linux-kernel - [PATCH v4 2/6] hw_random: move some code out mutex

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Message-Id: <1415030186-18303-3-git-send-email-akong@redhat.com>
Date:	Mon,  3 Nov 2014 23:56:22 +0800
From:	Amos Kong <akong@...hat.com>
To:	virtualization@...ts.linux-foundation.org
Cc:	kvm@...r.kernel.org, rusty@...tcorp.com.au,
	herbert@...dor.apana.org.au, m@...s.ch, mb@...sch.de,
	mpm@...enic.com, amit.shah@...hat.com, linux-kernel@...r.kernel.org
Subject: [PATCH v4 2/6] hw_random: move some code out mutex_lock for avoiding underlying deadlock

In next patch, we use reference counting for each struct hwrng,
changing reference count also needs to take mutex_lock. Before
releasing the lock, if we try to stop a kthread that waits to
take the lock to reduce the referencing count, deadlock will
occur.

Signed-off-by: Amos Kong <akong@...hat.com>
---
 drivers/char/hw_random/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index b1b6042..a0905c8 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -474,12 +474,12 @@ void hwrng_unregister(struct hwrng *rng)
 		}
 	}
 	if (list_empty(&rng_list)) {
+		mutex_unlock(&rng_mutex);
 		unregister_miscdev();
 		if (hwrng_fill)
 			kthread_stop(hwrng_fill);
-	}
-
-	mutex_unlock(&rng_mutex);
+	} else
+		mutex_unlock(&rng_mutex);
 }
 EXPORT_SYMBOL_GPL(hwrng_unregister);
 
-- 
1.9.3

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