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Fix the remaining race in the revs. 1.232, 1,233 that could occur during

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unmount when mp structure is reused while waiting for coveredvp lock.
Introduce struct mount generation count, increment it on each reuse and
compare the generations before and after obtaining the coveredvp lock.

Reviewed by:	tegge, pjd
Approved by:	pjd (mentor)
MFC after:	2 weeks
This commit is contained in:
Konstantin Belousov 2006-10-03 10:47:04 +00:00
parent 9a3fc40a26
commit 30af71199e
2 changed files with 6 additions and 1 deletions
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6
sys/kern/vfs_mount.c
View File

@ -475,6 +475,7 @@ vfs_mount_alloc(struct vnode *vp, struct vfsconf *vfsp,
MNT_ILOCK(mp);
mp->mnt_flag |= vfsp->vfc_flags & MNT_VISFLAGMASK;
MNT_IUNLOCK(mp);
mp->mnt_gen++;
strlcpy(mp->mnt_stat.f_fstypename, vfsp->vfc_name, MFSNAMELEN);
mp->mnt_vnodecovered = vp;
mp->mnt_cred = crdup(td->td_ucred);
@ -1148,10 +1149,12 @@ dounmount(mp, flags, td)
struct vnode *coveredvp, *fsrootvp;
int error;
int async_flag;
int mnt_gen_r;
mtx_assert(&Giant, MA_OWNED);
if ((coveredvp = mp->mnt_vnodecovered) != NULL) {
mnt_gen_r = mp->mnt_gen;
VI_LOCK(coveredvp);
vholdl(coveredvp);
error = vn_lock(coveredvp, LK_EXCLUSIVE | LK_INTERLOCK, td);
@ -1162,7 +1165,8 @@ dounmount(mp, flags, td)
*/
if (error)
return (error);
if (coveredvp->v_mountedhere != mp) {
if (coveredvp->v_mountedhere != mp ||
coveredvp->v_mountedhere->mnt_gen != mnt_gen_r) {
VOP_UNLOCK(coveredvp, 0, td);
return (EBUSY);
}

1
sys/sys/mount.h
View File

@ -145,6 +145,7 @@ struct vfsopt;
struct mount {
struct lock mnt_lock; /* mount structure lock */
struct mtx mnt_mtx; /* mount structure interlock */
int mnt_gen; /* struct mount generation */
#define mnt_startzero mnt_list
TAILQ_ENTRY(mount) mnt_list; /* (m) mount list */
struct vfsops *mnt_op; /* operations on fs */