Skip dbuf_evict_one() from dbuf_evict_notify() for reclaim thread

Avoid calling dbuf_evict_one() from memory reclaim contexts (e.g. Linux
kswapd, FreeBSD pagedaemon). This prevents deadlock caused by reclaim
threads waiting for the dbuf hash lock in the call sequence:
dbuf_evict_one -> dbuf_destroy -> arc_buf_destroy

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Signed-off-by: Kaitlin Hoang <kthoang@amazon.com>
Closes #17561

module/os/freebsd/spl/spl_misc.c

@@ -101,6 +101,15 @@ spl_panic(const char *file, const char *func, int line, const char *fmt, ...)
 	va_end(ap);
 }
 
+/*
+ * Check if the current thread is a memory reclaim thread.
+ * Returns true if curproc is pageproc (FreeBSD's page daemon).
+ */
+int
+current_is_reclaim_thread(void)
+{
+	return (curproc == pageproc);
+}
 
 SYSINIT(opensolaris_utsname_init, SI_SUB_TUNABLES, SI_ORDER_ANY,
     opensolaris_utsname_init, NULL);