From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xue jiufei Date: Tue, 23 Dec 2014 14:06:25 +0800 Subject: [Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages In-Reply-To: <549543BB.2060707@huawei.com> References: <548f65d4.jhly8vWOTpWuHPjg%akpm@linux-foundation.org> <20141216222629.GO7238@wotan.suse.de> <5493E31F.2000509@huawei.com> <20141219202503.GX7238@wotan.suse.de> <549543BB.2060707@huawei.com> Message-ID: <54990661.4090303@huawei.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ocfs2-devel@oss.oracle.com Hi jiangyiwen, On 2014/12/20 17:39, jiangyiwen wrote: > ? 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(). Once lock resource is inserted into hash list, it should call dlm_purge_lockres()->__dlm_unhash_lockres() to put the last ref. However, if lock resource is initialized and inserted into tracking list but not inserted into hash list, it can happen that dlm_lockres_release() will free the lockres without removing it from the tracking list. So we should remove lockres from tracking list if we call dlm_lockres_put() after lockres is created but not inserted into hash list yet. Thanks, Xuejiufei >> Does that make sense? Am I wrong here? >> --Mark >> >> -- >> Mark Fasheh >> >> . >> > > > > _______________________________________________ > Ocfs2-devel mailing list > Ocfs2-devel at oss.oracle.com > https://oss.oracle.com/mailman/listinfo/ocfs2-devel >