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authorLennart Poettering <lennart@poettering.net>2013-05-17 03:13:58 +0200
committerLennart Poettering <lennart@poettering.net>2013-05-17 04:26:27 +0200
commit45fbe937d7ca8d0da9ea276d57bc70ebd41c285e (patch)
tree95b216605530430206c7d863bca4d1d610382d25 /src/libsystemd-bus
parentd5a2b9a6f455468a0f29483303657ab4fd7013d8 (diff)
bus: add minimal locking around the memfd cache
We want to allow clients to process an sd_bus_message on a different thread than it was received on. Since unreffing a bus message might readd some of its memfds to the memfd cache add some minimal locking around the cache.
Diffstat (limited to 'src/libsystemd-bus')
-rw-r--r--src/libsystemd-bus/bus-internal.h8
-rw-r--r--src/libsystemd-bus/bus-kernel.c35
-rw-r--r--src/libsystemd-bus/sd-bus.c5
3 files changed, 41 insertions, 7 deletions
diff --git a/src/libsystemd-bus/bus-internal.h b/src/libsystemd-bus/bus-internal.h
index b6975c54a2..8f87bea781 100644
--- a/src/libsystemd-bus/bus-internal.h
+++ b/src/libsystemd-bus/bus-internal.h
@@ -24,6 +24,7 @@
#include <sys/socket.h>
#include <sys/un.h>
#include <netinet/in.h>
+#include <pthread.h>
#include "hashmap.h"
#include "prioq.h"
@@ -169,6 +170,13 @@ struct sd_bus {
void *kdbus_buffer;
+ /* We do locking around the memfd cache, since we want to
+ * allow people to process a sd_bus_message in a different
+ * thread then it was generated on and free it there. Since
+ * adding something to the memfd cache might happen when a
+ * message is released, we hence need to protect this bit with
+ * a mutex. */
+ pthread_mutex_t memfd_cache_mutex;
struct memfd_cache memfd_cache[MEMFD_CACHE_MAX];
unsigned n_memfd_cache;
diff --git a/src/libsystemd-bus/bus-kernel.c b/src/libsystemd-bus/bus-kernel.c
index ede78d7bef..699d24185e 100644
--- a/src/libsystemd-bus/bus-kernel.c
+++ b/src/libsystemd-bus/bus-kernel.c
@@ -721,6 +721,7 @@ int bus_kernel_create(const char *name, char **s) {
int bus_kernel_pop_memfd(sd_bus *bus, void **address, size_t *size) {
struct memfd_cache *c;
+ int fd;
assert(address);
assert(size);
@@ -728,8 +729,12 @@ int bus_kernel_pop_memfd(sd_bus *bus, void **address, size_t *size) {
if (!bus || !bus->is_kernel)
return -ENOTSUP;
+ assert_se(pthread_mutex_lock(&bus->memfd_cache_mutex) == 0);
+
if (bus->n_memfd_cache <= 0) {
- int fd, r;
+ int r;
+
+ assert_se(pthread_mutex_unlock(&bus->memfd_cache_mutex) == 0);
r = ioctl(bus->input_fd, KDBUS_CMD_MEMFD_NEW, &fd);
if (r < 0)
@@ -747,8 +752,18 @@ int bus_kernel_pop_memfd(sd_bus *bus, void **address, size_t *size) {
*address = c->address;
*size = c->size;
+ fd = c->fd;
+
+ assert_se(pthread_mutex_unlock(&bus->memfd_cache_mutex) == 0);
- return c->fd;
+ return fd;
+}
+
+static void close_and_munmap(int fd, void *address, size_t size) {
+ if (size > 0)
+ assert_se(munmap(address, PAGE_ALIGN(size)) == 0);
+
+ close_nointr_nofail(fd);
}
void bus_kernel_push_memfd(sd_bus *bus, int fd, void *address, size_t size) {
@@ -757,13 +772,17 @@ void bus_kernel_push_memfd(sd_bus *bus, int fd, void *address, size_t size) {
assert(fd >= 0);
assert(size == 0 || address);
- if (!bus || !bus->is_kernel ||
- bus->n_memfd_cache >= ELEMENTSOF(bus->memfd_cache)) {
+ if (!bus || !bus->is_kernel) {
+ close_and_munmap(fd, address, size);
+ return;
+ }
+
+ assert_se(pthread_mutex_lock(&bus->memfd_cache_mutex) == 0);
- if (size > 0)
- assert_se(munmap(address, PAGE_ALIGN(size)) == 0);
+ if (bus->n_memfd_cache >= ELEMENTSOF(bus->memfd_cache)) {
+ assert_se(pthread_mutex_unlock(&bus->memfd_cache_mutex) == 0);
- close_nointr_nofail(fd);
+ close_and_munmap(fd, address, size);
return;
}
@@ -780,6 +799,8 @@ void bus_kernel_push_memfd(sd_bus *bus, int fd, void *address, size_t size) {
c->size = MEMFD_CACHE_ITEM_SIZE_MAX;
} else
c->size = size;
+
+ assert_se(pthread_mutex_unlock(&bus->memfd_cache_mutex) == 0);
}
void bus_kernel_flush_memfd(sd_bus *b) {
diff --git a/src/libsystemd-bus/sd-bus.c b/src/libsystemd-bus/sd-bus.c
index fd19ff32b0..5e66a31162 100644
--- a/src/libsystemd-bus/sd-bus.c
+++ b/src/libsystemd-bus/sd-bus.c
@@ -27,6 +27,7 @@
#include <sys/poll.h>
#include <byteswap.h>
#include <sys/mman.h>
+#include <pthread.h>
#include "util.h"
#include "macro.h"
@@ -106,6 +107,8 @@ static void bus_free(sd_bus *b) {
bus_kernel_flush_memfd(b);
+ assert_se(pthread_mutex_destroy(&b->memfd_cache_mutex) == 0);
+
free(b);
}
@@ -125,6 +128,8 @@ int sd_bus_new(sd_bus **ret) {
r->negotiate_fds = true;
r->original_pid = getpid();
+ assert_se(pthread_mutex_init(&r->memfd_cache_mutex, NULL) == 0);
+
/* We guarantee that wqueue always has space for at least one
* entry */
r->wqueue = new(sd_bus_message*, 1);