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devfs: rework si_usecount to track opens

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This removes a lot of special casing from the VFS layer.

Reviewed by:	kib (previous version)
Tested by:	pho (previous version)
Differential Revision:	https://reviews.freebsd.org/D25612
This commit is contained in:
Mateusz Guzik 2020-08-11 14:27:57 +00:00
parent 8bc30d2afd
commit 3b44443626
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=364113
7 changed files with 159 additions and 211 deletions
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5
sys/fs/devfs/devfs.h
View File

@ -153,6 +153,7 @@ struct devfs_dirent {
struct timespec de_ctime;
struct vnode *de_vnode;
char *de_symlink;
int de_usecount;
};
struct devfs_mount {
@ -203,6 +204,10 @@ struct devfs_dirent *devfs_vmkdir(struct devfs_mount *, char *, int,
struct devfs_dirent *devfs_find(struct devfs_dirent *, const char *, int,
int);
void devfs_ctty_ref(struct vnode *);
void devfs_ctty_unref(struct vnode *);
int devfs_usecount(struct vnode *);
#endif /* _KERNEL */
#endif /* !_FS_DEVFS_DEVFS_H_ */

162
sys/fs/devfs/devfs_vnops.c
View File

@ -222,6 +222,115 @@ devfs_clear_cdevpriv(void)
devfs_fpdrop(fp);
}
static void
devfs_usecount_add(struct vnode *vp)
{
struct devfs_dirent *de;
struct cdev *dev;
mtx_lock(&devfs_de_interlock);
VI_LOCK(vp);
VNPASS(vp->v_type == VCHR || vp->v_type == VBAD, vp);
if (VN_IS_DOOMED(vp)) {
goto out_unlock;
}
de = vp->v_data;
dev = vp->v_rdev;
MPASS(de != NULL);
MPASS(dev != NULL);
dev->si_usecount++;
de->de_usecount++;
out_unlock:
VI_UNLOCK(vp);
mtx_unlock(&devfs_de_interlock);
}
static void
devfs_usecount_subl(struct vnode *vp)
{
struct devfs_dirent *de;
struct cdev *dev;
mtx_assert(&devfs_de_interlock, MA_OWNED);
ASSERT_VI_LOCKED(vp, __func__);
VNPASS(vp->v_type == VCHR || vp->v_type == VBAD, vp);
de = vp->v_data;
dev = vp->v_rdev;
if (de == NULL)
return;
if (dev == NULL) {
MPASS(de->de_usecount == 0);
return;
}
if (dev->si_usecount < de->de_usecount)
panic("%s: si_usecount underflow for dev %p "
"(has %ld, dirent has %d)\n",
__func__, dev, dev->si_usecount, de->de_usecount);
if (VN_IS_DOOMED(vp)) {
dev->si_usecount -= de->de_usecount;
de->de_usecount = 0;
} else {
if (de->de_usecount == 0)
panic("%s: de_usecount underflow for dev %p\n",
__func__, dev);
dev->si_usecount--;
de->de_usecount--;
}
}
static void
devfs_usecount_sub(struct vnode *vp)
{
mtx_lock(&devfs_de_interlock);
VI_LOCK(vp);
devfs_usecount_subl(vp);
VI_UNLOCK(vp);
mtx_unlock(&devfs_de_interlock);
}
static int
devfs_usecountl(struct vnode *vp)
{
VNPASS(vp->v_type == VCHR, vp);
mtx_assert(&devfs_de_interlock, MA_OWNED);
ASSERT_VI_LOCKED(vp, __func__);
return (vp->v_rdev->si_usecount);
}
int
devfs_usecount(struct vnode *vp)
{
int count;
VNPASS(vp->v_type == VCHR, vp);
mtx_lock(&devfs_de_interlock);
VI_LOCK(vp);
count = devfs_usecountl(vp);
VI_UNLOCK(vp);
mtx_unlock(&devfs_de_interlock);
return (count);
}
void
devfs_ctty_ref(struct vnode *vp)
{
vrefact(vp);
devfs_usecount_add(vp);
}
void
devfs_ctty_unref(struct vnode *vp)
{
devfs_usecount_sub(vp);
vrele(vp);
}
/*
* On success devfs_populate_vp() returns with dmp->dm_lock held.
*/
@ -487,7 +596,6 @@ devfs_allocv(struct devfs_dirent *de, struct mount *mp, int lockmode,
/* XXX: v_rdev should be protect by vnode lock */
vp->v_rdev = dev;
VNPASS(vp->v_usecount == 1, vp);
dev->si_usecount++;
/* Special casing of ttys for deadfs. Probably redundant. */
dsw = dev->si_devsw;
if (dsw != NULL && (dsw->d_flags & D_TTY) != 0)
@ -569,6 +677,7 @@ devfs_close(struct vop_close_args *ap)
struct proc *p;
struct cdev *dev = vp->v_rdev;
struct cdevsw *dsw;
struct devfs_dirent *de = vp->v_data;
int dflags, error, ref, vp_locked;
/*
@ -587,7 +696,7 @@ devfs_close(struct vop_close_args *ap)
* if the reference count is 2 (this last descriptor
* plus the session), release the reference from the session.
*/
if (vp->v_usecount == 2 && td != NULL) {
if (de->de_usecount == 2 && td != NULL) {
p = td->td_proc;
PROC_LOCK(p);
if (vp == p->p_session->s_ttyvp) {
@ -596,19 +705,20 @@ devfs_close(struct vop_close_args *ap)
sx_xlock(&proctree_lock);
if (vp == p->p_session->s_ttyvp) {
SESS_LOCK(p->p_session);
mtx_lock(&devfs_de_interlock);
VI_LOCK(vp);
if (vp->v_usecount == 2 && vcount(vp) == 1 &&
!VN_IS_DOOMED(vp)) {
if (devfs_usecountl(vp) == 2 && !VN_IS_DOOMED(vp)) {
p->p_session->s_ttyvp = NULL;
p->p_session->s_ttydp = NULL;
oldvp = vp;
}
VI_UNLOCK(vp);
mtx_unlock(&devfs_de_interlock);
SESS_UNLOCK(p->p_session);
}
sx_xunlock(&proctree_lock);
if (oldvp != NULL)
vrele(oldvp);
devfs_ctty_unref(oldvp);
} else
PROC_UNLOCK(p);
}
@ -625,9 +735,12 @@ devfs_close(struct vop_close_args *ap)
if (dsw == NULL)
return (ENXIO);
dflags = 0;
mtx_lock(&devfs_de_interlock);
VI_LOCK(vp);
if (vp->v_usecount == 1 && vcount(vp) == 1)
if (devfs_usecountl(vp) == 1)
dflags |= FLASTCLOSE;
devfs_usecount_subl(vp);
mtx_unlock(&devfs_de_interlock);
if (VN_IS_DOOMED(vp)) {
/* Forced close. */
dflags |= FREVOKE | FNONBLOCK;
@ -850,7 +963,7 @@ devfs_ioctl(struct vop_ioctl_args *ap)
return (0);
}
vrefact(vp);
devfs_ctty_ref(vp);
SESS_LOCK(sess);
vpold = sess->s_ttyvp;
sess->s_ttyvp = vp;
@ -1159,6 +1272,9 @@ devfs_open(struct vop_open_args *ap)
return (ENXIO);
}
if (vp->v_type == VCHR)
devfs_usecount_add(vp);
vlocked = VOP_ISLOCKED(vp);
VOP_UNLOCK(vp);
@ -1178,6 +1294,9 @@ devfs_open(struct vop_open_args *ap)
td->td_fpop = fpop;
vn_lock(vp, vlocked | LK_RETRY);
if (error != 0 && vp->v_type == VCHR)
devfs_usecount_sub(vp);
dev_relthread(dev, ref);
if (error != 0) {
if (error == ERESTART)
@ -1406,19 +1525,28 @@ devfs_readlink(struct vop_readlink_args *ap)
return (uiomove(de->de_symlink, strlen(de->de_symlink), ap->a_uio));
}
static void
devfs_reclaiml(struct vnode *vp)
{
struct devfs_dirent *de;
mtx_assert(&devfs_de_interlock, MA_OWNED);
de = vp->v_data;
if (de != NULL) {
MPASS(de->de_usecount == 0);
de->de_vnode = NULL;
vp->v_data = NULL;
}
}
static int
devfs_reclaim(struct vop_reclaim_args *ap)
{
struct vnode *vp;
struct devfs_dirent *de;
vp = ap->a_vp;
mtx_lock(&devfs_de_interlock);
de = vp->v_data;
if (de != NULL) {
de->de_vnode = NULL;
vp->v_data = NULL;
}
devfs_reclaiml(vp);
mtx_unlock(&devfs_de_interlock);
return (0);
}
@ -1432,14 +1560,14 @@ devfs_reclaim_vchr(struct vop_reclaim_args *ap)
vp = ap->a_vp;
MPASS(vp->v_type == VCHR);
devfs_reclaim(ap);
mtx_lock(&devfs_de_interlock);
VI_LOCK(vp);
devfs_usecount_subl(vp);
devfs_reclaiml(vp);
mtx_unlock(&devfs_de_interlock);
dev_lock();
dev = vp->v_rdev;
vp->v_rdev = NULL;
if (dev != NULL)
dev->si_usecount -= (vp->v_usecount > 0);
dev_unlock();
VI_UNLOCK(vp);
if (dev != NULL)

4
sys/kern/kern_proc.c
View File

@ -88,6 +88,8 @@ __FBSDID("$FreeBSD$");
#include <vm/vm_page.h>
#include <vm/uma.h>
#include <fs/devfs/devfs.h>
#ifdef COMPAT_FREEBSD32
#include <compat/freebsd32/freebsd32.h>
#include <compat/freebsd32/freebsd32_util.h>
@ -858,7 +860,7 @@ killjobc(void)
VOP_REVOKE(ttyvp, REVOKEALL);
VOP_UNLOCK(ttyvp);
}
vrele(ttyvp);
devfs_ctty_unref(ttyvp);
sx_xlock(&proctree_lock);
}
}

4
sys/kern/tty.c
View File

@ -67,6 +67,8 @@ __FBSDID("$FreeBSD$");
#include <sys/ucred.h>
#include <sys/vnode.h>
#include <fs/devfs/devfs.h>
#include <machine/stdarg.h>
static MALLOC_DEFINE(M_TTY, "tty", "tty device");
@ -1256,7 +1258,7 @@ tty_drop_ctty(struct tty *tp, struct proc *p)
* is either changed or released.
*/
if (vp != NULL)
vrele(vp);
devfs_ctty_unref(vp);
return (0);
}

190
sys/kern/vfs_subr.c
View File

@ -108,8 +108,6 @@ static int flushbuflist(struct bufv *bufv, int flags, struct bufobj *bo,
static void syncer_shutdown(void *arg, int howto);
static int vtryrecycle(struct vnode *vp);
static void v_init_counters(struct vnode *);
static void v_incr_devcount(struct vnode *);
static void v_decr_devcount(struct vnode *);
static void vgonel(struct vnode *);
static void vfs_knllock(void *arg);
static void vfs_knlunlock(void *arg);
@ -2793,59 +2791,6 @@ v_init_counters(struct vnode *vp)
refcount_init(&vp->v_usecount, 1);
}
/*
* Increment si_usecount of the associated device, if any.
*/
static void
v_incr_devcount(struct vnode *vp)
{
ASSERT_VI_LOCKED(vp, __FUNCTION__);
if (vp->v_type == VCHR && vp->v_rdev != NULL) {
dev_lock();
vp->v_rdev->si_usecount++;
dev_unlock();
}
}
/*
* Decrement si_usecount of the associated device, if any.
*
* The caller is required to hold the interlock when transitioning a VCHR use
* count to zero. This prevents a race with devfs_reclaim_vchr() that would
* leak a si_usecount reference. The vnode lock will also prevent this race
* if it is held while dropping the last ref.
*
* The race is:
*
* CPU1 CPU2
* devfs_reclaim_vchr
* make v_usecount == 0
* VI_LOCK
* sees v_usecount == 0, no updates
* vp->v_rdev = NULL;
* ...
* VI_UNLOCK
* VI_LOCK
* v_decr_devcount
* sees v_rdev == NULL, no updates
*
* In this scenario si_devcount decrement is not performed.
*/
static void
v_decr_devcount(struct vnode *vp)
{
ASSERT_VOP_LOCKED(vp, __func__);
ASSERT_VI_LOCKED(vp, __FUNCTION__);
if (vp->v_type == VCHR && vp->v_rdev != NULL) {
dev_lock();
VNPASS(vp->v_rdev->si_usecount > 0, vp);
vp->v_rdev->si_usecount--;
dev_unlock();
}
}
/*
* Grab a particular vnode from the free list, increment its
* reference count and lock it. VIRF_DOOMED is set if the vnode
@ -2921,41 +2866,6 @@ vget(struct vnode *vp, int flags, struct thread *td)
return (vget_finish(vp, flags, vs));
}
static void __noinline
vget_finish_vchr(struct vnode *vp)
{
VNASSERT(vp->v_type == VCHR, vp, ("type != VCHR)"));
/*
* See the comment in vget_finish before usecount bump.
*/
if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
#ifdef INVARIANTS
int old = atomic_fetchadd_int(&vp->v_holdcnt, -1);
VNASSERT(old > 0, vp, ("%s: wrong hold count %d", __func__, old));
#else
refcount_release(&vp->v_holdcnt);
#endif
return;
}
VI_LOCK(vp);
if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
#ifdef INVARIANTS
int old = atomic_fetchadd_int(&vp->v_holdcnt, -1);
VNASSERT(old > 1, vp, ("%s: wrong hold count %d", __func__, old));
#else
refcount_release(&vp->v_holdcnt);
#endif
VI_UNLOCK(vp);
return;
}
v_incr_devcount(vp);
refcount_acquire(&vp->v_usecount);
VI_UNLOCK(vp);
}
int
vget_finish(struct vnode *vp, int flags, enum vgetstate vs)
{
@ -2993,11 +2903,6 @@ vget_finish_ref(struct vnode *vp, enum vgetstate vs)
if (vs == VGET_USECOUNT)
return;
if (__predict_false(vp->v_type == VCHR)) {
vget_finish_vchr(vp);
return;
}
/*
* We hold the vnode. If the usecount is 0 it will be utilized to keep
* the vnode around. Otherwise someone else lended their hold count and
@ -3019,61 +2924,12 @@ vget_finish_ref(struct vnode *vp, enum vgetstate vs)
* Increase the reference (use) and hold count of a vnode.
* This will also remove the vnode from the free list if it is presently free.
*/
static void __noinline
vref_vchr(struct vnode *vp, bool interlock)
{
/*
* See the comment in vget_finish before usecount bump.
*/
if (!interlock) {
if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
VNODE_REFCOUNT_FENCE_ACQ();
VNASSERT(vp->v_holdcnt > 0, vp,
("%s: active vnode not held", __func__));
return;
}
VI_LOCK(vp);
/*
* By the time we get here the vnode might have been doomed, at
* which point the 0->1 use count transition is no longer
* protected by the interlock. Since it can't bounce back to
* VCHR and requires vref semantics, punt it back
*/
if (__predict_false(vp->v_type == VBAD)) {
VI_UNLOCK(vp);
vref(vp);
return;
}
}
VNASSERT(vp->v_type == VCHR, vp, ("type != VCHR)"));
if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
VNODE_REFCOUNT_FENCE_ACQ();
VNASSERT(vp->v_holdcnt > 0, vp,
("%s: active vnode not held", __func__));
if (!interlock)
VI_UNLOCK(vp);
return;
}
vhold(vp);
v_incr_devcount(vp);
refcount_acquire(&vp->v_usecount);
if (!interlock)
VI_UNLOCK(vp);
return;
}
void
vref(struct vnode *vp)
{
int old;
CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
if (__predict_false(vp->v_type == VCHR)) {
vref_vchr(vp, false);
return;
}
if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
VNODE_REFCOUNT_FENCE_ACQ();
VNASSERT(vp->v_holdcnt > 0, vp,
@ -3102,10 +2958,6 @@ vrefl(struct vnode *vp)
ASSERT_VI_LOCKED(vp, __func__);
CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
if (__predict_false(vp->v_type == VCHR)) {
vref_vchr(vp, true);
return;
}
vref(vp);
}
@ -3246,9 +3098,6 @@ enum vput_op { VRELE, VPUT, VUNREF };
* By releasing the last usecount we take ownership of the hold count which
* provides liveness of the vnode, meaning we have to vdrop.
*
* If the vnode is of type VCHR we may need to decrement si_usecount, see
* v_decr_devcount for details.
*
* For all vnodes we may need to perform inactive processing. It requires an
* exclusive lock on the vnode, while it is legal to call here with only a
* shared lock (or no locks). If locking the vnode in an expected manner fails,
@ -3269,8 +3118,6 @@ vput_final(struct vnode *vp, enum vput_op func)
VNPASS(vp->v_holdcnt > 0, vp);
VI_LOCK(vp);
if (__predict_false(vp->v_type == VCHR && func != VRELE))
v_decr_devcount(vp);
/*
* By the time we got here someone else might have transitioned
@ -3358,28 +3205,9 @@ vput_final(struct vnode *vp, enum vput_op func)
* Releasing the last use count requires additional processing, see vput_final
* above for details.
*
* Note that releasing use count without the vnode lock requires special casing
* for VCHR, see v_decr_devcount for details.
*
* Comment above each variant denotes lock state on entry and exit.
*/
static void __noinline
vrele_vchr(struct vnode *vp)
{
if (refcount_release_if_not_last(&vp->v_usecount))
return;
VI_LOCK(vp);
if (!refcount_release(&vp->v_usecount)) {
VI_UNLOCK(vp);
return;
}
v_decr_devcount(vp);
VI_UNLOCK(vp);
vput_final(vp, VRELE);
}
/*
* in: any
* out: same as passed in
@ -3389,10 +3217,6 @@ vrele(struct vnode *vp)
{
ASSERT_VI_UNLOCKED(vp, __func__);
if (__predict_false(vp->v_type == VCHR)) {
vrele_vchr(vp);
return;
}
if (!refcount_release(&vp->v_usecount))
return;
vput_final(vp, VRELE);
@ -4143,20 +3967,6 @@ vgonel(struct vnode *vp)
vp->v_type = VBAD;
}
/*
* Calculate the total number of references to a special device.
*/
int
vcount(struct vnode *vp)
{
int count;
dev_lock();
count = vp->v_rdev->si_usecount;
dev_unlock();
return (count);
}
/*
* Print out a description of a vnode.
*/

4
sys/kern/vfs_syscalls.c
View File

@ -87,6 +87,8 @@ __FBSDID("$FreeBSD$");
#include <vm/vm_page.h>
#include <vm/uma.h>
#include <fs/devfs/devfs.h>
#include <ufs/ufs/quota.h>
MALLOC_DEFINE(M_FADVISE, "fadvise", "posix_fadvise(2) information");
@ -4213,7 +4215,7 @@ sys_revoke(struct thread *td, struct revoke_args *uap)
if (error != 0)
goto out;
}
if (vp->v_usecount > 1 || vcount(vp) > 1)
if (devfs_usecount(vp) > 0)
VOP_REVOKE(vp, REVOKEALL);
out:
vput(vp);

1
sys/sys/vnode.h
View File

@ -676,7 +676,6 @@ int vaccess_acl_posix1e(enum vtype type, uid_t file_uid,
gid_t file_gid, struct acl *acl, accmode_t accmode,
struct ucred *cred);
void vattr_null(struct vattr *vap);
int vcount(struct vnode *vp);
void vlazy(struct vnode *);
void vdrop(struct vnode *);
void vdropl(struct vnode *);