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MINOR: memory: Change the flush_lock to a spinlock, and don't get it in alloc.

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The flush_lock was introduced, mostly to be sure that pool_gc() will never
dereference a pointer that has been free'd. __pool_get_first() was acquiring
the lock to, the fear was that otherwise that pointer could get free'd later,
and then pool_gc() would attempt to dereference it. However, that can not
happen, because the only functions that can free a pointer, when using
lockless pools, are pool_gc() and pool_flush(), and as long as those two
are mutually exclusive, nobody will be able to free the pointer while
pool_gc() attempts to access it.
So change the flush_lock to a spinlock, and don't bother acquire/release
it in __pool_get_first(), that way callers of __pool_get_first() won't have
to wait while the pool is flushed. The worst that can happen is we call
__pool_refill_alloc() while the pool is getting flushed, and memory can
get allocated just to be free'd.

This may help with github issue #552

This may be backported to 2.1, 2.0 and 1.9.
This commit is contained in:
Olivier Houchard 2020-03-18 15:48:29 +01:00
parent b0198cc413
commit 899fb8abdc
2 changed files with 7 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/common/memory.h
View File

@ -78,7 +78,7 @@ struct pool_head {
void **free_list;
#ifdef CONFIG_HAP_LOCKLESS_POOLS
uintptr_t seq;
HA_RWLOCK_T flush_lock;
HA_SPINLOCK_T flush_lock;
#else
__decl_hathreads(HA_SPINLOCK_T lock); /* the spin lock */
#endif
@ -222,19 +222,15 @@ static inline void *__pool_get_first(struct pool_head *pool)
cmp.seq = pool->seq;
__ha_barrier_load();
HA_RWLOCK_RDLOCK(POOL_LOCK, &pool->flush_lock);
cmp.free_list = pool->free_list;
do {
if (cmp.free_list == NULL) {
HA_RWLOCK_RDUNLOCK(POOL_LOCK, &pool->flush_lock);
if (cmp.free_list == NULL)
return NULL;
}
new.seq = cmp.seq + 1;
__ha_barrier_load();
new.free_list = *POOL_LINK(pool, cmp.free_list);
} while (HA_ATOMIC_DWCAS((void *)&pool->free_list, (void *)&cmp, (void *)&new) == 0);
__ha_barrier_atomic_store();
HA_RWLOCK_RDUNLOCK(POOL_LOCK, &pool->flush_lock);
_HA_ATOMIC_ADD(&pool->used, 1);
#ifdef DEBUG_MEMORY_POOLS

10
src/memory.c
View File

@ -142,7 +142,7 @@ struct pool_head *create_pool(char *name, unsigned int size, unsigned int flags)
#ifndef CONFIG_HAP_LOCKLESS_POOLS
HA_SPIN_INIT(&pool->lock);
#else
HA_RWLOCK_INIT(&pool->flush_lock);
HA_SPIN_INIT(&pool->flush_lock);
#endif
}
pool->users++;
@ -225,7 +225,7 @@ void pool_flush(struct pool_head *pool)
if (!pool)
return;
HA_RWLOCK_WRLOCK(POOL_LOCK, &pool->flush_lock);
HA_SPIN_LOCK(POOL_LOCK, &pool->flush_lock);
do {
cmp.free_list = pool->free_list;
cmp.seq = pool->seq;
@ -233,7 +233,7 @@ void pool_flush(struct pool_head *pool)
new.seq = cmp.seq + 1;
} while (!_HA_ATOMIC_DWCAS(&pool->free_list, &cmp, &new));
__ha_barrier_atomic_store();
HA_RWLOCK_WRUNLOCK(POOL_LOCK, &pool->flush_lock);
HA_SPIN_UNLOCK(POOL_LOCK, &pool->flush_lock);
next = cmp.free_list;
while (next) {
temp = next;
@ -263,7 +263,7 @@ void pool_gc(struct pool_head *pool_ctx)
return;
list_for_each_entry(entry, &pools, list) {
HA_RWLOCK_WRLOCK(POOL_LOCK, &entry->flush_lock);
HA_SPIN_LOCK(POOL_LOCK, &entry->flush_lock);
while ((int)((volatile int)entry->allocated - (volatile int)entry->used) > (int)entry->minavail) {
struct pool_free_list cmp, new;
@ -280,7 +280,7 @@ void pool_gc(struct pool_head *pool_ctx)
free(cmp.free_list);
_HA_ATOMIC_SUB(&entry->allocated, 1);
}
HA_RWLOCK_WRUNLOCK(POOL_LOCK, &entry->flush_lock);
HA_SPIN_UNLOCK(POOL_LOCK, &entry->flush_lock);
}
_HA_ATOMIC_STORE(&recurse, 0);