On 13 Oct, Don Lewis wrote: > The bug is that once we have unlocked pdp, another thread can do a > lookup and overwrite dp->i_ino, so instead of getting the vnode for the > ".." directory entry, VFS_VGET() will return the vnode for a > subdirectory of the current directory, and when we relock the current > directory we'll have a lock order reversal. > > Even if this doesn't result in a deadlock, it looks like it has the > potential for mucking up lookups that involve "..". I also don't > currently see a way for this to become a vnode lock leak. I think the leak happens when dp->i_ino gets overwritten by the inode number for ".". This causes ufs_lookup() to recurse on the lock for the current directory vnode (the lock is first acquired by VFS_VGET() and then recursed by vn_lock()). This isn't expected by lookup(), which compares whether the vnode returned by VOP_LOOKUP() is the same as the directory vnode and uses this information to decide whether to call vput() or vrele(). > The fix is to preserve a copy of dp->d_ino before unlocking pdp, > and pass the saved value to VFS_VGET(). > > Index: sys/ufs/ufs/ufs_lookup.c > =================================================================== > RCS file: /home/ncvs/src/sys/ufs/ufs/ufs_lookup.c,v > retrieving revision 1.77 > diff -u -r1.77 ufs_lookup.c > --- sys/ufs/ufs/ufs_lookup.c 13 Apr 2005 10:59:09 -0000 1.77 > +++ sys/ufs/ufs/ufs_lookup.c 13 Oct 2005 23:20:59 -0000 > _at__at_ -153,6 +153,7 _at__at_ > int flags = cnp->cn_flags; > int nameiop = cnp->cn_nameiop; > struct thread *td = cnp->cn_thread; > + u_int32_t saved_ino; > > bp = NULL; > slotoffset = -1; > _at__at_ -557,8 +558,9 _at__at_ > */ > pdp = vdp; > if (flags & ISDOTDOT) { > + saved_ino = dp->i_ino; > VOP_UNLOCK(pdp, 0, td); /* race to get the inode */ > - error = VFS_VGET(pdp->v_mount, dp->i_ino, > + error = VFS_VGET(pdp->v_mount, saved_ino, > cnp->cn_lkflags, &tdp); > vn_lock(pdp, LK_EXCLUSIVE | LK_RETRY, td); > if (error)Received on Fri Oct 14 2005 - 15:56:59 UTC
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