svn commit: r356120 - head/sys/security/mac

[Mateusz Guzik]

Author: mjg
Date: Fri Dec 27 11:23:32 2019
New Revision: 356120
URL: https://svnweb.freebsd.org/changeset/base/356120

Log:
  mac: use a sleepable rmlock instead of an sx lock
  
  If any non-static modules are loaded (and mac_ntpd tends to be), the lock is
  taken all the time al over the kernel. On platforms like arm64 this results in
  an avoidable significant performance degradation. Since write-locking is almost
  never needed, use a primitive optimized towards read-locking.
  
  Sample result of building the kernel on tmpfs 11 times:
  stock           11142.80s user 6704.44s system 4924% cpu 6:02.42 total
  patched         11118.95s user 2374.94s system 4547% cpu 4:56.71 total

Modified:
  head/sys/security/mac/mac_framework.c

Modified: head/sys/security/mac/mac_framework.c
==============================================================================
--- head/sys/security/mac/mac_framework.c	Fri Dec 27 11:19:57 2019	(r356119)
+++ head/sys/security/mac/mac_framework.c	Fri Dec 27 11:23:32 2019	(r356120)
@@ -176,6 +176,7 @@ MALLOC_DEFINE(M_MACTEMP, "mactemp", "MAC temporary lab
 #ifndef MAC_STATIC
 static struct rmlock mac_policy_rm;	/* Non-sleeping entry points. */
 static struct sx mac_policy_sx;		/* Sleeping entry points. */
+static struct rmslock mac_policy_rms;
 #endif
 
 struct mac_policy_list_head mac_policy_list;
@@ -209,7 +210,7 @@ mac_policy_slock_sleep(void)
 	if (!mac_late)
 		return;
 
-	sx_slock(&mac_policy_sx);
+	rms_rlock(&mac_policy_rms);
 #endif
 }
 
@@ -233,7 +234,7 @@ mac_policy_sunlock_sleep(void)
 	if (!mac_late)
 		return;
 
-	sx_sunlock(&mac_policy_sx);
+	rms_runlock(&mac_policy_rms);
 #endif
 }
 
@@ -249,6 +250,7 @@ mac_policy_xlock(void)
 		return;
 
 	sx_xlock(&mac_policy_sx);
+	rms_wlock(&mac_policy_rms);
 	rm_wlock(&mac_policy_rm);
 #endif
 }
@@ -262,6 +264,7 @@ mac_policy_xunlock(void)
 		return;
 
 	rm_wunlock(&mac_policy_rm);
+	rms_wunlock(&mac_policy_rms);
 	sx_xunlock(&mac_policy_sx);
 #endif
 }
@@ -294,6 +297,7 @@ mac_init(void)
 	rm_init_flags(&mac_policy_rm, "mac_policy_rm", RM_NOWITNESS |
 	    RM_RECURSE);
 	sx_init_flags(&mac_policy_sx, "mac_policy_sx", SX_NOWITNESS);
+	rms_init(&mac_policy_rms, "mac_policy_rms");
 #endif
 }