Patch "hwrng: core - sleep interruptible in read" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

hwrng: core - sleep interruptible in read

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
hwrng-core-sleep-interruptible-in-read.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jiri Slaby <[email protected]>
Date: Fri, 27 Nov 2015 16:50:43 +0100
Subject: hwrng: core - sleep interruptible in read

From: Jiri Slaby <[email protected]>

commit 1ab87298cb59b649d8d648d25dc15b36ab865f5a upstream.

hwrng kthread can be waiting via hwrng_fillfn for some data from a rng like virtio-rng:
hwrng D ffff880093e17798 0 382 2 0x00000000
...

Call Trace:
 [<ffffffff817339c6>] wait_for_completion_killable+0x96/0x210
 [<ffffffffa00aa1b7>] virtio_read+0x57/0xf0 [virtio_rng]
 [<ffffffff814f4a35>] hwrng_fillfn+0x75/0x130
 [<ffffffff810aa243>] kthread+0xf3/0x110

And when some user program tries to read the /dev node in this state, we get:
rngd D ffff880093e17798 0 762 1 0x00000004
...

Call Trace:
 [<ffffffff817351ac>] mutex_lock_nested+0x15c/0x3e0
 [<ffffffff814f478e>] rng_dev_read+0x6e/0x240
 [<ffffffff81231958>] __vfs_read+0x28/0xe0
 [<ffffffff81232393>] vfs_read+0x83/0x130

And this is indeed unkillable. So use mutex_lock_interruptible instead of mutex_lock in rng_dev_read and exit immediatelly when interrupted. And possibly return already read data, if any (as POSIX allows).

v2: use ERESTARTSYS instead of EINTR

---
 drivers/char/hw_random/core.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

@@ -238,7 +238,10 @@ static ssize_t rng_dev_read(struct file
 			goto out;
 		}
 
-		mutex_lock(&reading_mutex);
+		if (mutex_lock_interruptible(&reading_mutex)) {
+			err = -ERESTARTSYS;
+			goto out_put;
+		}
 		if (!data_avail) {
 			bytes_read = rng_get_data(rng, rng_buffer,
 				rng_buffer_size(),

@@ -288,6 +291,7 @@ out:
 
 out_unlock_reading:
 	mutex_unlock(&reading_mutex);
+out_put:
 	put_rng(rng);
 	goto out;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/hwrng-core-sleep-interruptible-in-read.patch