lkml.org 
[lkml]   [2003]   [Aug]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] [1/2] random: SMP locking
On Sat, Aug 02, 2003 at 04:00:15AM -0700, Andrew Morton wrote:
> Oliver Xymoron <oxymoron@waste.org> wrote:
> >
> > This patch adds locking for SMP. Apparently Willy never managed to
> > revive his laptop with his version so I revived mine.
>
> hrm. I'm a random ignoramus. I'll look it over...
>
> Are you really sure that all the decisions about where to use spin_lock()
> vs spin_lock_irq() vs spin_lock_irqsave() are correct? They are
> non-obvious.

Aside from the put_user stuff below, yes.

&batch_lock
batch_entropy_store can be called from any context, and typically from
interrupts -> spin_lock_irqsave

batch_entropy_process is called called via schedule_delayed_work and
runs in process context -> spin_lock_irq

&r->lock
the mixing process is too expensive to be called from an interrupt
context and the basic worker function extract_entropy can sleep, so
all this stuff can be under a normal spin_lock


> > @@ -1619,18 +1660,23 @@
> > if (!capable(CAP_SYS_ADMIN))
> > return -EPERM;
> > p = (int *) arg;
> > + spin_lock(&random_state->lock);
> > ent_count = random_state->entropy_count;
> > if (put_user(ent_count, p++) ||
> > get_user(size, p) ||
> > put_user(random_state->poolinfo.poolwords, p++))
>
> Cannot perform userspace access while holding a lock - a pagefault could
> occur, perform IO, schedule away and the same CPU tries to take the same
> lock via a different process.

Doh. Fixed. All the other userspace transfers are done without locks.

diff -urN -X dontdiff orig/drivers/char/random.c work/drivers/char/random.c
--- orig/drivers/char/random.c 2003-07-13 22:30:36.000000000 -0500
+++ work/drivers/char/random.c 2003-08-02 09:28:04.000000000 -0500
@@ -484,6 +484,7 @@
int extract_count;
struct poolinfo poolinfo;
__u32 *pool;
+ spinlock_t lock;
};

/*
@@ -522,6 +523,7 @@
return -ENOMEM;
}
memset(r->pool, 0, POOLBYTES);
+ r->lock = SPIN_LOCK_UNLOCKED;
*ret_bucket = r;
return 0;
}
@@ -564,6 +566,8 @@
int wordmask = r->poolinfo.poolwords - 1;
__u32 w;

+ spin_lock(&r->lock);
+
while (nwords--) {
w = rotate_left(r->input_rotate, *in++);
i = r->add_ptr = (r->add_ptr - 1) & wordmask;
@@ -587,6 +591,8 @@
w ^= r->pool[i];
r->pool[i] = (w >> 3) ^ twist_table[w & 7];
}
+
+ spin_unlock(&r->lock);
}

/*
@@ -594,6 +600,8 @@
*/
static void credit_entropy_store(struct entropy_store *r, int nbits)
{
+ spin_lock(&r->lock);
+
if (r->entropy_count + nbits < 0) {
DEBUG_ENT("negative entropy/overflow (%d+%d)\n",
r->entropy_count, nbits);
@@ -608,6 +616,8 @@
r == random_state ? "primary" : "unknown",
nbits, r->entropy_count);
}
+
+ spin_unlock(&r->lock);
}

/**********************************************************************
@@ -618,27 +628,33 @@
*
**********************************************************************/

-static __u32 *batch_entropy_pool;
-static int *batch_entropy_credit;
-static int batch_max;
+struct sample {
+ __u32 data[2];
+ int credit;
+};
+
+static struct sample *batch_entropy_pool, *batch_entropy_copy;
static int batch_head, batch_tail;
+static spinlock_t batch_lock = SPIN_LOCK_UNLOCKED;
+
+static int batch_max;
static void batch_entropy_process(void *private_);
static DECLARE_WORK(batch_work, batch_entropy_process, NULL);

/* note: the size must be a power of 2 */
static int __init batch_entropy_init(int size, struct entropy_store *r)
{
- batch_entropy_pool = kmalloc(2*size*sizeof(__u32), GFP_KERNEL);
+ batch_entropy_pool = kmalloc(size*sizeof(struct sample), GFP_KERNEL);
if (!batch_entropy_pool)
return -1;
- batch_entropy_credit =kmalloc(size*sizeof(int), GFP_KERNEL);
- if (!batch_entropy_credit) {
+ batch_entropy_copy = kmalloc(size*sizeof(struct sample), GFP_KERNEL);
+ if (!batch_entropy_copy) {
kfree(batch_entropy_pool);
return -1;
}
batch_head = batch_tail = 0;
- batch_max = size;
batch_work.data = r;
+ batch_max = size;
return 0;
}

@@ -650,27 +666,33 @@
*/
void batch_entropy_store(u32 a, u32 b, int num)
{
- int new;
+ int new;
+ unsigned long flags;

if (!batch_max)
return;
+
+ spin_lock_irqsave(&batch_lock, flags);

- batch_entropy_pool[2*batch_head] = a;
- batch_entropy_pool[(2*batch_head) + 1] = b;
- batch_entropy_credit[batch_head] = num;
+ batch_entropy_pool[batch_head].data[0] = a;
+ batch_entropy_pool[batch_head].data[1] = b;
+ batch_entropy_pool[batch_head].credit = num;

- new = (batch_head+1) & (batch_max-1);
- if ((unsigned)(new - batch_tail) >= (unsigned)(batch_max / 2)) {
+ if (((batch_head - batch_tail) & (batch_max-1)) >= (batch_max / 2)) {
/*
* Schedule it for the next timer tick:
*/
schedule_delayed_work(&batch_work, 1);
- batch_head = new;
- } else if (new == batch_tail) {
+ }
+
+ new = (batch_head+1) & (batch_max-1);
+ if (new == batch_tail) {
DEBUG_ENT("batch entropy buffer full\n");
} else {
batch_head = new;
}
+
+ spin_unlock_irqrestore(&batch_lock, flags);
}

/*
@@ -682,20 +704,34 @@
{
struct entropy_store *r = (struct entropy_store *) private_, *p;
int max_entropy = r->poolinfo.POOLBITS;
+ unsigned head, tail;

- if (!batch_max)
- return;
+ /* Mixing into the pool is expensive, so copy over the batch
+ * data and release the batch lock. The pool is at least half
+ * full, so don't worry too much about copying only the used
+ * part.
+ */
+ spin_lock_irq(&batch_lock);
+
+ memcpy(batch_entropy_copy, batch_entropy_pool,
+ batch_max*sizeof(struct sample));
+
+ head = batch_head;
+ tail = batch_tail;
+ batch_tail = batch_head;
+
+ spin_unlock_irq(&batch_lock);

p = r;
- while (batch_head != batch_tail) {
+ while (head != tail) {
if (r->entropy_count >= max_entropy) {
r = (r == sec_random_state) ? random_state :
sec_random_state;
max_entropy = r->poolinfo.POOLBITS;
}
- add_entropy_words(r, batch_entropy_pool + 2*batch_tail, 2);
- credit_entropy_store(r, batch_entropy_credit[batch_tail]);
- batch_tail = (batch_tail+1) & (batch_max-1);
+ add_entropy_words(r, batch_entropy_copy[tail].data, 2);
+ credit_entropy_store(r, batch_entropy_copy[tail].credit);
+ tail = (tail+1) & (batch_max-1);
}
if (p->entropy_count >= random_read_wakeup_thresh)
wake_up_interruptible(&random_read_wait);
@@ -1286,6 +1322,9 @@

DEBUG_ENT("%s has %d bits, want %d bits\n",
r == sec_random_state ? "secondary" :
+ /* Hold lock while accounting */
+ spin_lock(&r->lock);
+
r == random_state ? "primary" : "unknown",
r->entropy_count, nbytes * 8);

@@ -1298,6 +1337,8 @@
wake_up_interruptible(&random_write_wait);

r->extract_count += nbytes;
+
+ spin_unlock(&r->lock);

ret = 0;
while (nbytes) {
@@ -1593,7 +1634,7 @@
random_ioctl(struct inode * inode, struct file * file,
unsigned int cmd, unsigned long arg)
{
- int *p, size, ent_count;
+ int *p, *tmp, size, ent_count;
int retval;

switch (cmd) {
@@ -1619,18 +1660,40 @@
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
p = (int *) arg;
- ent_count = random_state->entropy_count;
- if (put_user(ent_count, p++) ||
- get_user(size, p) ||
+ if (get_user(size, p) ||
put_user(random_state->poolinfo.poolwords, p++))
- return -EFAULT;
+ goto fail;
if (size < 0)
- return -EINVAL;
+ goto fail;
if (size > random_state->poolinfo.poolwords)
size = random_state->poolinfo.poolwords;
- if (copy_to_user(p, random_state->pool, size * sizeof(__u32)))
- return -EFAULT;
+
+ /* prepare to atomically snapshot pool */
+
+ tmp = kmalloc(size * sizeof(__u32), GFP_KERNEL);
+
+ if (!tmp)
+ goto fail;
+
+ spin_lock(&random_state->lock);
+ ent_count = random_state->entropy_count;
+ memcpy(tmp, random_state->pool, size * sizeof(__u32));
+ spin_unlock(&random_state->lock);
+
+ if (!copy_to_user(p, tmp, size * sizeof(__u32))) {
+ kfree(tmp);
+ goto fail;
+ }
+
+ kfree(tmp);
+
+ if(put_user(ent_count, p++))
+ goto fail;
+
return 0;
+ fail:
+ spin_unlock(&random_state->lock);
+ return -EFAULT;
case RNDADDENTROPY:
if (!capable(CAP_SYS_ADMIN))
return -EPERM;

--
Matt Mackall : http://www.selenic.com : of or relating to the moon
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:47    [from the cache]
©2003-2011 Jasper Spaans