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hwrng: fix unregister race.

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The previous patch added one potential problem: we can still be
reading from a hwrng when it's unregistered.  Add a wait for zero
in the hwrng_unregister path.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Amos Kong <akong@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Rusty Russell 2014-12-08 16:50:38 +08:00 committed by Herbert Xu
parent 3a2c0ba5ad
commit a027f30d72
2 changed files with 13 additions and 0 deletions
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12
drivers/char/hw_random/core.c
View File

@ -60,6 +60,7 @@ static DEFINE_MUTEX(rng_mutex);
static DEFINE_MUTEX(reading_mutex);
static int data_avail;
static u8 *rng_buffer, *rng_fillbuf;
static DECLARE_WAIT_QUEUE_HEAD(rng_done);
static unsigned short current_quality;
static unsigned short default_quality; /* = 0; default to "off" */
@ -98,6 +99,11 @@ static inline void cleanup_rng(struct kref *kref)
if (rng->cleanup)
rng->cleanup(rng);
/* cleanup_done should be updated after cleanup finishes */
smp_wmb();
rng->cleanup_done = true;
wake_up_all(&rng_done);
}
static void set_current_rng(struct hwrng *rng)
@ -494,6 +500,8 @@ int hwrng_register(struct hwrng *rng)
add_early_randomness(rng);
}
rng->cleanup_done = false;
out_unlock:
mutex_unlock(&rng_mutex);
out:
@ -525,6 +533,10 @@ void hwrng_unregister(struct hwrng *rng)
kthread_stop(hwrng_fill);
} else
mutex_unlock(&rng_mutex);
/* Just in case rng is reading right now, wait. */
wait_event(rng_done, rng->cleanup_done &&
atomic_read(&rng->ref.refcount) == 0);
}
EXPORT_SYMBOL_GPL(hwrng_unregister);

1
include/linux/hw_random.h
View File

@ -46,6 +46,7 @@ struct hwrng {
/* internal. */
struct list_head list;
struct kref ref;
bool cleanup_done;
};
/** Register a new Hardware Random Number Generator driver. */