[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages
Mark Fasheh
mfasheh at suse.de
Fri Dec 19 12:25:03 PST 2014
On Fri, Dec 19, 2014 at 04:34:39PM +0800, jiangyiwen wrote:
> 在 2014/12/17 6:26, Mark Fasheh 写道:
> > On Mon, Dec 15, 2014 at 02:51:00PM -0800, Andrew Morton wrote:
> >> In such a race case, invalid address access may occurs. So we should
> >> delete list res->tracking before resA->refs decrease to 0.
> >>
> >
> >
> >> diff -puN fs/ocfs2/dlm/dlmmaster.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages fs/ocfs2/dlm/dlmmaster.c
> >> --- a/fs/ocfs2/dlm/dlmmaster.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages
> >> +++ a/fs/ocfs2/dlm/dlmmaster.c
> >> @@ -498,16 +498,6 @@ static void dlm_lockres_release(struct k
> >> mlog(0, "destroying lockres %.*s\n", res->lockname.len,
> >> res->lockname.name);
> >>
> >> - spin_lock(&dlm->track_lock);
> >> - if (!list_empty(&res->tracking))
> >> - list_del_init(&res->tracking);
> >> - else {
> >> - mlog(ML_ERROR, "Resource %.*s not on the Tracking list\n",
> >> - res->lockname.len, res->lockname.name);
> >> - dlm_print_one_lock_resource(res);
> >> - }
> >> - spin_unlock(&dlm->track_lock);
> >> -
> >> atomic_dec(&dlm->res_cur_count);
> >>
> >> if (!hlist_unhashed(&res->hash_node) ||
> >> diff -puN fs/ocfs2/dlm/dlmthread.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages fs/ocfs2/dlm/dlmthread.c
> >> --- a/fs/ocfs2/dlm/dlmthread.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages
> >> +++ a/fs/ocfs2/dlm/dlmthread.c
> >> @@ -211,6 +211,16 @@ static void dlm_purge_lockres(struct dlm
> >>
> >> __dlm_unhash_lockres(dlm, res);
> >>
> >> + spin_lock(&dlm->track_lock);
> >> + if (!list_empty(&res->tracking))
> >> + list_del_init(&res->tracking);
> >> + else {
> >> + mlog(ML_ERROR, "Resource %.*s not on the Tracking list\n",
> >> + res->lockname.len, res->lockname.name);
> >> + __dlm_print_one_lock_resource(res);
> >> + }
> >> + spin_unlock(&dlm->track_lock);
> >> +
> >> /* lockres is not in the hash now. drop the flag and wake up
> >> * any processes waiting in dlm_get_lock_resource. */
> >> if (!master) {
> >> _
> >
> > How do we know that dlm_purge_lockres() is the last caller of
> > dlm_lockres_put()? Don't we now have a problem where if the last ref is
> > dropped by any other function than dlm_purge_lockres() the lockres is freed
> > while on the tracking list?
> > --Mark
> >
> > --
> > Mark Fasheh
> >
> > .
> >
> dlm_purge_lockres is not necessarily the last caller of
> dlm_lockres_put(), but it means lockres will be purged if
> dlm_purge_lockres is called. Besides, lockres is also unhashed in
> dlm_purge_lockres, so lockres can be removed from tracking list.
> contents of dlm->tracking_list will be consistent with
> dlm->lockres_hash.
I'm still confused. This is what I'm worried about:
1) a procss calls dlm_lockres_put(), NOT from dlm_purge_lockres().
2) if the count goes to zero, then that process will call dlm_lockres_release()
3) dlm_lockres_release() will free the lockres without removing it from the
tracking list. Thus we will have a corrupted list.
Does that make sense? Am I wrong here?
--Mark
--
Mark Fasheh
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