On Wed, Jan 10, 2018 at 04:31:35PM +0000, Al Viro wrote:
> *snort*
>
> Seeing that random drivers are, by far, the majority of instances...
> What I wonder is how many of them conform to that pattern and how
> many can be massaged to that form.
>
> How painful would it be, to pick an instance with more than one wait
> queue involved, to convert drivers/char/random.c to that form?
Attached. Not very painful at all. Would be even nicer if we had a
wait_event version that can deal with keys, but I can look into that.
> static unsigned int vtpm_proxy_fops_poll(struct file *filp, poll_table *wait)
> {
> struct proxy_dev *proxy_dev = filp->private_data;
> unsigned ret;
>
> poll_wait(filp, &proxy_dev->wq, wait);
>
> ret = POLLOUT;
>
> mutex_lock(&proxy_dev->buf_lock);
>
> if (proxy_dev->req_len)
> ret |= POLLIN | POLLRDNORM;
>
> if (!(proxy_dev->state & STATE_OPENED_FLAG))
> ret |= POLLHUP;
>
> mutex_unlock(&proxy_dev->buf_lock);
>
> return ret;
> }
> (mainline drivers/char/tpm/tpm_vtpm_proxy.c)
Yeah. And what exactly is the lock protecting given that each
of them checks a single smaller than register sized variable?
> Is that mutex_lock() in there a bug? Another fun case is dma_buf_poll()...
Right now it is not a bug, but it is not very helpful behavior. We
actually have quite a few of those, and not allowing ->poll_mask to
is a good thing to catch these.
>From 5f5549dc78b39799db01d48dc346d14561ec2003 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@xxxxxx>
Date: Wed, 10 Jan 2018 18:37:51 +0100
Subject: random: convert to ->poll_mask
The big change is that random_read_wait and random_write_wait are merged
into a single waitqueue that uses keyed wakeups. Because wait_event_*
doesn't know about that this will lead to occassional spurious wakeups
in _random_read and add_hwgenerator_randomness, but wait_event_* is
designed to handle these and were are not in a a hot path there.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
drivers/char/random.c | 27 +++++++++++++++------------
1 file changed, 15 insertions(+), 12 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 64b59562c872..9a1b85928de3 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -401,8 +401,7 @@ static struct poolinfo {
/*
* Static global variables
*/
-static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
-static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
+static DECLARE_WAIT_QUEUE_HEAD(random_wait);
static struct fasync_struct *fasync;
static DEFINE_SPINLOCK(random_ready_list_lock);
@@ -710,7 +709,7 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits)
/* should we wake readers? */
if (entropy_bits >= random_read_wakeup_bits) {
- wake_up_interruptible(&random_read_wait);
+ wake_up_interruptible_poll(&random_wait, POLLIN);
kill_fasync(&fasync, SIGIO, POLL_IN);
}
/* If the input pool is getting full, send some
@@ -1293,7 +1292,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
trace_debit_entropy(r->name, 8 * ibytes);
if (ibytes &&
(r->entropy_count >> ENTROPY_SHIFT) < random_write_wakeup_bits) {
- wake_up_interruptible(&random_write_wait);
+ wake_up_interruptible_poll(&random_wait, POLLOUT);
kill_fasync(&fasync, SIGIO, POLL_OUT);
}
@@ -1748,7 +1747,7 @@ _random_read(int nonblock, char __user *buf, size_t nbytes)
if (nonblock)
return -EAGAIN;
- wait_event_interruptible(random_read_wait,
+ wait_event_interruptible(random_wait,
ENTROPY_BITS(&input_pool) >=
random_read_wakeup_bits);
if (signal_pending(current))
@@ -1784,14 +1783,17 @@ urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
return ret;
}
+static struct wait_queue_head *
+random_get_poll_head(struct file *file, __poll_t events)
+{
+ return &random_wait;
+}
+
static __poll_t
-random_poll(struct file *file, poll_table * wait)
+random_poll_mask(struct file *file, __poll_t events)
{
- __poll_t mask;
+ __poll_t mask = 0;
- poll_wait(file, &random_read_wait, wait);
- poll_wait(file, &random_write_wait, wait);
- mask = 0;
if (ENTROPY_BITS(&input_pool) >= random_read_wakeup_bits)
mask |= POLLIN | POLLRDNORM;
if (ENTROPY_BITS(&input_pool) < random_write_wakeup_bits)
@@ -1890,7 +1892,8 @@ static int random_fasync(int fd, struct file *filp, int on)
const struct file_operations random_fops = {
.read = random_read,
.write = random_write,
- .poll = random_poll,
+ .get_poll_head = random_get_poll_head,
+ .poll_mask = random_poll_mask,
.unlocked_ioctl = random_ioctl,
.fasync = random_fasync,
.llseek = noop_llseek,
@@ -2223,7 +2226,7 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
* We'll be woken up again once below random_write_wakeup_thresh,
* or when the calling thread is about to terminate.
*/
- wait_event_interruptible(random_write_wait, kthread_should_stop() ||
+ wait_event_interruptible(random_wait, kthread_should_stop() ||
ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);
mix_pool_bytes(poolp, buffer, count);
credit_entropy_bits(poolp, entropy);
--
2.14.2
