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Use more atomics in refcounts 

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>
Closes #12420
This commit is contained in:
Alexander Motin 2021-08-17 11:44:34 -04:00 committed by Tony Hutter
parent c6c0d30016
commit 5afc35b698
2 changed files with 26 additions and 33 deletions
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8
include/sys/zfs_refcount.h
View File

@ -96,8 +96,8 @@ typedef struct refcount {
#define zfs_refcount_create_tracked(rc) ((rc)->rc_count = 0) #define zfs_refcount_create_tracked(rc) ((rc)->rc_count = 0)
#define zfs_refcount_destroy(rc) ((rc)->rc_count = 0) #define zfs_refcount_destroy(rc) ((rc)->rc_count = 0)
#define zfs_refcount_destroy_many(rc, number) ((rc)->rc_count = 0) #define zfs_refcount_destroy_many(rc, number) ((rc)->rc_count = 0)
#define zfs_refcount_is_zero(rc) ((rc)->rc_count == 0) #define zfs_refcount_is_zero(rc) (zfs_refcount_count(rc) == 0)
#define zfs_refcount_count(rc) ((rc)->rc_count) #define zfs_refcount_count(rc) atomic_load_64(&(rc)->rc_count)
#define zfs_refcount_add(rc, holder) atomic_inc_64_nv(&(rc)->rc_count) #define zfs_refcount_add(rc, holder) atomic_inc_64_nv(&(rc)->rc_count)
#define zfs_refcount_remove(rc, holder) atomic_dec_64_nv(&(rc)->rc_count) #define zfs_refcount_remove(rc, holder) atomic_dec_64_nv(&(rc)->rc_count)
#define zfs_refcount_add_many(rc, number, holder) \ #define zfs_refcount_add_many(rc, number, holder) \
@ -105,13 +105,13 @@ typedef struct refcount {
#define zfs_refcount_remove_many(rc, number, holder) \ #define zfs_refcount_remove_many(rc, number, holder) \
atomic_add_64_nv(&(rc)->rc_count, -number) atomic_add_64_nv(&(rc)->rc_count, -number)
#define zfs_refcount_transfer(dst, src) { \ #define zfs_refcount_transfer(dst, src) { \
uint64_t __tmp = (src)->rc_count; \ uint64_t __tmp = zfs_refcount_count(src); \
atomic_add_64(&(src)->rc_count, -__tmp); \ atomic_add_64(&(src)->rc_count, -__tmp); \
atomic_add_64(&(dst)->rc_count, __tmp); \ atomic_add_64(&(dst)->rc_count, __tmp); \
} }
#define zfs_refcount_transfer_ownership(rc, ch, nh) ((void)0) #define zfs_refcount_transfer_ownership(rc, ch, nh) ((void)0)
#define zfs_refcount_transfer_ownership_many(rc, nr, ch, nh) ((void)0) #define zfs_refcount_transfer_ownership_many(rc, nr, ch, nh) ((void)0)
#define zfs_refcount_held(rc, holder) ((rc)->rc_count > 0) #define zfs_refcount_held(rc, holder) (zfs_refcount_count(rc) > 0)
#define zfs_refcount_not_held(rc, holder) (B_TRUE) #define zfs_refcount_not_held(rc, holder) (B_TRUE)
#define zfs_refcount_init() #define zfs_refcount_init()

45
module/zfs/refcount.c
View File

@ -112,13 +112,13 @@ zfs_refcount_destroy(zfs_refcount_t *rc)
int int
zfs_refcount_is_zero(zfs_refcount_t *rc) zfs_refcount_is_zero(zfs_refcount_t *rc)
{ {
return (rc->rc_count == 0); return (zfs_refcount_count(rc) == 0);
} }
int64_t int64_t
zfs_refcount_count(zfs_refcount_t *rc) zfs_refcount_count(zfs_refcount_t *rc)
{ {
return (rc->rc_count); return (atomic_load_64(&rc->rc_count));
} }
int64_t int64_t
@ -127,14 +127,17 @@ zfs_refcount_add_many(zfs_refcount_t *rc, uint64_t number, const void *holder)
reference_t *ref = NULL; reference_t *ref = NULL;
int64_t count; int64_t count;
if (rc->rc_tracked) { 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 = kmem_cache_alloc(reference_cache, KM_SLEEP);
ref->ref_holder = holder; ref->ref_holder = holder;
ref->ref_number = number; ref->ref_number = number;
}
mutex_enter(&rc->rc_mtx); mutex_enter(&rc->rc_mtx);
ASSERT3U(rc->rc_count, >=, 0); 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; rc->rc_count += number;
count = rc->rc_count; count = rc->rc_count;
@ -156,16 +159,14 @@ zfs_refcount_remove_many(zfs_refcount_t *rc, uint64_t number,
reference_t *ref; reference_t *ref;
int64_t count; int64_t count;
mutex_enter(&rc->rc_mtx);
ASSERT3U(rc->rc_count, >=, number);
if (!rc->rc_tracked) { if (!rc->rc_tracked) {
rc->rc_count -= number; count = atomic_add_64_nv(&(rc)->rc_count, -number);
count = rc->rc_count; ASSERT3S(count, >=, 0);
mutex_exit(&rc->rc_mtx);
return (count); return (count);
} }
mutex_enter(&rc->rc_mtx);
ASSERT3U(rc->rc_count, >=, number);
for (ref = list_head(&rc->rc_list); ref; for (ref = list_head(&rc->rc_list); ref;
ref = list_next(&rc->rc_list, ref)) { ref = list_next(&rc->rc_list, ref)) {
if (ref->ref_holder == holder && ref->ref_number == number) { 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; reference_t *ref;
boolean_t found = B_FALSE; boolean_t found = B_FALSE;
mutex_enter(&rc->rc_mtx); if (!rc->rc_tracked)
if (!rc->rc_tracked) {
mutex_exit(&rc->rc_mtx);
return; return;
}
mutex_enter(&rc->rc_mtx);
for (ref = list_head(&rc->rc_list); ref; for (ref = list_head(&rc->rc_list); ref;
ref = list_next(&rc->rc_list, ref)) { ref = list_next(&rc->rc_list, ref)) {
if (ref->ref_holder == current_holder && if (ref->ref_holder == current_holder &&
@ -279,13 +278,10 @@ zfs_refcount_held(zfs_refcount_t *rc, const void *holder)
{ {
reference_t *ref; reference_t *ref;
if (!rc->rc_tracked)
return (zfs_refcount_count(rc) > 0);
mutex_enter(&rc->rc_mtx); 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; for (ref = list_head(&rc->rc_list); ref;
ref = list_next(&rc->rc_list, ref)) { ref = list_next(&rc->rc_list, ref)) {
if (ref->ref_holder == holder) { if (ref->ref_holder == holder) {
@ -307,13 +303,10 @@ zfs_refcount_not_held(zfs_refcount_t *rc, const void *holder)
{ {
reference_t *ref; reference_t *ref;
mutex_enter(&rc->rc_mtx); if (!rc->rc_tracked)
if (!rc->rc_tracked) {
mutex_exit(&rc->rc_mtx);
return (B_TRUE); return (B_TRUE);
}
mutex_enter(&rc->rc_mtx);
for (ref = list_head(&rc->rc_list); ref; for (ref = list_head(&rc->rc_list); ref;
ref = list_next(&rc->rc_list, ref)) { ref = list_next(&rc->rc_list, ref)) {
if (ref->ref_holder == holder) { if (ref->ref_holder == holder) {