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Release rnd_global.lock while calling an rndsource's callback. 

Obviates the need for obnoxious double-lock dances in hardware RNG
drivers.
This commit is contained in:
riastradh 2015-04-21 03:53:07 +00:00
parent 4faebe442f
commit 6be68e2895
2 changed files with 32 additions and 6 deletions
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35
sys/kern/kern_rndq.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: kern_rndq.c,v 1.67 2015/04/21 03:46:46 riastradh Exp $ */
/* $NetBSD: kern_rndq.c,v 1.68 2015/04/21 03:53:07 riastradh Exp $ */
/*-
* Copyright (c) 1997-2013 The NetBSD Foundation, Inc.
@ -32,7 +32,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_rndq.c,v 1.67 2015/04/21 03:46:46 riastradh Exp $");
__KERNEL_RCSID(0, "$NetBSD: kern_rndq.c,v 1.68 2015/04/21 03:53:07 riastradh Exp $");
#include <sys/param.h>
#include <sys/atomic.h>
@ -126,6 +126,7 @@ static struct {
kmutex_t lock;
rndpool_t pool;
LIST_HEAD(, krndsource) sources;
kcondvar_t cv;
} rnd_global __cacheline_aligned;
/*
@ -260,15 +261,32 @@ rnd_schedule_wakeup(void)
void
rnd_getmore(size_t byteswanted)
{
krndsource_t *rs;
krndsource_t *rs, *next;
mutex_spin_enter(&rnd_global.lock);
LIST_FOREACH(rs, &rnd_global.sources, list) {
LIST_FOREACH_SAFE(rs, &rnd_global.sources, list, next) {
/* Skip if there's no callback. */
if (!ISSET(rs->flags, RND_FLAG_HASCB))
continue;
KASSERT(rs->get != NULL);
KASSERT(rs->getarg != NULL);
/* Skip if there are too many users right now. */
if (rs->refcnt == UINT_MAX)
continue;
/*
* Hold a reference while we release rnd_global.lock to
* call the callback. The callback may in turn call
* rnd_add_data, which acquires rnd_global.lock.
*/
rs->refcnt++;
mutex_spin_exit(&rnd_global.lock);
rs->get(byteswanted, rs->getarg);
mutex_spin_enter(&rnd_global.lock);
if (--rs->refcnt == 0)
cv_broadcast(&rnd_global.cv);
/* Dribble some goo to the console. */
rnd_printf_verbose("rnd: entropy estimate %zu bits\n",
rndpool_get_entropy_count(&rnd_global.pool));
rnd_printf_verbose("rnd: asking source %s for %zu bytes\n",
@ -497,6 +515,7 @@ rnd_init(void)
mutex_init(&rnd_global.lock, MUTEX_DEFAULT, IPL_VM);
rndpool_init(&rnd_global.pool);
LIST_INIT(&rnd_global.sources);
cv_init(&rnd_global.cv, "rndsrc");
rnd_mempc = pool_cache_init(sizeof(rnd_sample_t), 0, 0, 0,
"rndsample", NULL, IPL_VM,
@ -652,6 +671,7 @@ rnd_attach_source(krndsource_t *rs, const char *name, uint32_t type,
rs->type = type;
rs->flags = flags;
rs->refcnt = 1;
rs->state = rnd_sample_allocate(rs);
@ -691,6 +711,11 @@ rnd_detach_source(krndsource_t *source)
mutex_spin_enter(&rnd_global.lock);
LIST_REMOVE(source, list);
if (0 < --source->refcnt) {
do {
cv_wait(&rnd_global.cv, &rnd_global.lock);
} while (0 < source->refcnt);
}
mutex_spin_exit(&rnd_global.lock);
/*

3
sys/sys/rndsource.h
View File

@ -1,4 +1,4 @@
/* $NetBSD: rndsource.h,v 1.2 2015/04/13 16:02:48 riastradh Exp $ */
/* $NetBSD: rndsource.h,v 1.3 2015/04/21 03:53:07 riastradh Exp $ */
/*-
* Copyright (c) 1997 The NetBSD Foundation, Inc.
@ -63,6 +63,7 @@ typedef struct krndsource {
void *getarg; /* argument to get-function */
void (*enable)(struct krndsource *, bool); /* turn on/off */
rngtest_t *test; /* test data for RNG type sources */
unsigned refcnt;
} krndsource_t;
static inline void