> [<c08c64c4>] (__schedule) from [<c08c6a10>] (schedule+0x3c/0xc0)
> [<c08c6a10>] (schedule) from [<c05dbd8c>] (add_hwgenerator_randomness+0xb0/0x100)
> [<c05dbd8c>] (add_hwgenerator_randomness) from [<bf1803c8>] (hwrng_fillfn+0xc0/0x14c [rng_core])
> [<bf1803c8>] (hwrng_fillfn [rng_core]) from [<c015abec>] (kthread+0x134/0x148)
> [<c015abec>] (kthread) from [<c01010e8>] (ret_from_fork+0x14/0x2c)
> Check for a freezer signal here and skip adding any randomness if the
> task wakes up because it was frozen. This should make the kthread freeze
> properly and suspend work again.
> Fixes: 03a3bb7ae631 ("hwrng: core - Freeze khwrng thread during suspend")
> Reported-by: Keerthy <j-keerthy@xxxxxx>
> Tested-by: Keerthy <j-keerthy@xxxxxx>
> Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> ---
> Probably needs to go via Herbert who routed the patch this is fixing.
> drivers/char/random.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)

Patch applied. Thanks.
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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