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null_vput_pair(): release use reference on dvp earlier

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We might own the last use reference, and then vrele() at the end would
need to take the dvp vnode lock to inactivate, which causes deadlock
with vp. We cannot vrele() dvp from start since this might unlock ldvp.

Handle it by holding the vnode and dropping use ref after lowerfs
VOP_VPUT_PAIR() ended.  This effectivaly requires unlock of the vp vnode
after VOP_VPUT_PAIR(), so the call is changed to set unlock_vp to true
unconditionally.  This opens more opportunities for vp to be reclaimed,
if lvp is still alive we reinstantiate vp with null_nodeget().

Reported and tested by:	pho
Reviewed by:	mckusick
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D29178
This commit is contained in:
Konstantin Belousov 2021-03-07 23:08:38 +02:00
parent 44691b33cc
commit 16dea83410
1 changed files with 31 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
sys/fs/nullfs/null_vnops.c
View File

@ -985,33 +985,50 @@ null_vput_pair(struct vop_vput_pair_args *ap)
vpp = ap->a_vpp;
vp = NULL;
lvp = NULL;
if (vpp != NULL) {
mp = NULL;
if (vpp != NULL)
vp = *vpp;
if (vp != NULL) {
if (vp != NULL) {
lvp = NULLVPTOLOWERVP(vp);
vref(lvp);
if (!ap->a_unlock_vp) {
vhold(vp);
vhold(lvp);
mp = vp->v_mount;
lvp = NULLVPTOLOWERVP(vp);
if (ap->a_unlock_vp)
vref(lvp);
vfs_ref(mp);
}
}
res = VOP_VPUT_PAIR(ldvp, &lvp, ap->a_unlock_vp);
res = VOP_VPUT_PAIR(ldvp, lvp != NULL ? &lvp : NULL, true);
if (vp != NULL && ap->a_unlock_vp)
vrele(vp);
vrele(dvp);
/* lvp might have been unlocked and vp reclaimed */
if (vp != NULL) {
if (!ap->a_unlock_vp && vp->v_vnlock != lvp->v_vnlock) {
if (vp == NULL || ap->a_unlock_vp)
return (res);
/* lvp has been unlocked and vp might be reclaimed */
VOP_LOCK(vp, LK_EXCLUSIVE | LK_RETRY);
if (vp->v_data == NULL && vfs_busy(mp, MBF_NOWAIT) == 0) {
vput(vp);
vget(lvp, LK_EXCLUSIVE | LK_RETRY);
if (VN_IS_DOOMED(lvp)) {
vput(lvp);
vget(vp, LK_EXCLUSIVE | LK_RETRY);
} else {
error = null_nodeget(mp, lvp, &vp1);
if (error == 0) {
vput(vp);
*vpp = vp1;
} else {
vget(vp, LK_EXCLUSIVE | LK_RETRY);
}
}
if (ap->a_unlock_vp)
vrele(vp);
vdrop(vp);
vfs_unbusy(mp);
}
vrele(dvp);
vdrop(lvp);
vdrop(vp);
vfs_rel(mp);
return (res);
}