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Date:      Thu, 26 Nov 2020 18:00:26 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r368073 - in head/sys: kern sys
Message-ID:  <202011261800.0AQI0Qgq025291@repo.freebsd.org>
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Author: kib
Date: Thu Nov 26 18:00:26 2020
New Revision: 368073
URL: https://svnweb.freebsd.org/changeset/base/368073

Log:
  Make max ticks for pause in vn_lock_pair() adjustable at runtime.
  
  Reduce default value from hz / 10 to hz / 100.
  
  Reviewed by:	markj
  Tested by:	pho
  Sponsored by:	The FreeBSD Foundation

Modified:
  head/sys/kern/subr_param.c
  head/sys/kern/vfs_vnops.c
  head/sys/sys/vnode.h

Modified: head/sys/kern/subr_param.c
==============================================================================
--- head/sys/kern/subr_param.c	Thu Nov 26 17:39:51 2020	(r368072)
+++ head/sys/kern/subr_param.c	Thu Nov 26 18:00:26 2020	(r368073)
@@ -51,6 +51,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/msgbuf.h>
 #include <sys/sysctl.h>
 #include <sys/proc.h>
+#include <sys/vnode.h>
 
 #include <vm/vm.h>
 #include <vm/vm_param.h>
@@ -183,6 +184,10 @@ init_param1(void)
 	 * sign problems sooner.
 	 */
 	ticks = INT_MAX - (hz * 10 * 60);
+
+	vn_lock_pair_pause_max = hz / 100;
+	if (vn_lock_pair_pause_max == 0)
+		vn_lock_pair_pause_max = 1;
 
 #ifdef VM_SWZONE_SIZE_MAX
 	maxswzone = VM_SWZONE_SIZE_MAX;

Modified: head/sys/kern/vfs_vnops.c
==============================================================================
--- head/sys/kern/vfs_vnops.c	Thu Nov 26 17:39:51 2020	(r368072)
+++ head/sys/kern/vfs_vnops.c	Thu Nov 26 18:00:26 2020	(r368073)
@@ -3332,11 +3332,16 @@ SYSCTL_ULONG(_debug, OID_AUTO, vn_lock_pair_pause, CTL
     &vn_lock_pair_pause_cnt, 0,
     "Count of vn_lock_pair deadlocks");
 
+u_int vn_lock_pair_pause_max;
+SYSCTL_UINT(_debug, OID_AUTO, vn_lock_pair_pause_max, CTLFLAG_RW,
+    &vn_lock_pair_pause_max, 0,
+    "Max ticks for vn_lock_pair deadlock avoidance sleep");
+
 static void
 vn_lock_pair_pause(const char *wmesg)
 {
 	atomic_add_long(&vn_lock_pair_pause_cnt, 1);
-	pause(wmesg, prng32_bounded(hz / 10));
+	pause(wmesg, prng32_bounded(vn_lock_pair_pause_max));
 }
 
 /*

Modified: head/sys/sys/vnode.h
==============================================================================
--- head/sys/sys/vnode.h	Thu Nov 26 17:39:51 2020	(r368072)
+++ head/sys/sys/vnode.h	Thu Nov 26 18:00:26 2020	(r368073)
@@ -448,6 +448,8 @@ extern	u_long desiredvnodes;		/* number of vnodes desi
 extern	struct uma_zone *namei_zone;
 extern	struct vattr va_null;		/* predefined null vattr structure */
 
+extern	u_int vn_lock_pair_pause_max;
+
 #define	VI_LOCK(vp)	mtx_lock(&(vp)->v_interlock)
 #define	VI_LOCK_FLAGS(vp, flags) mtx_lock_flags(&(vp)->v_interlock, (flags))
 #define	VI_TRYLOCK(vp)	mtx_trylock(&(vp)->v_interlock)

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