On 2023-09-07 17:24, Stephen Hemminger wrote:
Add missing locking so that if two non-EAL threads call rte_rand()
they will not corrupt the per-thread state.
Fixes: 3f002f069612 ("eal: replace libc-based random generation with LFSR")
The API documentation clearly states that no MT safety guarantees are
given for unregistered non-EAL threads. So this patch doesn't fix anything.
rte_rand() is MT safe for *registered* non-EAL threads.
Signed-off-by: Stephen Hemminger <step...@networkplumber.org>
---
lib/eal/common/rte_random.c | 54 ++++++++++++++++++++++++-------------
1 file changed, 36 insertions(+), 18 deletions(-)
diff --git a/lib/eal/common/rte_random.c b/lib/eal/common/rte_random.c
index 812e5b4757b5..02b6b6b97bc0 100644
--- a/lib/eal/common/rte_random.c
+++ b/lib/eal/common/rte_random.c
@@ -11,6 +11,7 @@
#include <rte_branch_prediction.h>
#include <rte_cycles.h>
#include <rte_lcore.h>
+#include <rte_spinlock.h>
#include <rte_random.h>
struct rte_rand_state {
@@ -21,6 +22,9 @@ struct rte_rand_state {
uint64_t z5;
} __rte_cache_aligned;
+/* Used for thread safety for non EAL threads. */
+static rte_spinlock_t rte_rand_lock = RTE_SPINLOCK_INITIALIZER;
+
/* One instance each for every lcore id-equipped thread, and one
* additional instance to be shared by all others threads (i.e., all
* unregistered non-EAL threads).
@@ -124,20 +128,32 @@ struct rte_rand_state *__rte_rand_get_state(void)
idx = rte_lcore_id();
/* last instance reserved for unregistered non-EAL threads */
- if (unlikely(idx == LCORE_ID_ANY))
+ if (unlikely(idx == LCORE_ID_ANY)) {
idx = RTE_MAX_LCORE;
+ rte_spinlock_lock(&rte_rand_lock);
Non-EAL threads are very likely to be "regular" threads, which won't
have a dedicated core all for themselves, and thus may well be preempted
by the kernel. Such threads should not use spinlocks.
If a lock is to be added to achieve MT safety for parallel calls from
unregistered non-EAL threads, it should be a regular mutex.
+ }
return &rand_states[idx];
}
+static __rte_always_inline
+void __rte_rand_put_state(struct rte_rand_state *state)
+{
+ if (state == &rand_states[RTE_MAX_LCORE])
+ rte_spinlock_unlock(&rte_rand_lock);
+}
+
uint64_t
rte_rand(void)
{
struct rte_rand_state *state;
+ uint64_t res;
state = __rte_rand_get_state();
+ res = __rte_rand_lfsr258(state);
+ __rte_rand_put_state(state);
- return __rte_rand_lfsr258(state);
+ return res;
}
uint64_t
@@ -159,22 +175,24 @@ rte_rand_max(uint64_t upper_bound)
/* Handle power-of-2 upper_bound as a special case, since it
* has no bias issues.
*/
- if (unlikely(ones == 1))
- return __rte_rand_lfsr258(state) & (upper_bound - 1);
-
- /* The approach to avoiding bias is to create a mask that
- * stretches beyond the request value range, and up to the
- * next power-of-2. In case the masked generated random value
- * is equal to or greater than the upper bound, just discard
- * the value and generate a new one.
- */
-
- leading_zeros = rte_clz64(upper_bound);
- mask >>= leading_zeros;
-
- do {
- res = __rte_rand_lfsr258(state) & mask;
- } while (unlikely(res >= upper_bound));
+ if (unlikely(ones == 1)) {
+ res = __rte_rand_lfsr258(state) & (upper_bound - 1);
+ } else {
+ /* The approach to avoiding bias is to create a mask that
+ * stretches beyond the request value range, and up to the
+ * next power-of-2. In case the masked generated random value
+ * is equal to or greater than the upper bound, just discard
+ * the value and generate a new one.
+ */
+
+ leading_zeros = rte_clz64(upper_bound);
+ mask >>= leading_zeros;
+
+ do {
+ res = __rte_rand_lfsr258(state) & mask;
+ } while (unlikely(res >= upper_bound));
+ }
+ __rte_rand_put_state(state);
return res;
}
