Date: Fri, 28 Apr 2006 18:57:49 -0400 From: Alexander Kabaev <kabaev@gmail.com> To: Kostik Belousov <kostikbel@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: vn_lock & ffs_snapremove Message-ID: <20060428185749.171da2bc@kan.dnsalias.net> In-Reply-To: <20060428130030.GC1270@deviant.kiev.zoral.com.ua> References: <20060428130030.GC1270@deviant.kiev.zoral.com.ua>
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On Fri, 28 Apr 2006 16:00:30 +0300
Kostik Belousov <kostikbel@gmail.com> wrote:
> Look at the two code fragments
>=20
> 1. from vn_lock(9):
>=20
> error =3D VOP_LOCK(vp, flags | LK_INTERLOCK, td);
> flags &=3D ~LK_INTERLOCK;
> KASSERT((flags & LK_RETRY) =3D=3D 0 || error =3D=3D 0,
> ("LK_RETRY set with incompatible flags %d\n",
> flags)); /*
> * Callers specify LK_RETRY if they wish to get dead
> vnodes.
> * If RETRY is not set, we return ENOENT instead.
> */
> if (error =3D=3D 0 && vp->v_iflag & VI_DOOMED &&
> (flags & LK_RETRY) =3D=3D 0) {
> VOP_UNLOCK(vp, 0, td);
> error =3D ENOENT;
> break;
> }
>=20
> 2. ffs_snapremove(9):
>=20
> (vp->v_vnlock for snapshot vnode vp points to sn_snlock)
> lkp =3D vp->v_vnlock;
> vp->v_vnlock =3D &vp->v_lock;
>=20
> Is there anything that would prevent these two fragments to
> intervene ? Esp. bad looks the situation where VOP_LOCK() from
> vn_lock executed and locked doomed snapshot vnode, after that
> ffs_snapremove replaces vnode lock and VOP_UNLOCK attempted on
> _another_ lock.
>=20
> If this scenario can happen (as it seems), then, probably,
> some measures like transferlockers(9) are needed ?
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Alexander Kabaev
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