Mark Fasheh
2014-Dec-19 20:25 UTC
[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages
On Fri, Dec 19, 2014 at 04:34:39PM +0800, jiangyiwen wrote:> ? 2014/12/17 6:26, Mark Fasheh ??: > > 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
jiangyiwen
2014-Dec-20 09:39 UTC
[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages
? 2014/12/20 4:25, Mark Fasheh ??:> On Fri, Dec 19, 2014 at 04:34:39PM +0800, jiangyiwen wrote: >> ? 2014/12/17 6:26, Mark Fasheh ??: >>> 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() >But at this time, it has already called dlm_purge_lockres(). The reasons are as follows: 1) lockres is created in dlm_init_lockres(), it call kref_init(), count is 1; 2) Only when lockres is unused, it will call dlm_lockres_put() twice by dlm_run_purge_list(). So dlm_purge_lockres() has been called if the count goes to zero.> 3) dlm_lockres_release() will free the lockres without removing it from the > tracking list. Thus we will have a corrupted list. >Without this scene. dlm_purge_lockres() is called before dlm_lockres_release().> Does that make sense? Am I wrong here? > --Mark > > -- > Mark Fasheh > > . >