From: Rusty Russell <rusty@rustcorp.com.au>
Date: Mon, 8 Dec 2014 08:50:37 +0000 (+0800)
Subject: hwrng: use reference counts on each struct hwrng.
X-Git-Tag: fixes-v4.0-rc1~106^2~60
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3a2c0ba5ad00c018c0bef39a2224aca950aa33f2;p=pandora-kernel.git

hwrng: use reference counts on each struct hwrng.

current_rng holds one reference, and we bump it every time we want
to do a read from it.

This means we only hold the rng_mutex to grab or drop a reference,
so accessing /sys/devices/virtual/misc/hw_random/rng_current doesn't
block on read of /dev/hwrng.

Using a kref is overkill (we're always under the rng_mutex), but
a standard pattern.

This also solves the problem that the hwrng_fillfn thread was
accessing current_rng without a lock, which could change (eg. to NULL)
underneath it.

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>
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