Fix abd_enter/exit_critical wrappers

Commit fc551d7 introduced the wrappers abd_enter_critical() and
abd_exit_critical() to mark critical sections.  On Linux these are
implemented with the local_irq_save() and local_irq_restore() macros
which set the 'flags' argument when saving.  By wrapping them with
a function the local variable is no longer set by the macro and is
no longer properly restored.

Convert abd_enter_critical() and abd_exit_critical() to macros to
resolve this issue and ensure the flags are properly restored.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #10332

include/sys/abd_impl.h

@@ -98,8 +98,6 @@ void abd_update_scatter_stats(abd_t *, abd_stats_op_t);
 void abd_update_linear_stats(abd_t *, abd_stats_op_t);
 void abd_verify_scatter(abd_t *);
 void abd_free_linear_page(abd_t *);
-void abd_enter_critical(unsigned long);
-void abd_exit_critical(unsigned long);
 /* OS specific abd_iter functions */
 void abd_iter_init(struct abd_iter  *, abd_t *);
 boolean_t abd_iter_at_end(struct abd_iter *);
@@ -119,6 +117,19 @@ void abd_iter_unmap(struct abd_iter *);
 #define	ABD_SCATTER(abd)	(abd->abd_u.abd_scatter)
 #define	ABD_LINEAR_BUF(abd)	(abd->abd_u.abd_linear.abd_buf)
 
+#if defined(_KERNEL)
+#if defined(__FreeBSD__)
+#define	abd_enter_critical(flags)	critical_enter()
+#define	abd_exit_critical(flags)	critical_exit()
+#else
+#define	abd_enter_critical(flags)	local_irq_save(flags)
+#define	abd_exit_critical(flags)	local_irq_restore(flags)
+#endif
+#else /* !_KERNEL */
+#define	abd_enter_critical(flags)	((void)0)
+#define	abd_exit_critical(flags)	((void)0)
+#endif
+
 #ifdef __cplusplus
 }
 #endif

module/os/freebsd/zfs/abd_os.c

@@ -419,15 +419,3 @@ abd_iter_unmap(struct abd_iter *aiter)
 	aiter->iter_mapaddr = NULL;
 	aiter->iter_mapsize = 0;
 }
-
-void
-abd_enter_critical(unsigned long flags)
-{
-	critical_enter();
-}
-
-void
-abd_exit_critical(unsigned long flags)
-{
-	critical_exit();
-}

module/os/linux/zfs/abd_os.c

@@ -803,18 +803,6 @@ abd_iter_unmap(struct abd_iter *aiter)
 	aiter->iter_mapsize = 0;
 }
 
-void
-abd_enter_critical(unsigned long flags)
-{
-	local_irq_save(flags);
-}
-
-void
-abd_exit_critical(unsigned long flags)
-{
-	local_irq_restore(flags);
-}
-
 #if defined(_KERNEL)
 /*
  * bio_nr_pages for ABD.

module/zfs/abd.c

@@ -703,7 +703,7 @@ abd_raidz_gen_iterate(abd_t **cabds, abd_t *dabd,
 	struct abd_iter caiters[3];
 	struct abd_iter daiter = {0};
 	void *caddrs[3];
-	unsigned long flags = 0;
+	unsigned long flags __maybe_unused = 0;
 
 	ASSERT3U(parity, <=, 3);
 
@@ -800,7 +800,7 @@ abd_raidz_rec_iterate(abd_t **cabds, abd_t **tabds,
 	struct abd_iter citers[3];
 	struct abd_iter xiters[3];
 	void *caddrs[3], *xaddrs[3];
-	unsigned long flags = 0;
+	unsigned long flags __maybe_unused = 0;
 
 	ASSERT3U(parity, <=, 3);