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hwrng: core - sleep interruptible in read 

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>
This commit is contained in:
Jiri Slaby 2015-11-27 16:50:43 +01:00 committed by Herbert Xu
parent c012a79d0c
commit 1ab87298cb
1 changed files with 5 additions and 1 deletions
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6
drivers/char/hw_random/core.c
View File

@ -238,7 +238,10 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf,
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;
}