freebsd-dev/lib/libthr/thread/thr_pshared.c
Konstantin Belousov 53fd961f05 Lock pshared_lock shared around fork, to ensure that the COW snapshot
of the pshared hash in child is consistent and can be safely used.

Reported and tested by:	"Oleg V. Nauman" <oleg@opentransfer.com>
Sponsored by:	The FreeBSD Foundation
2016-03-21 06:52:35 +00:00

269 lines
6.3 KiB
C

/*-
* Copyright (c) 2015 The FreeBSD Foundation
*
* This software was developed by Konstantin Belousov
* under sponsorship from the FreeBSD Foundation.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/queue.h>
#include "namespace.h"
#include <stdlib.h>
#include "un-namespace.h"
#include "thr_private.h"
struct psh {
LIST_ENTRY(psh) link;
void *key;
void *val;
};
LIST_HEAD(pshared_hash_head, psh);
#define HASH_SIZE 128
static struct pshared_hash_head pshared_hash[HASH_SIZE];
#define PSHARED_KEY_HASH(key) (((unsigned long)(key) >> 8) % HASH_SIZE)
/* XXXKIB: lock could be split to per-hash chain, if appears contested */
static struct urwlock pshared_lock = DEFAULT_URWLOCK;
void
__thr_pshared_init(void)
{
int i;
_thr_urwlock_init(&pshared_lock);
for (i = 0; i < HASH_SIZE; i++)
LIST_INIT(&pshared_hash[i]);
}
static void
pshared_rlock(struct pthread *curthread)
{
curthread->locklevel++;
_thr_rwl_rdlock(&pshared_lock);
}
static void
pshared_wlock(struct pthread *curthread)
{
curthread->locklevel++;
_thr_rwl_wrlock(&pshared_lock);
}
static void
pshared_unlock(struct pthread *curthread)
{
_thr_rwl_unlock(&pshared_lock);
curthread->locklevel--;
_thr_ast(curthread);
}
/*
* Among all processes sharing a lock only one executes
* pthread_lock_destroy(). Other processes still have the hash and
* mapped off-page.
*
* Mitigate the problem by checking the liveness of all hashed keys
* periodically. Right now this is executed on each
* pthread_lock_destroy(), but may be done less often if found to be
* too time-consuming.
*/
static void
pshared_gc(struct pthread *curthread)
{
struct pshared_hash_head *hd;
struct psh *h, *h1;
int error, i;
pshared_wlock(curthread);
for (i = 0; i < HASH_SIZE; i++) {
hd = &pshared_hash[i];
LIST_FOREACH_SAFE(h, hd, link, h1) {
error = _umtx_op(NULL, UMTX_OP_SHM, UMTX_SHM_ALIVE,
h->val, NULL);
if (error == 0)
continue;
LIST_REMOVE(h, link);
munmap(h->val, PAGE_SIZE);
free(h);
}
}
pshared_unlock(curthread);
}
static void *
pshared_lookup(void *key)
{
struct pshared_hash_head *hd;
struct psh *h;
hd = &pshared_hash[PSHARED_KEY_HASH(key)];
LIST_FOREACH(h, hd, link) {
if (h->key == key)
return (h->val);
}
return (NULL);
}
static int
pshared_insert(void *key, void **val)
{
struct pshared_hash_head *hd;
struct psh *h;
hd = &pshared_hash[PSHARED_KEY_HASH(key)];
LIST_FOREACH(h, hd, link) {
/*
* When the key already exists in the hash, we should
* return either the new (just mapped) or old (hashed)
* val, and the other val should be unmapped to avoid
* address space leak.
*
* If two threads perform lock of the same object
* which is not yet stored in the pshared_hash, then
* the val already inserted by the first thread should
* be returned, and the second val freed (order is by
* the pshared_lock()). Otherwise, if we unmap the
* value obtained from the hash, the first thread
* might operate on an unmapped off-page object.
*
* There is still an issue: if hashed key was unmapped
* and then other page is mapped at the same key
* address, the hash would return the old val. I
* decided to handle the race of simultaneous hash
* insertion, leaving the unlikely remap problem
* unaddressed.
*/
if (h->key == key) {
if (h->val != *val) {
munmap(*val, PAGE_SIZE);
*val = h->val;
}
return (1);
}
}
h = malloc(sizeof(*h));
if (h == NULL)
return (0);
h->key = key;
h->val = *val;
LIST_INSERT_HEAD(hd, h, link);
return (1);
}
static void *
pshared_remove(void *key)
{
struct pshared_hash_head *hd;
struct psh *h;
void *val;
hd = &pshared_hash[PSHARED_KEY_HASH(key)];
LIST_FOREACH(h, hd, link) {
if (h->key == key) {
LIST_REMOVE(h, link);
val = h->val;
free(h);
return (val);
}
}
return (NULL);
}
static void
pshared_clean(void *key, void *val)
{
if (val != NULL)
munmap(val, PAGE_SIZE);
_umtx_op(NULL, UMTX_OP_SHM, UMTX_SHM_DESTROY, key, NULL);
}
void *
__thr_pshared_offpage(void *key, int doalloc)
{
struct pthread *curthread;
void *res;
int fd, ins_done;
curthread = _get_curthread();
pshared_rlock(curthread);
res = pshared_lookup(key);
pshared_unlock(curthread);
if (res != NULL)
return (res);
fd = _umtx_op(NULL, UMTX_OP_SHM, doalloc ? UMTX_SHM_CREAT :
UMTX_SHM_LOOKUP, key, NULL);
if (fd == -1)
return (NULL);
res = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
close(fd);
if (res == MAP_FAILED)
return (NULL);
pshared_wlock(curthread);
ins_done = pshared_insert(key, &res);
pshared_unlock(curthread);
if (!ins_done) {
pshared_clean(key, res);
res = NULL;
}
return (res);
}
void
__thr_pshared_destroy(void *key)
{
struct pthread *curthread;
void *val;
curthread = _get_curthread();
pshared_wlock(curthread);
val = pshared_remove(key);
pshared_unlock(curthread);
pshared_clean(key, val);
pshared_gc(curthread);
}
void
__thr_pshared_atfork_pre(void)
{
_thr_rwl_rdlock(&pshared_lock);
}
void
__thr_pshared_atfork_post(void)
{
_thr_rwl_unlock(&pshared_lock);
}