vfs: manage mnt_writeopcount with atomics

See r352424.

Reviewed by:	kib, jeff
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D21575

diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index 1263f0c677a75555188db636eed2f114bf3753c8..7cccc2914f9f76bc154fb613a13702bc6a3c4087 100644 (file)
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -1621,11 +1621,23 @@ vn_suspendable(struct mount *mp)
  * suspension is over, and then proceed.
  */
 static int
-vn_start_write_locked(struct mount *mp, int flags)
+vn_start_write_refed(struct mount *mp, int flags, bool mplocked)
 {
        int error, mflags;
 
-       mtx_assert(MNT_MTX(mp), MA_OWNED);
+       if (__predict_true(!mplocked) && (flags & V_XSLEEP) == 0 &&
+           vfs_op_thread_enter(mp)) {
+               MPASS((mp->mnt_kern_flag & MNTK_SUSPEND) == 0);
+               atomic_add_int(&mp->mnt_writeopcount, 1);
+               vfs_op_thread_exit(mp);
+               return (0);
+       }
+
+       if (mplocked)
+               mtx_assert(MNT_MTX(mp), MA_OWNED);
+       else
+               MNT_ILOCK(mp);
+
        error = 0;
 
        /*
@@ -1648,7 +1660,7 @@ vn_start_write_locked(struct mount *mp, int flags)
        }
        if (flags & V_XSLEEP)
                goto unlock;
-       mp->mnt_writeopcount++;
+       atomic_add_int(&mp->mnt_writeopcount, 1);
 unlock:
        if (error != 0 || (flags & V_XSLEEP) != 0)
                MNT_REL(mp);
@@ -1694,11 +1706,10 @@ vn_start_write(struct vnode *vp, struct mount **mpp, int flags)
         * refcount for the provided mountpoint too, in order to
         * emulate a vfs_ref().
         */
-       MNT_ILOCK(mp);
        if (vp == NULL && (flags & V_MNTREF) == 0)
-               MNT_REF(mp);
+               vfs_ref(mp);
 
-       return (vn_start_write_locked(mp, flags));
+       return (vn_start_write_refed(mp, flags, false));
 }
 
 /*
@@ -1780,15 +1791,26 @@ vn_start_secondary_write(struct vnode *vp, struct mount **mpp, int flags)
 void
 vn_finished_write(struct mount *mp)
 {
+       int c;
+
        if (mp == NULL || !vn_suspendable(mp))
                return;
+
+       if (vfs_op_thread_enter(mp)) {
+               c = atomic_fetchadd_int(&mp->mnt_writeopcount, -1) - 1;
+               if (c < 0)
+                       panic("vn_finished_write: invalid writeopcount %d", c);
+               MNT_REL_UNLOCKED(mp);
+               vfs_op_thread_exit(mp);
+               return;
+       }
+
        MNT_ILOCK(mp);
        MNT_REL(mp);
-       mp->mnt_writeopcount--;
-       if (mp->mnt_writeopcount < 0)
-               panic("vn_finished_write: neg cnt");
-       if ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0 &&
-           mp->mnt_writeopcount <= 0)
+       c = atomic_fetchadd_int(&mp->mnt_writeopcount, -1) - 1;
+       if (c < 0)
+               panic("vn_finished_write: invalid writeopcount %d", c);
+       if ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0 && c == 0)
                wakeup(&mp->mnt_writeopcount);
        MNT_IUNLOCK(mp);
 }
@@ -1827,8 +1849,11 @@ vfs_write_suspend(struct mount *mp, int flags)
 
        MPASS(vn_suspendable(mp));
 
+       vfs_op_enter(mp);
+
        MNT_ILOCK(mp);
        if (mp->mnt_susp_owner == curthread) {
+               vfs_op_exit_locked(mp);
                MNT_IUNLOCK(mp);
                return (EALREADY);
        }
@@ -1845,6 +1870,7 @@ vfs_write_suspend(struct mount *mp, int flags)
         */
        if ((flags & VS_SKIP_UNMOUNT) != 0 &&
            (mp->mnt_kern_flag & MNTK_UNMOUNT) != 0) {
+               vfs_op_exit_locked(mp);
                MNT_IUNLOCK(mp);
                return (EBUSY);
        }
@@ -1856,8 +1882,10 @@ vfs_write_suspend(struct mount *mp, int flags)
                    MNT_MTX(mp), (PUSER - 1)|PDROP, "suspwt", 0);
        else
                MNT_IUNLOCK(mp);
-       if ((error = VFS_SYNC(mp, MNT_SUSPEND)) != 0)
+       if ((error = VFS_SYNC(mp, MNT_SUSPEND)) != 0) {
                vfs_write_resume(mp, 0);
+               vfs_op_exit(mp);
+       }
        return (error);
 }
 
@@ -1881,14 +1909,15 @@ vfs_write_resume(struct mount *mp, int flags)
                curthread->td_pflags &= ~TDP_IGNSUSP;
                if ((flags & VR_START_WRITE) != 0) {
                        MNT_REF(mp);
-                       mp->mnt_writeopcount++;
+                       atomic_add_int(&mp->mnt_writeopcount, 1);
                }
                MNT_IUNLOCK(mp);
                if ((flags & VR_NO_SUSPCLR) == 0)
                        VFS_SUSP_CLEAN(mp);
+               vfs_op_exit(mp);
        } else if ((flags & VR_START_WRITE) != 0) {
                MNT_REF(mp);
-               vn_start_write_locked(mp, 0);
+               vn_start_write_refed(mp, 0, true);
        } else {
                MNT_IUNLOCK(mp);
        }

diff --git a/sys/ufs/ffs/ffs_softdep.c b/sys/ufs/ffs/ffs_softdep.c
index 061b73f9c106d20246f5ee23fafd0da4a5662720..d9f07f3d993098f8ffb446e0a0aab0a23ad1a1cc 100644 (file)
--- a/sys/ufs/ffs/ffs_softdep.c
+++ b/sys/ufs/ffs/ffs_softdep.c
@@ -2954,17 +2954,26 @@ journal_suspend(ump)
 {
        struct jblocks *jblocks;
        struct mount *mp;
+       bool set;
 
        mp = UFSTOVFS(ump);
+       if ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0)
+               return;
+
        jblocks = ump->softdep_jblocks;
+       vfs_op_enter(mp);
+       set = false;
        MNT_ILOCK(mp);
        if ((mp->mnt_kern_flag & MNTK_SUSPEND) == 0) {
                stat_journal_min++;
                mp->mnt_kern_flag |= MNTK_SUSPEND;
                mp->mnt_susp_owner = ump->softdep_flushtd;
+               set = true;
        }
        jblocks->jb_suspended = 1;
        MNT_IUNLOCK(mp);
+       if (!set)
+               vfs_op_exit(mp);
 }
 
 static int