[PATCH v3 1/3] spinlock: remove volatile qualifier

[Thomas Monjalon]

When compiling with C++20 standard requirement (default in GCC 16),
the increment and decrement of volatile variables are rejected:

rte_spinlock.h:241:14: error:
        '++' expression of 'volatile'-qualified type is deprecated
rte_spinlock.h:252:21: error:
        '--' expression of 'volatile'-qualified type is deprecated
rte_spinlock.h:278:14: error:
        '++' expression of 'volatile'-qualified type is deprecated

The count field of rte_spinlock_recursive_t
does not need the volatile qualifier
because it is only accessed by the thread holding the lock,
which already provides the necessary memory ordering.

The user field can be accessed outside of the lock,
so it must handled as a C11 atomic variable.
The name is also changed from user to owner.
It will break if an application is accessing this field directly,
which should never happen.

Fixes: af75078fece3 ("first public release")
Cc: sta...@dpdk.org

Signed-off-by: Thomas Monjalon <tho...@monjalon.net>
---
v1: drop volatile keyword
v2: make user an atomic variable
v3: rename user as owner
---
 lib/eal/include/generic/rte_spinlock.h | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/lib/eal/include/generic/rte_spinlock.h 
b/lib/eal/include/generic/rte_spinlock.h
index c907d4e45c..ffdcb8fa3d 100644
--- a/lib/eal/include/generic/rte_spinlock.h
+++ b/lib/eal/include/generic/rte_spinlock.h
@@ -197,8 +197,8 @@ rte_spinlock_trylock_tm(rte_spinlock_t *sl)
  */
 typedef struct {
        rte_spinlock_t sl; /**< the actual spinlock */
-       volatile int user; /**< core id using lock, -1 for unused */
-       volatile int count; /**< count of time this lock has been called */
+       RTE_ATOMIC(int) owner; /**< core id using lock, -1 for unused */
+       int count; /**< count of time this lock has been called */
 } rte_spinlock_recursive_t;
 
 /**
@@ -215,7 +215,7 @@ typedef struct {
 static inline void rte_spinlock_recursive_init(rte_spinlock_recursive_t *slr)
 {
        rte_spinlock_init(&slr->sl);
-       slr->user = -1;
+       rte_atomic_store_explicit(&slr->owner, -1, rte_memory_order_relaxed);
        slr->count = 0;
 }
 
@@ -230,9 +230,9 @@ static inline void 
rte_spinlock_recursive_lock(rte_spinlock_recursive_t *slr)
 {
        int id = rte_gettid();
 
-       if (slr->user != id) {
+       if (rte_atomic_load_explicit(&slr->owner, rte_memory_order_relaxed) != 
id) {
                rte_spinlock_lock(&slr->sl);
-               slr->user = id;
+               rte_atomic_store_explicit(&slr->owner, id, 
rte_memory_order_relaxed);
        }
        slr->count++;
 }
@@ -246,10 +246,9 @@ static inline void 
rte_spinlock_recursive_unlock(rte_spinlock_recursive_t *slr)
        __rte_no_thread_safety_analysis
 {
        if (--(slr->count) == 0) {
-               slr->user = -1;
+               rte_atomic_store_explicit(&slr->owner, -1, 
rte_memory_order_relaxed);
                rte_spinlock_unlock(&slr->sl);
        }
-
 }
 
 /**
@@ -266,10 +265,10 @@ static inline int 
rte_spinlock_recursive_trylock(rte_spinlock_recursive_t *slr)
 {
        int id = rte_gettid();
 
-       if (slr->user != id) {
+       if (rte_atomic_load_explicit(&slr->owner, rte_memory_order_relaxed) != 
id) {
                if (rte_spinlock_trylock(&slr->sl) == 0)
                        return 0;
-               slr->user = id;
+               rte_atomic_store_explicit(&slr->owner, id, 
rte_memory_order_relaxed);
        }
        slr->count++;
        return 1;
-- 
2.54.0