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Date:      Sun, 22 May 2016 23:25:01 +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: r300439 - head/sys/vm
Message-ID:  <201605222325.u4MNP1vo071364@repo.freebsd.org>
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Author: kib
Date: Sun May 22 23:25:01 2016
New Revision: 300439
URL: https://svnweb.freebsd.org/changeset/base/300439

Log:
  Replace hand-made exclusive lock, protecting against parallel
  swapon/swapoff invocations, with sx.
  
  Reviewed by:	alc (as part of larger patch)
  Sponsored by:	The FreeBSD Foundation

Modified:
  head/sys/vm/swap_pager.c

Modified: head/sys/vm/swap_pager.c
==============================================================================
--- head/sys/vm/swap_pager.c	Sun May 22 21:31:20 2016	(r300438)
+++ head/sys/vm/swap_pager.c	Sun May 22 23:25:01 2016	(r300439)
@@ -152,7 +152,7 @@ static TAILQ_HEAD(, swdevt) swtailq = TA
 static struct swdevt *swdevhd;	/* Allocate from here next */
 static int nswapdev;		/* Number of swap devices */
 int swap_pager_avail;
-static int swdev_syscall_active = 0; /* serialize swap(on|off) */
+static struct sx swdev_syscall_lock;	/* serialize swap(on|off) */
 
 static vm_ooffset_t swap_total;
 SYSCTL_QUAD(_vm, OID_AUTO, swap_total, CTLFLAG_RD, &swap_total, 0,
@@ -487,6 +487,7 @@ swap_pager_init(void)
 		TAILQ_INIT(&swap_pager_object_list[i]);
 	mtx_init(&sw_alloc_mtx, "swap_pager list", NULL, MTX_DEF);
 	mtx_init(&sw_dev_mtx, "swapdev", NULL, MTX_DEF);
+	sx_init(&swdev_syscall_lock, "swsysc");
 
 	/*
 	 * Device Stripe, in PAGE_SIZE'd blocks
@@ -1664,7 +1665,7 @@ swap_pager_swapoff(struct swdevt *sp)
 	struct swblock *swap;
 	int i, j, retries;
 
-	GIANT_REQUIRED;
+	sx_assert(&swdev_syscall_lock, SA_XLOCKED);
 
 	retries = 0;
 full_rescan:
@@ -2005,10 +2006,7 @@ sys_swapon(struct thread *td, struct swa
 	if (error)
 		return (error);
 
-	mtx_lock(&Giant);
-	while (swdev_syscall_active)
-	    tsleep(&swdev_syscall_active, PUSER - 1, "swpon", 0);
-	swdev_syscall_active = 1;
+	sx_xlock(&swdev_syscall_lock);
 
 	/*
 	 * Swap metadata may not fit in the KVM if we have physical
@@ -2043,9 +2041,7 @@ sys_swapon(struct thread *td, struct swa
 	if (error)
 		vrele(vp);
 done:
-	swdev_syscall_active = 0;
-	wakeup_one(&swdev_syscall_active);
-	mtx_unlock(&Giant);
+	sx_xunlock(&swdev_syscall_lock);
 	return (error);
 }
 
@@ -2175,10 +2171,7 @@ sys_swapoff(struct thread *td, struct sw
 	if (error)
 		return (error);
 
-	mtx_lock(&Giant);
-	while (swdev_syscall_active)
-	    tsleep(&swdev_syscall_active, PUSER - 1, "swpoff", 0);
-	swdev_syscall_active = 1;
+	sx_xlock(&swdev_syscall_lock);
 
 	NDINIT(&nd, LOOKUP, FOLLOW | AUDITVNODE1, UIO_USERSPACE, uap->name,
 	    td);
@@ -2200,9 +2193,7 @@ sys_swapoff(struct thread *td, struct sw
 	}
 	error = swapoff_one(sp, td->td_ucred);
 done:
-	swdev_syscall_active = 0;
-	wakeup_one(&swdev_syscall_active);
-	mtx_unlock(&Giant);
+	sx_xunlock(&swdev_syscall_lock);
 	return (error);
 }
 
@@ -2214,7 +2205,7 @@ swapoff_one(struct swdevt *sp, struct uc
 	int error;
 #endif
 
-	mtx_assert(&Giant, MA_OWNED);
+	sx_assert(&swdev_syscall_lock, SA_XLOCKED);
 #ifdef MAC
 	(void) vn_lock(sp->sw_vp, LK_EXCLUSIVE | LK_RETRY);
 	error = mac_system_check_swapoff(cred, sp->sw_vp);
@@ -2276,10 +2267,7 @@ swapoff_all(void)
 	const char *devname;
 	int error;
 
-	mtx_lock(&Giant);
-	while (swdev_syscall_active)
-		tsleep(&swdev_syscall_active, PUSER - 1, "swpoff", 0);
-	swdev_syscall_active = 1;
+	sx_xlock(&swdev_syscall_lock);
 
 	mtx_lock(&sw_dev_mtx);
 	TAILQ_FOREACH_SAFE(sp, &swtailq, sw_list, spt) {
@@ -2299,9 +2287,7 @@ swapoff_all(void)
 	}
 	mtx_unlock(&sw_dev_mtx);
 
-	swdev_syscall_active = 0;
-	wakeup_one(&swdev_syscall_active);
-	mtx_unlock(&Giant);
+	sx_xunlock(&swdev_syscall_lock);
 }
 
 void

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