linux-kernel - Re: [PATCH] random: Support freezable kthreads in add_hwgenerator

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Date:   Thu, 22 Aug 2019 15:55:19 +1000
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        linux-crypto@...r.kernel.org, Matt Mackall <mpm@...enic.com>,
        Keerthy <j-keerthy@...com>
Subject: Re: [PATCH] random: Support freezable kthreads in
 add_hwgenerator_randomness()

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@...com>
> Tested-by: Keerthy <j-keerthy@...com>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---
> 
> 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@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt