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Use more atomics in refcounts

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Use atomic_load_64() for zfs_refcount_count() to prevent torn reads
on 32-bit platforms.  On 64-bit ones it should not change anything.

When built with ZFS_DEBUG but running without tracking enabled use
atomics instead of mutexes same as for builds without ZFS_DEBUG.
Since rc_tracked can't change live we can check it without lock.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #12420
This commit is contained in:
Alexander Motin
2021-08-17 11:44:34 -04:00
committed by GitHub
parent 5bfc3a99f9
commit e829a865bf
2 changed files with 26 additions and 33 deletions
Download Patch File Download Diff File Expand all files Collapse all files
module/zfs/refcount.c
+22 -29
View File
@@ -112,13 +112,13 @@ zfs_refcount_destroy(zfs_refcount_t *rc)
int
zfs_refcount_is_zero(zfs_refcount_t *rc)
{
return (rc->rc_count == 0);
return (zfs_refcount_count(rc) == 0);
}
int64_t
zfs_refcount_count(zfs_refcount_t *rc)
{
return (rc->rc_count);
return (atomic_load_64(&rc->rc_count));
}
int64_t
@@ -127,15 +127,18 @@ zfs_refcount_add_many(zfs_refcount_t *rc, uint64_t number, const void *holder)
reference_t *ref = NULL;
int64_t count;
if (rc->rc_tracked) {
ref = kmem_cache_alloc(reference_cache, KM_SLEEP);
ref->ref_holder = holder;
ref->ref_number = number;
if (!rc->rc_tracked) {
count = atomic_add_64_nv(&(rc)->rc_count, number);
ASSERT3U(count, >=, number);
return (count);
}
ref = kmem_cache_alloc(reference_cache, KM_SLEEP);
ref->ref_holder = holder;
ref->ref_number = number;
mutex_enter(&rc->rc_mtx);
ASSERT3U(rc->rc_count, >=, 0);
if (rc->rc_tracked)
list_insert_head(&rc->rc_list, ref);
list_insert_head(&rc->rc_list, ref);
rc->rc_count += number;
count = rc->rc_count;
mutex_exit(&rc->rc_mtx);
@@ -156,16 +159,14 @@ zfs_refcount_remove_many(zfs_refcount_t *rc, uint64_t number,
reference_t *ref;
int64_t count;
mutex_enter(&rc->rc_mtx);
ASSERT3U(rc->rc_count, >=, number);
if (!rc->rc_tracked) {
rc->rc_count -= number;
count = rc->rc_count;
mutex_exit(&rc->rc_mtx);
count = atomic_add_64_nv(&(rc)->rc_count, -number);
ASSERT3S(count, >=, 0);
return (count);
}
mutex_enter(&rc->rc_mtx);
ASSERT3U(rc->rc_count, >=, number);
for (ref = list_head(&rc->rc_list); ref;
ref = list_next(&rc->rc_list, ref)) {
if (ref->ref_holder == holder && ref->ref_number == number) {
@@ -242,12 +243,10 @@ zfs_refcount_transfer_ownership_many(zfs_refcount_t *rc, uint64_t number,
reference_t *ref;
boolean_t found = B_FALSE;
mutex_enter(&rc->rc_mtx);
if (!rc->rc_tracked) {
mutex_exit(&rc->rc_mtx);
if (!rc->rc_tracked)
return;
}
mutex_enter(&rc->rc_mtx);
for (ref = list_head(&rc->rc_list); ref;
ref = list_next(&rc->rc_list, ref)) {
if (ref->ref_holder == current_holder &&
@@ -279,13 +278,10 @@ zfs_refcount_held(zfs_refcount_t *rc, const void *holder)
{
reference_t *ref;
if (!rc->rc_tracked)
return (zfs_refcount_count(rc) > 0);
mutex_enter(&rc->rc_mtx);
if (!rc->rc_tracked) {
mutex_exit(&rc->rc_mtx);
return (rc->rc_count > 0);
}
for (ref = list_head(&rc->rc_list); ref;
ref = list_next(&rc->rc_list, ref)) {
if (ref->ref_holder == holder) {
@@ -307,13 +303,10 @@ zfs_refcount_not_held(zfs_refcount_t *rc, const void *holder)
{
reference_t *ref;
mutex_enter(&rc->rc_mtx);
if (!rc->rc_tracked) {
mutex_exit(&rc->rc_mtx);
if (!rc->rc_tracked)
return (B_TRUE);
}
mutex_enter(&rc->rc_mtx);
for (ref = list_head(&rc->rc_list); ref;
ref = list_next(&rc->rc_list, ref)) {
if (ref->ref_holder == holder) {