tree e4de7392c51fd80f41d7c0316efc13da08ac3325
parent 198429631a85622da1d08d360ef02cfb84c95919
author Stephen Boyd <swboyd@chromium.org> 1566226965 -0700
committer Herbert Xu <herbert@gondor.apana.org.au> 1566448776 +1000

random: Support freezable kthreads in add_hwgenerator_randomness()

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@ti.com>
Tested-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>