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vfs: manage mnt_lockref with atomics

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See r352424.

Reviewed by:	kib, jeff
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D21574
This commit is contained in:
Mateusz Guzik 2019-09-16 21:32:21 +00:00
parent a8c8e44bf0
commit ee831b2543
1 changed files with 27 additions and 4 deletions
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31
sys/kern/vfs_subr.c
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@ -641,6 +641,18 @@ vfs_busy(struct mount *mp, int flags)
MPASS((flags & ~MBF_MASK) == 0);
CTR3(KTR_VFS, "%s: mp %p with flags %d", __func__, mp, flags);
if (vfs_op_thread_enter(mp)) {
MPASS((mp->mnt_kern_flag & MNTK_DRAINING) == 0);
MPASS((mp->mnt_kern_flag & MNTK_UNMOUNT) == 0);
MPASS((mp->mnt_kern_flag & MNTK_REFEXPIRE) == 0);
MNT_REF_UNLOCKED(mp);
atomic_add_int(&mp->mnt_lockref, 1);
vfs_op_thread_exit(mp);
if (flags & MBF_MNTLSTLOCK)
mtx_unlock(&mountlist_mtx);
return (0);
}
MNT_ILOCK(mp);
MNT_REF(mp);
/*
@ -673,7 +685,7 @@ vfs_busy(struct mount *mp, int flags)
}
if (flags & MBF_MNTLSTLOCK)
mtx_unlock(&mountlist_mtx);
mp->mnt_lockref++;
atomic_add_int(&mp->mnt_lockref, 1);
MNT_IUNLOCK(mp);
return (0);
}
@ -684,13 +696,24 @@ vfs_busy(struct mount *mp, int flags)
void
vfs_unbusy(struct mount *mp)
{
int c;
CTR2(KTR_VFS, "%s: mp %p", __func__, mp);
if (vfs_op_thread_enter(mp)) {
MPASS((mp->mnt_kern_flag & MNTK_DRAINING) == 0);
c = atomic_fetchadd_int(&mp->mnt_lockref, -1) - 1;
KASSERT(c >= 0, ("%s: negative mnt_lockref %d\n", __func__, c));
MNT_REL_UNLOCKED(mp);
vfs_op_thread_exit(mp);
return;
}
MNT_ILOCK(mp);
MNT_REL(mp);
KASSERT(mp->mnt_lockref > 0, ("negative mnt_lockref"));
mp->mnt_lockref--;
if (mp->mnt_lockref == 0 && (mp->mnt_kern_flag & MNTK_DRAINING) != 0) {
c = atomic_fetchadd_int(&mp->mnt_lockref, -1) - 1;
KASSERT(c >= 0, ("%s: negative mnt_lockref %d\n", __func__, c));
if (c == 0 && (mp->mnt_kern_flag & MNTK_DRAINING) != 0) {
MPASS(mp->mnt_kern_flag & MNTK_UNMOUNT);
CTR1(KTR_VFS, "%s: waking up waiters", __func__);
mp->mnt_kern_flag &= ~MNTK_DRAINING;