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Resolve the devfs deadlock caused by LOR between devfs_mount->dm_lock and

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vnode lock in devfs_allocv. Do this by temporary dropping dm_lock around
vnode locking.

For safe operation, add hold counters for both devfs_mount and devfs_dirent,
and DE_DOOMED flag for devfs_dirent. The facilities allow to continue after
dropping of the dm_lock, by making sure that referenced memory does not
disappear.

Reviewed by:	tegge
Tested by:	kris
Approved by:	kan (mentor)
PR:		kern/102335
This commit is contained in:
Konstantin Belousov 2006-09-18 13:23:08 +00:00
parent 827293df54
commit e7f9b74438
4 changed files with 113 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
sys/fs/devfs/devfs.h
View File

@ -129,6 +129,8 @@ struct devfs_dirent {
#define DE_WHITEOUT 0x1
#define DE_DOT 0x2
#define DE_DOTDOT 0x4
#define DE_DOOMED 0x8
int de_holdcnt;
struct dirent *de_dirent;
TAILQ_ENTRY(devfs_dirent) de_list;
TAILQ_HEAD(, devfs_dirent) de_dlist;
@ -150,6 +152,7 @@ struct devfs_mount {
struct mount *dm_mount;
struct devfs_dirent *dm_rootdir;
unsigned dm_generation;
int dm_holdcnt;
struct sx dm_lock;
devfs_rsnum dm_ruleset;
};
@ -160,13 +163,21 @@ extern unsigned devfs_rule_depth;
#define VFSTODEVFS(mp) ((struct devfs_mount *)((mp)->mnt_data))
#define DEVFS_DE_HOLD(de) ((de)->de_holdcnt++)
#define DEVFS_DE_DROP(de) (--(de)->de_holdcnt == 0)
#define DEVFS_DMP_HOLD(dmp) ((dmp)->dm_holdcnt++)
#define DEVFS_DMP_DROP(dmp) (--(dmp)->dm_holdcnt == 0)
void devfs_rules_apply(struct devfs_mount *dm, struct devfs_dirent *de);
void devfs_rules_cleanup (struct devfs_mount *dm);
int devfs_rules_ioctl(struct devfs_mount *dm, u_long cmd, caddr_t data, struct thread *td);
int devfs_allocv (struct devfs_dirent *de, struct mount *mp, struct vnode **vpp, struct thread *td);
void devfs_delete(struct devfs_mount *dm, struct devfs_dirent *de);
void devfs_dirent_free(struct devfs_dirent *de);
void devfs_populate (struct devfs_mount *dm);
void devfs_cleanup (struct devfs_mount *dm);
void devfs_unmount_final(struct devfs_mount *mp);
struct devfs_dirent *devfs_newdirent (char *name, int namelen);
struct devfs_dirent *devfs_vmkdir (struct devfs_mount *, char *name, int namelen, struct devfs_dirent *dotdot, u_int inode);
struct devfs_dirent *devfs_find (struct devfs_dirent *dd, const char *name, int namelen);

13
sys/fs/devfs/devfs_devs.c
View File

@ -179,6 +179,7 @@ devfs_newdirent(char *name, int namelen)
vfs_timestamp(&de->de_ctime);
de->de_mtime = de->de_atime = de->de_ctime;
de->de_links = 1;
de->de_holdcnt = 1;
#ifdef MAC
mac_init_devfsdirent(de);
#endif
@ -229,10 +230,19 @@ devfs_vmkdir(struct devfs_mount *dmp, char *name, int namelen, struct devfs_dire
return (dd);
}
void
devfs_dirent_free(struct devfs_dirent *de)
{
free(de, M_DEVFS3);
}
void
devfs_delete(struct devfs_mount *dm, struct devfs_dirent *de)
{
KASSERT((de->de_flags & DE_DOOMED) == 0,
("devfs_delete doomed dirent"));
de->de_flags |= DE_DOOMED;
if (de->de_symlink) {
free(de->de_symlink, M_DEVFS);
de->de_symlink = NULL;
@ -251,7 +261,8 @@ devfs_delete(struct devfs_mount *dm, struct devfs_dirent *de)
free_unr(devfs_inos, de->de_inode);
de->de_inode = 0;
}
free(de, M_DEVFS3);
if (DEVFS_DE_DROP(de))
devfs_dirent_free(de);
}
/*

24
sys/fs/devfs/devfs_vfsops.c
View File

@ -77,6 +77,7 @@ devfs_mount(struct mount *mp, struct thread *td)
fmp = malloc(sizeof *fmp, M_DEVFS, M_WAITOK | M_ZERO);
fmp->dm_idx = alloc_unr(devfs_unr);
sx_init(&fmp->dm_lock, "devfsmount");
fmp->dm_holdcnt = 1;
mp->mnt_flag |= MNT_LOCAL;
mp->mnt_kern_flag |= MNTK_MPSAFE;
@ -104,14 +105,25 @@ devfs_mount(struct mount *mp, struct thread *td)
return (0);
}
void
devfs_unmount_final(struct devfs_mount *fmp)
{
sx_destroy(&fmp->dm_lock);
free(fmp, M_DEVFS);
}
static int
devfs_unmount(struct mount *mp, int mntflags, struct thread *td)
{
int error;
int flags = 0;
struct devfs_mount *fmp;
int hold;
u_int idx;
fmp = VFSTODEVFS(mp);
KASSERT(fmp->dm_mount != NULL,
("devfs_unmount unmounted devfs_mount"));
/* There is 1 extra root vnode reference from devfs_mount(). */
error = vflush(mp, 1, flags, td);
if (error)
@ -119,11 +131,14 @@ devfs_unmount(struct mount *mp, int mntflags, struct thread *td)
sx_xlock(&fmp->dm_lock);
devfs_cleanup(fmp);
devfs_rules_cleanup(fmp);
sx_xunlock(&fmp->dm_lock);
fmp->dm_mount = NULL;
hold = --fmp->dm_holdcnt;
mp->mnt_data = NULL;
sx_destroy(&fmp->dm_lock);
free_unr(devfs_unr, fmp->dm_idx);
free(fmp, M_DEVFS);
idx = fmp->dm_idx;
sx_xunlock(&fmp->dm_lock);
free_unr(devfs_unr, idx);
if (hold == 0)
devfs_unmount_final(fmp);
return 0;
}
@ -137,6 +152,7 @@ devfs_root(struct mount *mp, int flags, struct vnode **vpp, struct thread *td)
struct devfs_mount *dmp;
dmp = VFSTODEVFS(mp);
sx_xlock(&dmp->dm_lock);
error = devfs_allocv(dmp->dm_rootdir, mp, &vp, td);
if (error)
return (error);

81
sys/fs/devfs/devfs_vnops.c
View File

@ -125,36 +125,84 @@ devfs_fqpn(char *buf, struct vnode *dvp, struct componentname *cnp)
return (buf + i);
}
static int
devfs_allocv_drop_refs(int drop_dm_lock, struct devfs_mount *dmp,
struct devfs_dirent *de)
{
int not_found;
not_found = 0;
if (de->de_flags & DE_DOOMED)
not_found = 1;
if (DEVFS_DE_DROP(de)) {
KASSERT(not_found == 1, ("DEVFS de dropped but not doomed"));
devfs_dirent_free(de);
}
if (DEVFS_DMP_DROP(dmp)) {
KASSERT(not_found == 1,
("DEVFS mount struct freed before dirent"));
not_found = 2;
sx_xunlock(&dmp->dm_lock);
devfs_unmount_final(dmp);
}
if (not_found == 1 || drop_dm_lock)
sx_unlock(&dmp->dm_lock);
return (not_found);
}
/*
* devfs_allocv shall be entered with dmp->dm_lock held, and it drops
* it on return.
*/
int
devfs_allocv(struct devfs_dirent *de, struct mount *mp, struct vnode **vpp, struct thread *td)
{
int error;
struct vnode *vp;
struct cdev *dev;
struct devfs_mount *dmp;
KASSERT(td == curthread, ("devfs_allocv: td != curthread"));
loop:
dmp = VFSTODEVFS(mp);
if (de->de_flags & DE_DOOMED) {
sx_xunlock(&dmp->dm_lock);
return (ENOENT);
}
loop:
DEVFS_DE_HOLD(de);
DEVFS_DMP_HOLD(dmp);
mtx_lock(&devfs_de_interlock);
vp = de->de_vnode;
if (vp != NULL) {
VI_LOCK(vp);
mtx_unlock(&devfs_de_interlock);
if (vget(vp, LK_EXCLUSIVE | LK_INTERLOCK, td))
sx_xunlock(&dmp->dm_lock);
error = vget(vp, LK_EXCLUSIVE | LK_INTERLOCK, td);
sx_xlock(&dmp->dm_lock);
if (devfs_allocv_drop_refs(0, dmp, de)) {
if (error == 0)
vput(vp);
return (ENOENT);
}
else if (error)
goto loop;
sx_xunlock(&dmp->dm_lock);
*vpp = vp;
return (0);
}
mtx_unlock(&devfs_de_interlock);
if (de->de_dirent->d_type == DT_CHR) {
if (!(de->de_cdp->cdp_flags & CDP_ACTIVE))
if (!(de->de_cdp->cdp_flags & CDP_ACTIVE)) {
devfs_allocv_drop_refs(1, dmp, de);
return (ENOENT);
}
dev = &de->de_cdp->cdp_c;
} else {
dev = NULL;
}
error = getnewvnode("devfs", mp, &devfs_vnodeops, &vp);
if (error != 0) {
devfs_allocv_drop_refs(1, dmp, de);
printf("devfs_allocv: failed to allocate new vnode\n");
return (error);
}
@ -182,10 +230,17 @@ loop:
vp->v_data = de;
de->de_vnode = vp;
mtx_unlock(&devfs_de_interlock);
sx_xunlock(&dmp->dm_lock);
vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
sx_xlock(&dmp->dm_lock);
if (devfs_allocv_drop_refs(0, dmp, de)) {
vput(vp);
return (ENOENT);
}
#ifdef MAC
mac_associate_vnode_devfs(mp, de, vp);
#endif
sx_xunlock(&dmp->dm_lock);
*vpp = vp;
return (0);
}
@ -456,7 +511,7 @@ devfs_kqfilter_f(struct file *fp, struct knote *kn)
}
static int
devfs_lookupx(struct vop_lookup_args *ap)
devfs_lookupx(struct vop_lookup_args *ap, int *dm_unlock)
{
struct componentname *cnp;
struct vnode *dvp, **vpp;
@ -508,6 +563,7 @@ devfs_lookupx(struct vop_lookup_args *ap)
de = TAILQ_NEXT(de, de_list); /* ".." */
de = de->de_dir;
error = devfs_allocv(de, dvp->v_mount, vpp, td);
*dm_unlock = 0;
vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY, td);
return (error);
}
@ -565,6 +621,7 @@ devfs_lookupx(struct vop_lookup_args *ap)
}
}
error = devfs_allocv(de, dvp->v_mount, vpp, td);
*dm_unlock = 0;
return (error);
}
@ -573,11 +630,14 @@ devfs_lookup(struct vop_lookup_args *ap)
{
int j;
struct devfs_mount *dmp;
int dm_unlock;
dmp = VFSTODEVFS(ap->a_dvp->v_mount);
dm_unlock = 1;
sx_xlock(&dmp->dm_lock);
j = devfs_lookupx(ap);
sx_xunlock(&dmp->dm_lock);
j = devfs_lookupx(ap, &dm_unlock);
if (dm_unlock == 1)
sx_xunlock(&dmp->dm_lock);
return (j);
}
@ -599,7 +659,6 @@ devfs_mknod(struct vop_mknod_args *ap)
return (EOPNOTSUPP);
dvp = ap->a_dvp;
dmp = VFSTODEVFS(dvp->v_mount);
sx_xlock(&dmp->dm_lock);
cnp = ap->a_cnp;
vpp = ap->a_vpp;
@ -607,6 +666,7 @@ devfs_mknod(struct vop_mknod_args *ap)
dd = dvp->v_data;
error = ENOENT;
sx_xlock(&dmp->dm_lock);
TAILQ_FOREACH(de, &dd->de_dlist, de_list) {
if (cnp->cn_namelen != de->de_dirent->d_namlen)
continue;
@ -621,6 +681,7 @@ devfs_mknod(struct vop_mknod_args *ap)
goto notfound;
de->de_flags &= ~DE_WHITEOUT;
error = devfs_allocv(de, dvp->v_mount, vpp, td);
return (error);
notfound:
sx_xunlock(&dmp->dm_lock);
return (error);
@ -1124,9 +1185,7 @@ devfs_symlink(struct vop_symlink_args *ap)
mac_create_devfs_symlink(ap->a_cnp->cn_cred, dmp->dm_mount, dd, de);
#endif
TAILQ_INSERT_TAIL(&dd->de_dlist, de, de_list);
devfs_allocv(de, ap->a_dvp->v_mount, ap->a_vpp, td);
sx_xunlock(&dmp->dm_lock);
return (0);
return (devfs_allocv(de, ap->a_dvp->v_mount, ap->a_vpp, td));
}
/* ARGSUSED */