Author: mjg
Date: Sat Oct 24 13:30:37 2020
New Revision: 366997
URL: https://svnweb.freebsd.org/changeset/base/366997
Log:
vfs: fix a race where reclaim vholds freed vnodes
Reported by: pho
Tested by: pho (previous version)
Fixes: r366974 ("vfs: stop taking the interlock in vnode reclaim")
Modified:
head/sys/kern/vfs_subr.c
Modified: head/sys/kern/vfs_subr.c
==============================================================================
--- head/sys/kern/vfs_subr.c Sat Oct 24 13:16:10 2020 (r366996)
+++ head/sys/kern/vfs_subr.c Sat Oct 24 13:30:37 2020 (r366997)
@@ -109,6 +109,7 @@ static void syncer_shutdown(void *arg, int howto);
static int vtryrecycle(struct vnode *vp);
static void v_init_counters(struct vnode *);
static void vgonel(struct vnode *);
+static bool vhold_recycle(struct vnode *);
static void vfs_knllock(void *arg);
static void vfs_knlunlock(void *arg);
static void vfs_knl_assert_locked(void *arg);
@@ -1126,7 +1127,8 @@ restart:
goto next_iter;
}
- vhold(vp);
+ if (!vhold_recycle(vp))
+ goto next_iter;
TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
TAILQ_INSERT_AFTER(&vnode_list, vp, mvp, v_vnodelist);
mtx_unlock(&vnode_list_mtx);
@@ -1231,7 +1233,8 @@ restart:
if (__predict_false(vp->v_type == VBAD || vp->v_type == VNON)) {
continue;
}
- vhold(vp);
+ if (!vhold_recycle(vp))
+ continue;
count--;
mtx_unlock(&vnode_list_mtx);
vtryrecycle(vp);
@@ -3248,13 +3251,11 @@ vholdnz(struct vnode *vp)
* However, while this is more performant, it hinders debugging by eliminating
* the previously mentioned invariant.
*/
-bool
-vhold_smr(struct vnode *vp)
+static bool __always_inline
+_vhold_cond(struct vnode *vp)
{
int count;
- VFS_SMR_ASSERT_ENTERED();
-
count = atomic_load_int(&vp->v_holdcnt);
for (;;) {
if (count & VHOLD_NO_SMR) {
@@ -3270,6 +3271,28 @@ vhold_smr(struct vnode *vp)
return (true);
}
}
+}
+
+bool
+vhold_smr(struct vnode *vp)
+{
+
+ VFS_SMR_ASSERT_ENTERED();
+ return (_vhold_cond(vp));
+}
+
+/*
+ * Special case for vnode recycling.
+ *
+ * Vnodes are present on the global list until UMA takes them out.
+ * Attempts to recycle only need the relevant lock and have no use for SMR.
+ */
+static bool
+vhold_recycle(struct vnode *vp)
+{
+
+ mtx_assert(&vnode_list_mtx, MA_OWNED);
+ return (_vhold_cond(vp));
}
static void __noinline
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