slub: Replace cmpxchg_double()

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20230531132323.924677086@infradead.org

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index f6df03f..deb90cf 100644 (file)
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -39,7 +39,8 @@ enum stat_item {
        CPU_PARTIAL_FREE,       /* Refill cpu partial on free */
        CPU_PARTIAL_NODE,       /* Refill cpu partial from node partial */
        CPU_PARTIAL_DRAIN,      /* Drain cpu partial to node partial */
-       NR_SLUB_STAT_ITEMS };
+       NR_SLUB_STAT_ITEMS
+};
 
 #ifndef CONFIG_SLUB_TINY
 /*
@@ -47,8 +48,13 @@ enum stat_item {
  * with this_cpu_cmpxchg_double() alignment requirements.
  */
 struct kmem_cache_cpu {
-       void **freelist;        /* Pointer to next available object */
-       unsigned long tid;      /* Globally unique transaction id */
+       union {
+               struct {
+                       void **freelist;        /* Pointer to next available object */
+                       unsigned long tid;      /* Globally unique transaction id */
+               };
+               freelist_aba_t freelist_tid;
+       };
        struct slab *slab;      /* The slab from which we are allocating */
 #ifdef CONFIG_SLUB_CPU_PARTIAL
        struct slab *partial;   /* Partially allocated frozen slabs */

diff --git a/mm/slab.h b/mm/slab.h
index f01ac25..bc36edd 100644 (file)
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -6,6 +6,38 @@
  */
 void __init kmem_cache_init(void);
 
+#ifdef CONFIG_64BIT
+# ifdef system_has_cmpxchg128
+# define system_has_freelist_aba()     system_has_cmpxchg128()
+# define try_cmpxchg_freelist          try_cmpxchg128
+# endif
+#define this_cpu_try_cmpxchg_freelist  this_cpu_try_cmpxchg128
+typedef u128 freelist_full_t;
+#else /* CONFIG_64BIT */
+# ifdef system_has_cmpxchg64
+# define system_has_freelist_aba()     system_has_cmpxchg64()
+# define try_cmpxchg_freelist          try_cmpxchg64
+# endif
+#define this_cpu_try_cmpxchg_freelist  this_cpu_try_cmpxchg64
+typedef u64 freelist_full_t;
+#endif /* CONFIG_64BIT */
+
+#if defined(system_has_freelist_aba) && !defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
+#undef system_has_freelist_aba
+#endif
+
+/*
+ * Freelist pointer and counter to cmpxchg together, avoids the typical ABA
+ * problems with cmpxchg of just a pointer.
+ */
+typedef union {
+       struct {
+               void *freelist;
+               unsigned long counter;
+       };
+       freelist_full_t full;
+} freelist_aba_t;
+
 /* Reuses the bits in struct page */
 struct slab {
        unsigned long __page_flags;
@@ -38,14 +70,21 @@ struct slab {
 #endif
                        };
                        /* Double-word boundary */
-                       void *freelist;         /* first free object */
                        union {
-                               unsigned long counters;
                                struct {
-                                       unsigned inuse:16;
-                                       unsigned objects:15;
-                                       unsigned frozen:1;
+                                       void *freelist;         /* first free object */
+                                       union {
+                                               unsigned long counters;
+                                               struct {
+                                                       unsigned inuse:16;
+                                                       unsigned objects:15;
+                                                       unsigned frozen:1;
+                                               };
+                                       };
                                };
+#ifdef system_has_freelist_aba
+                               freelist_aba_t freelist_counter;
+#endif
                        };
                };
                struct rcu_head rcu_head;
@@ -72,8 +111,8 @@ SLAB_MATCH(memcg_data, memcg_data);
 #endif
 #undef SLAB_MATCH
 static_assert(sizeof(struct slab) <= sizeof(struct page));
-#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && defined(CONFIG_SLUB)
-static_assert(IS_ALIGNED(offsetof(struct slab, freelist), 2*sizeof(void *)));
+#if defined(system_has_freelist_aba) && defined(CONFIG_SLUB)
+static_assert(IS_ALIGNED(offsetof(struct slab, freelist), sizeof(freelist_aba_t)));
 #endif
 
 /**

diff --git a/mm/slub.c b/mm/slub.c
index c87628c..7529626 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -292,7 +292,12 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
 /* Poison object */
 #define __OBJECT_POISON                ((slab_flags_t __force)0x80000000U)
 /* Use cmpxchg_double */
+
+#ifdef system_has_freelist_aba
 #define __CMPXCHG_DOUBLE       ((slab_flags_t __force)0x40000000U)
+#else
+#define __CMPXCHG_DOUBLE       ((slab_flags_t __force)0U)
+#endif
 
 /*
  * Tracking user of a slab.
@@ -512,6 +517,40 @@ static __always_inline void slab_unlock(struct slab *slab)
        __bit_spin_unlock(PG_locked, &page->flags);
 }
 
+static inline bool
+__update_freelist_fast(struct slab *slab,
+                     void *freelist_old, unsigned long counters_old,
+                     void *freelist_new, unsigned long counters_new)
+{
+#ifdef system_has_freelist_aba
+       freelist_aba_t old = { .freelist = freelist_old, .counter = counters_old };
+       freelist_aba_t new = { .freelist = freelist_new, .counter = counters_new };
+
+       return try_cmpxchg_freelist(&slab->freelist_counter.full, &old.full, new.full);
+#else
+       return false;
+#endif
+}
+
+static inline bool
+__update_freelist_slow(struct slab *slab,
+                     void *freelist_old, unsigned long counters_old,
+                     void *freelist_new, unsigned long counters_new)
+{
+       bool ret = false;
+
+       slab_lock(slab);
+       if (slab->freelist == freelist_old &&
+           slab->counters == counters_old) {
+               slab->freelist = freelist_new;
+               slab->counters = counters_new;
+               ret = true;
+       }
+       slab_unlock(slab);
+
+       return ret;
+}
+
 /*
  * Interrupts must be disabled (for the fallback code to work right), typically
  * by an _irqsave() lock variant. On PREEMPT_RT the preempt_disable(), which is
@@ -519,33 +558,25 @@ static __always_inline void slab_unlock(struct slab *slab)
  * allocation/ free operation in hardirq context. Therefore nothing can
  * interrupt the operation.
  */
-static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab,
+static inline bool __slab_update_freelist(struct kmem_cache *s, struct slab *slab,
                void *freelist_old, unsigned long counters_old,
                void *freelist_new, unsigned long counters_new,
                const char *n)
 {
+       bool ret;
+
        if (USE_LOCKLESS_FAST_PATH())
                lockdep_assert_irqs_disabled();
-#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
-    defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
+
        if (s->flags & __CMPXCHG_DOUBLE) {
-               if (cmpxchg_double(&slab->freelist, &slab->counters,
-                                  freelist_old, counters_old,
-                                  freelist_new, counters_new))
-                       return true;
-       } else
-#endif
-       {
-               slab_lock(slab);
-               if (slab->freelist == freelist_old &&
-                                       slab->counters == counters_old) {
-                       slab->freelist = freelist_new;
-                       slab->counters = counters_new;
-                       slab_unlock(slab);
-                       return true;
-               }
-               slab_unlock(slab);
+               ret = __update_freelist_fast(slab, freelist_old, counters_old,
+                                           freelist_new, counters_new);
+       } else {
+               ret = __update_freelist_slow(slab, freelist_old, counters_old,
+                                           freelist_new, counters_new);
        }
+       if (likely(ret))
+               return true;
 
        cpu_relax();
        stat(s, CMPXCHG_DOUBLE_FAIL);
@@ -557,36 +588,26 @@ static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab
        return false;
 }
 
-static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab,
+static inline bool slab_update_freelist(struct kmem_cache *s, struct slab *slab,
                void *freelist_old, unsigned long counters_old,
                void *freelist_new, unsigned long counters_new,
                const char *n)
 {
-#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
-    defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
+       bool ret;
+
        if (s->flags & __CMPXCHG_DOUBLE) {
-               if (cmpxchg_double(&slab->freelist, &slab->counters,
-                                  freelist_old, counters_old,
-                                  freelist_new, counters_new))
-                       return true;
-       } else
-#endif
-       {
+               ret = __update_freelist_fast(slab, freelist_old, counters_old,
+                                           freelist_new, counters_new);
+       } else {
                unsigned long flags;
 
                local_irq_save(flags);
-               slab_lock(slab);
-               if (slab->freelist == freelist_old &&
-                                       slab->counters == counters_old) {
-                       slab->freelist = freelist_new;
-                       slab->counters = counters_new;
-                       slab_unlock(slab);
-                       local_irq_restore(flags);
-                       return true;
-               }
-               slab_unlock(slab);
+               ret = __update_freelist_slow(slab, freelist_old, counters_old,
+                                           freelist_new, counters_new);
                local_irq_restore(flags);
        }
+       if (likely(ret))
+               return true;
 
        cpu_relax();
        stat(s, CMPXCHG_DOUBLE_FAIL);
@@ -2228,7 +2249,7 @@ static inline void *acquire_slab(struct kmem_cache *s,
        VM_BUG_ON(new.frozen);
        new.frozen = 1;
 
-       if (!__cmpxchg_double_slab(s, slab,
+       if (!__slab_update_freelist(s, slab,
                        freelist, counters,
                        new.freelist, new.counters,
                        "acquire_slab"))
@@ -2554,7 +2575,7 @@ redo:
        }
 
 
-       if (!cmpxchg_double_slab(s, slab,
+       if (!slab_update_freelist(s, slab,
                                old.freelist, old.counters,
                                new.freelist, new.counters,
                                "unfreezing slab")) {
@@ -2611,7 +2632,7 @@ static void __unfreeze_partials(struct kmem_cache *s, struct slab *partial_slab)
 
                        new.frozen = 0;
 
-               } while (!__cmpxchg_double_slab(s, slab,
+               } while (!__slab_update_freelist(s, slab,
                                old.freelist, old.counters,
                                new.freelist, new.counters,
                                "unfreezing slab"));
@@ -3008,6 +3029,18 @@ static inline bool pfmemalloc_match(struct slab *slab, gfp_t gfpflags)
 }
 
 #ifndef CONFIG_SLUB_TINY
+static inline bool
+__update_cpu_freelist_fast(struct kmem_cache *s,
+                          void *freelist_old, void *freelist_new,
+                          unsigned long tid)
+{
+       freelist_aba_t old = { .freelist = freelist_old, .counter = tid };
+       freelist_aba_t new = { .freelist = freelist_new, .counter = next_tid(tid) };
+
+       return this_cpu_try_cmpxchg_freelist(s->cpu_slab->freelist_tid.full,
+                                            &old.full, new.full);
+}
+
 /*
  * Check the slab->freelist and either transfer the freelist to the
  * per cpu freelist or deactivate the slab.
@@ -3034,7 +3067,7 @@ static inline void *get_freelist(struct kmem_cache *s, struct slab *slab)
                new.inuse = slab->objects;
                new.frozen = freelist != NULL;
 
-       } while (!__cmpxchg_double_slab(s, slab,
+       } while (!__slab_update_freelist(s, slab,
                freelist, counters,
                NULL, new.counters,
                "get_freelist"));
@@ -3359,11 +3392,7 @@ redo:
                 * against code executing on this cpu *not* from access by
                 * other cpus.
                 */
-               if (unlikely(!this_cpu_cmpxchg_double(
-                               s->cpu_slab->freelist, s->cpu_slab->tid,
-                               object, tid,
-                               next_object, next_tid(tid)))) {
-
+               if (unlikely(!__update_cpu_freelist_fast(s, object, next_object, tid))) {
                        note_cmpxchg_failure("slab_alloc", s, tid);
                        goto redo;
                }
@@ -3631,7 +3660,7 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
                        }
                }
 
-       } while (!cmpxchg_double_slab(s, slab,
+       } while (!slab_update_freelist(s, slab,
                prior, counters,
                head, new.counters,
                "__slab_free"));
@@ -3736,11 +3765,7 @@ redo:
 
                set_freepointer(s, tail_obj, freelist);
 
-               if (unlikely(!this_cpu_cmpxchg_double(
-                               s->cpu_slab->freelist, s->cpu_slab->tid,
-                               freelist, tid,
-                               head, next_tid(tid)))) {
-
+               if (unlikely(!__update_cpu_freelist_fast(s, freelist, head, tid))) {
                        note_cmpxchg_failure("slab_free", s, tid);
                        goto redo;
                }
@@ -4505,11 +4530,11 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
                }
        }
 
-#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
-    defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
-       if (system_has_cmpxchg_double() && (s->flags & SLAB_NO_CMPXCHG) == 0)
+#ifdef system_has_freelist_aba
+       if (system_has_freelist_aba() && !(s->flags & SLAB_NO_CMPXCHG)) {
                /* Enable fast mode */
                s->flags |= __CMPXCHG_DOUBLE;
+       }
 #endif
 
        /*