Author: mjg
Date: Tue Aug 4 23:04:29 2020
New Revision: 363872
URL: https://svnweb.freebsd.org/changeset/base/363872
Log:
cache: add cache_purge_vgone
cache_purge locklessly checks whether the vnode at hand has any namecache
entries. This can race with a concurrent purge which managed to remove
the last entry, but may not be done touching the vnode.
Make sure we observe the relevant vnode lock as not taken before proceeding
with vgone.
Paired with the fact that doomed vnodes cannnot receive entries this restores
the invariant that there are no namecache-related writing users past
cache_purge
in vgone.
Reported by: pho
Modified:
head/sys/kern/vfs_cache.c
head/sys/kern/vfs_subr.c
head/sys/sys/vnode.h
Modified: head/sys/kern/vfs_cache.c
==============================================================================
--- head/sys/kern/vfs_cache.c Tue Aug 4 23:00:00 2020 (r363871)
+++ head/sys/kern/vfs_cache.c Tue Aug 4 23:04:29 2020 (r363872)
@@ -2138,22 +2138,17 @@ cache_changesize(u_long newmaxvnodes)
/*
* Invalidate all entries from and to a particular vnode.
*/
-void
-cache_purge(struct vnode *vp)
+static void
+cache_purge_impl(struct vnode *vp)
{
TAILQ_HEAD(, namecache) ncps;
struct namecache *ncp, *nnp;
struct mtx *vlp, *vlp2;
- CTR1(KTR_VFS, "cache_purge(%p)", vp);
- SDT_PROBE1(vfs, namecache, purge, done, vp);
- if (LIST_EMPTY(&vp->v_cache_src) && TAILQ_EMPTY(&vp->v_cache_dst) &&
- vp->v_cache_dd == NULL)
- return;
TAILQ_INIT(&ncps);
vlp = VP2VNODELOCK(vp);
vlp2 = NULL;
- mtx_lock(vlp);
+ mtx_assert(vlp, MA_OWNED);
retry:
while (!LIST_EMPTY(&vp->v_cache_src)) {
ncp = LIST_FIRST(&vp->v_cache_src);
@@ -2182,6 +2177,53 @@ retry:
TAILQ_FOREACH_SAFE(ncp, &ncps, nc_dst, nnp) {
cache_free(ncp);
}
+}
+
+void
+cache_purge(struct vnode *vp)
+{
+ struct mtx *vlp;
+
+ SDT_PROBE1(vfs, namecache, purge, done, vp);
+ if (LIST_EMPTY(&vp->v_cache_src) && TAILQ_EMPTY(&vp->v_cache_dst) &&
+ vp->v_cache_dd == NULL)
+ return;
+ vlp = VP2VNODELOCK(vp);
+ mtx_lock(vlp);
+ cache_purge_impl(vp);
+}
+
+/*
+ * Only to be used by vgone.
+ */
+void
+cache_purge_vgone(struct vnode *vp)
+{
+ struct mtx *vlp;
+
+ VNPASS(VN_IS_DOOMED(vp), vp);
+ vlp = VP2VNODELOCK(vp);
+ if (!(LIST_EMPTY(&vp->v_cache_src) && TAILQ_EMPTY(&vp->v_cache_dst) &&
+ vp->v_cache_dd == NULL)) {
+ mtx_lock(vlp);
+ cache_purge_impl(vp);
+ mtx_assert(vlp, MA_NOTOWNED);
+ return;
+ }
+
+ /*
+ * All the NULL pointer state we found above may be transient.
+ * Serialize against a possible thread doing cache_purge.
+ */
+ mtx_wait_unlocked(vlp);
+ if (!(LIST_EMPTY(&vp->v_cache_src) && TAILQ_EMPTY(&vp->v_cache_dst) &&
+ vp->v_cache_dd == NULL)) {
+ mtx_lock(vlp);
+ cache_purge_impl(vp);
+ mtx_assert(vlp, MA_NOTOWNED);
+ return;
+ }
+ return;
}
/*
Modified: head/sys/kern/vfs_subr.c
==============================================================================
--- head/sys/kern/vfs_subr.c Tue Aug 4 23:00:00 2020 (r363871)
+++ head/sys/kern/vfs_subr.c Tue Aug 4 23:04:29 2020 (r363872)
@@ -4146,7 +4146,7 @@ vgonel(struct vnode *vp)
* Delete from old mount point vnode list.
*/
delmntque(vp);
- cache_purge(vp);
+ cache_purge_vgone(vp);
/*
* Done with purge, reset to the standard lock and invalidate
* the vnode.
Modified: head/sys/sys/vnode.h
==============================================================================
--- head/sys/sys/vnode.h Tue Aug 4 23:00:00 2020 (r363871)
+++ head/sys/sys/vnode.h Tue Aug 4 23:04:29 2020 (r363872)
@@ -638,6 +638,7 @@ int cache_lookup(struct vnode *dvp, struct vnode **vpp
struct componentname *cnp, struct timespec *tsp, int *ticksp);
void cache_vnode_init(struct vnode *vp);
void cache_purge(struct vnode *vp);
+void cache_purge_vgone(struct vnode *vp);
void cache_purge_negative(struct vnode *vp);
void cache_purgevfs(struct mount *mp, bool force);
int change_dir(struct vnode *vp, struct thread *td);
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