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%3Ba=su...

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 stable@vger.kernel.org know about it.

From 1ab87298cb59b649d8d648d25dc15b36ab865f5a Mon Sep 17 00:00:00 2001

From: Jiri Slaby jslaby@suse.cz Date: Fri, 27 Nov 2015 16:50:43 +0100 Subject: hwrng: core - sleep interruptible in read

From: Jiri Slaby jslaby@suse.cz

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

Signed-off-by: Jiri Slaby jslaby@suse.cz Cc: Matt Mackall mpm@selenic.com Cc: Herbert Xu herbert@gondor.apana.org.au Cc: linux-crypto@vger.kernel.org Signed-off-by: Herbert Xu herbert@gondor.apana.org.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

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

--- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -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 jslaby@suse.cz are

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