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hashmap: make sure to initialize shared hash key atomically 

if we allocate a bunch of hash tables all at the same time, with none
earlier than the other, there's a good chance we'll initialize the
shared hash key multiple times, so that some threads will see a
different shared hash key than others.

Let's fix that, and make sure really everyone sees the same hash key.

Fixes: #17007
This commit is contained in:
Lennart Poettering 2020-09-12 00:09:07 +02:00 committed by Zbigniew Jędrzejewski-Szmek
parent 35b4e3c1bc
commit ae0b700a85
1 changed files with 7 additions and 6 deletions
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13
src/basic/hashmap.c
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@ -1,6 +1,7 @@
/* SPDX-License-Identifier: LGPL-2.1+ */
#include <errno.h>
#include <pthread.h>
#include <stdint.h>
#include <stdlib.h>
@ -19,7 +20,6 @@
#include "strv.h"
#if ENABLE_DEBUG_HASHMAP
#include <pthread.h>
#include "list.h"
#endif
@ -189,7 +189,6 @@ assert_cc(DIRECT_BUCKETS(struct set_entry) < (1 << 3));
* a handful of directly stored entries in a hashmap. When a hashmap
* outgrows direct storage, it gets its own key for indirect storage. */
static uint8_t shared_hash_key[HASH_KEY_SIZE];
static bool shared_hash_key_initialized;
/* Fields that all hashmap/set types must have */
struct HashmapBase {
@ -764,6 +763,10 @@ static void reset_direct_storage(HashmapBase *h) {
memset(p, DIB_RAW_INIT, sizeof(dib_raw_t) * hi->n_direct_buckets);
}
static void shared_hash_key_initialize(void) {
random_bytes(shared_hash_key, sizeof(shared_hash_key));
}
static struct HashmapBase* hashmap_base_new(const struct hash_ops *hash_ops, enum HashmapType type HASHMAP_DEBUG_PARAMS) {
HashmapBase *h;
const struct hashmap_type_info *hi = &hashmap_type_info[type];
@ -786,10 +789,8 @@ static struct HashmapBase* hashmap_base_new(const struct hash_ops *hash_ops, enu
reset_direct_storage(h);
if (!shared_hash_key_initialized) {
random_bytes(shared_hash_key, sizeof(shared_hash_key));
shared_hash_key_initialized= true;
}
static pthread_once_t once = PTHREAD_ONCE_INIT;
assert_se(pthread_once(&once, shared_hash_key_initialize) == 0);
#if ENABLE_DEBUG_HASHMAP
h->debug.func = func;