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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>
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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include/sys/zfs_refcount.h
+4 -4
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@@ -96,8 +96,8 @@ typedef struct refcount {
#define zfs_refcount_create_tracked(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_is_zero(rc) ((rc)->rc_count == 0)
#define zfs_refcount_count(rc) ((rc)->rc_count)
#define zfs_refcount_is_zero(rc) (zfs_refcount_count(rc) == 0)
#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_remove(rc, holder) atomic_dec_64_nv(&(rc)->rc_count)
#define zfs_refcount_add_many(rc, number, holder) \
@@ -105,13 +105,13 @@ typedef struct refcount {
#define zfs_refcount_remove_many(rc, number, holder) \
atomic_add_64_nv(&(rc)->rc_count, -number)
#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(&(dst)->rc_count, __tmp); \
}
#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_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_init()