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Date:      Thu, 16 Jul 2020 14:09:18 +0000 (UTC)
From:      Mateusz Guzik <mjg@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r363249 - in head/sys: kern security/mac
Message-ID:  <202007161409.06GE9Ihc045261@repo.freebsd.org>
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Author: mjg
Date: Thu Jul 16 14:09:18 2020
New Revision: 363249
URL: https://svnweb.freebsd.org/changeset/base/363249

Log:
  vfs: fix vn_poll performance with either MAC or AUDIT
  
  The code would unconditionally lock the vnode to audit or call the
  mac hoook, even if neither want to do anything. Pre-check the state
  to avoid locking in the common case of nothing to do.
  
  Note this code should not be normally executed anyway as vnodes are
  always return ready. However, poll1/2 from will-it-scale use regular
  files for benchmarking, presumably to focus on the interface itself
  as the vnode handler is not supposed to do almost anything.
  
  This in particular fixes poll2 which passes 128 fds.
  
  $ ./poll2_processes -s 10
  before: 134411
  after:  271572

Modified:
  head/sys/kern/vfs_vnops.c
  head/sys/security/mac/mac_framework.c
  head/sys/security/mac/mac_framework.h

Modified: head/sys/kern/vfs_vnops.c
==============================================================================
--- head/sys/kern/vfs_vnops.c	Thu Jul 16 14:04:29 2020	(r363248)
+++ head/sys/kern/vfs_vnops.c	Thu Jul 16 14:09:18 2020	(r363249)
@@ -1636,12 +1636,14 @@ vn_poll(struct file *fp, int events, struct ucred *act
 
 	vp = fp->f_vnode;
 #if defined(MAC) || defined(AUDIT)
-	vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
-	AUDIT_ARG_VNODE1(vp);
-	error = mac_vnode_check_poll(active_cred, fp->f_cred, vp);
-	VOP_UNLOCK(vp);
-	if (error != 0)
-		return (error);
+	if (AUDITING_TD(td) || mac_vnode_check_poll_enabled()) {
+		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+		AUDIT_ARG_VNODE1(vp);
+		error = mac_vnode_check_poll(active_cred, fp->f_cred, vp);
+		VOP_UNLOCK(vp);
+		if (error != 0)
+			return (error);
+	}
 #endif
 	error = VOP_POLL(vp, events, fp->f_cred, td);
 	return (error);

Modified: head/sys/security/mac/mac_framework.c
==============================================================================
--- head/sys/security/mac/mac_framework.c	Thu Jul 16 14:04:29 2020	(r363248)
+++ head/sys/security/mac/mac_framework.c	Thu Jul 16 14:09:18 2020	(r363249)
@@ -118,11 +118,18 @@ SYSCTL_UINT(_security_mac, OID_AUTO, version, CTLFLAG_
     "");
 
 /*
- * Flags for inlined checks.
+ * Flags for inlined checks. Note this would be best hotpatched at runtime.
+ * The following is a band-aid.
+ *
+ * Use FPFLAG for hooks running in commonly executed paths and FPFLAG_RARE
+ * for the rest.
  */
 #define FPFLAG(f)	\
 bool __read_frequently mac_##f##_fp_flag
 
+#define FPFLAG_RARE(f)	\
+bool __read_mostly mac_##f##_fp_flag
+
 FPFLAG(priv_check);
 FPFLAG(priv_grant);
 FPFLAG(vnode_check_lookup);
@@ -131,8 +138,10 @@ FPFLAG(vnode_check_stat);
 FPFLAG(vnode_check_read);
 FPFLAG(vnode_check_write);
 FPFLAG(vnode_check_mmap);
+FPFLAG_RARE(vnode_check_poll);
 
 #undef FPFLAG
+#undef FPFLAG_RARE
 
 /*
  * Labels consist of a indexed set of "slots", which are allocated policies
@@ -416,6 +425,8 @@ struct mac_policy_fastpath_elem mac_policy_fastpath_ar
 		.flag = &mac_vnode_check_write_fp_flag },
 	{ .offset = FPO(vnode_check_mmap),
 		.flag = &mac_vnode_check_mmap_fp_flag },
+	{ .offset = FPO(vnode_check_poll),
+		.flag = &mac_vnode_check_poll_fp_flag },
 };
 
 static void

Modified: head/sys/security/mac/mac_framework.h
==============================================================================
--- head/sys/security/mac/mac_framework.h	Thu Jul 16 14:04:29 2020	(r363248)
+++ head/sys/security/mac/mac_framework.h	Thu Jul 16 14:09:18 2020	(r363249)
@@ -463,10 +463,14 @@ mac_vnode_check_open(struct ucred *cred, struct vnode 
 
 int	mac_vnode_check_mprotect(struct ucred *cred, struct vnode *vp,
 	    int prot);
+
+#define mac_vnode_check_poll_enabled() __predict_false(mac_vnode_check_poll_fp_flag)
 #ifdef MAC
+extern bool mac_vnode_check_poll_fp_flag;
 int	mac_vnode_check_poll(struct ucred *active_cred,
 	    struct ucred *file_cred, struct vnode *vp);
 #else
+#define mac_vnode_check_poll_fp_flag	0
 static inline int
 mac_vnode_check_poll(struct ucred *active_cred, struct ucred *file_cred,
     struct vnode *vp)

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