Commit ff296293 authored Aug 19, 2019 by Stephen Boyd Committed by Herbert Xu Aug 22, 2019

random: Support freezable kthreads in add_hwgenerator_randomness()



The kthread calling this function is freezable after commit 03a3bb7a
("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: 03a3bb7a ("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>

parent 19842963

drivers/char/random.c

+7 −3

Original line number	Original line	Diff line number	Diff line
	@@ -2429,6 +2429,7 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
	size_t entropy)		size_t entropy)
	{		{
	struct entropy_store *poolp = &input_pool;		struct entropy_store *poolp = &input_pool;
			bool frozen = false;

	if (unlikely(crng_init == 0)) {		if (unlikely(crng_init == 0)) {
	crng_fast_load(buffer, count);		crng_fast_load(buffer, count);
	@@ -2439,9 +2440,12 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
	* We'll be woken up again once below random_write_wakeup_thresh,		* We'll be woken up again once below random_write_wakeup_thresh,
	* or when the calling thread is about to terminate.		* or when the calling thread is about to terminate.
	*/		*/
	wait_event_interruptible(random_write_wait, kthread_should_stop() \|\|		wait_event_interruptible(random_write_wait,
			kthread_freezable_should_stop(&frozen) \|\|
	ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);		ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);
			if (!frozen) {
	mix_pool_bytes(poolp, buffer, count);		mix_pool_bytes(poolp, buffer, count);
	credit_entropy_bits(poolp, entropy);		credit_entropy_bits(poolp, entropy);
	}		}
			}
	EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);		EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);

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