Cleanup: Correct memory barrier definitions

We inherited membar_consumer() and membar_producer() from OpenSolaris, but we had replaced membar_consumer() with Linux's smp_rmb() in zfs_ioctl.c. The FreeBSD SPL consequently implemented a shim for the Linux-only smp_rmb(). Additionally, FreeBSD implemented membar_producer() as a full memory barrier, rather than a store memory barrier. We reinstate membar_consumer() in platform independent code and at the same time, correct the FreeBSD definition to be a store memory barrier. Signed-off-by: Richard Yao <[email protected]>
openzfs · Sep 6, 2022 · fdf5c3f · fdf5c3f
1 parent 5976747
commit fdf5c3f
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Showing 4 changed files with 4 additions and 3 deletions.
diff --git a/include/os/freebsd/linux/compiler.h b/include/os/freebsd/linux/compiler.h
@@ -83,7 +83,6 @@
 #define	__printf(a, b)			__printflike(a, b)
 
 #define	barrier()			__asm__ __volatile__("": : :"memory")
-#define	smp_rmb()		rmb()
 #define	___PASTE(a, b) a##b
 #define	__PASTE(a, b) ___PASTE(a, b)
 

diff --git a/include/os/freebsd/spl/sys/atomic.h b/include/os/freebsd/spl/sys/atomic.h
@@ -57,7 +57,8 @@ extern uint64_t atomic_cas_64(volatile uint64_t *target, uint64_t cmp,
     uint64_t newval);
 #endif
 
-#define	membar_producer	atomic_thread_fence_rel
+#define	membar_consumer()		rmb()
+#define	membar_producer()		wmb()
 
 static __inline uint32_t
 atomic_add_32_nv(volatile uint32_t *target, int32_t delta)

diff --git a/include/os/linux/spl/sys/vmsystm.h b/include/os/linux/spl/sys/vmsystm.h
@@ -45,6 +45,7 @@
 #endif
 
 #define	membar_producer()		smp_wmb()
+#define	membar_consumer()		smp_rmb()
 #define	physmem				zfs_totalram_pages
 
 #define	xcopyin(from, to, size)		copy_from_user(to, from, size)

diff --git a/module/zfs/zfs_ioctl.c b/module/zfs/zfs_ioctl.c
@@ -7482,7 +7482,7 @@ zfsdev_get_state(minor_t minor, enum zfsdev_state_type which)
 
 	for (zs = zfsdev_state_list; zs != NULL; zs = zs->zs_next) {
 		if (zs->zs_minor == minor) {
-			smp_rmb();
+			membar_consumer();
 			switch (which) {
 			case ZST_ONEXIT:
 				return (zs->zs_onexit);