From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tao Ma Date: Mon, 21 Jun 2010 15:33:10 +0800 Subject: [Ocfs2-devel] [PATCH] ocfs2/dlm: remove potential deadlock In-Reply-To: <20100621053139.GA2809@laptop.us.oracle.com> References: <201006160654.o5G1s1E0006164@acsinet15.oracle.com> <20100621053139.GA2809@laptop.us.oracle.com> Message-ID: <4C1F15B6.9030007@oracle.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 wengang, On 06/21/2010 01:31 PM, Wengang Wang wrote: > Why atomic operations on dlm_refs need spinlock's protect? > > /* NOTE: Next three are protected by dlm_domain_lock */ > struct kref dlm_refs; > enum dlm_ctxt_state dlm_state; > unsigned int num_joins; I don't dive into the code, so if there is something wrong, please correct me. AFAICS, kref_put isn't an atomic operation, it need to call release to free the container of kref. Regards, Tao > > regards, > wengang. > > On 10-06-16 14:52, Wengang Wang wrote: >> When we need to take both dlm_domain_lock and dlm->spinlock, we should take >> them in order of: >> dlm_domain_lock then dlm->spinlock. >> >> There is pathes disobey this order. That is calling dlm_lockres_put with dlm-> >> spinlock held. dlm_lockres_put() finally calls dlm_put() which take >> dlm_domain_lock. >> >> The fix is moving the locking on dlm_domain_lock to dlm_ctxt_release() from >> dlm_put(). dlm_ctxt_release() is only called on the release of the last >> reference. Any path should not be holding dlm->spinlock when dropping the "last" >> reference. >> >> Signed-off-by: Wengang Wang >> --- >> fs/ocfs2/dlm/dlmdomain.c | 12 ++++-------- >> 1 files changed, 4 insertions(+), 8 deletions(-) >> >> diff --git a/fs/ocfs2/dlm/dlmdomain.c b/fs/ocfs2/dlm/dlmdomain.c >> index ab82add..754baf2 100644 >> --- a/fs/ocfs2/dlm/dlmdomain.c >> +++ b/fs/ocfs2/dlm/dlmdomain.c >> @@ -321,28 +321,24 @@ static void dlm_ctxt_release(struct kref *kref) >> >> dlm = container_of(kref, struct dlm_ctxt, dlm_refs); >> >> + if (spin_is_locked(&dlm->spinlock)) >> + BUG(); >> BUG_ON(dlm->num_joins); >> BUG_ON(dlm->dlm_state == DLM_CTXT_JOINED); >> >> + spin_lock(&dlm_domain_lock); >> /* we may still be in the list if we hit an error during join. */ >> list_del_init(&dlm->list); >> - >> spin_unlock(&dlm_domain_lock); >> >> - mlog(0, "freeing memory from domain %s\n", dlm->name); >> - >> wake_up(&dlm_domain_events); >> - >> + mlog(0, "freeing memory from domain %s\n", dlm->name); >> dlm_free_ctxt_mem(dlm); >> - >> - spin_lock(&dlm_domain_lock); >> } >> >> void dlm_put(struct dlm_ctxt *dlm) >> { >> - spin_lock(&dlm_domain_lock); >> kref_put(&dlm->dlm_refs, dlm_ctxt_release); >> - spin_unlock(&dlm_domain_lock); >> } >> >> static void __dlm_get(struct dlm_ctxt *dlm) >> -- >> 1.6.6.1 >> >> >> _______________________________________________ >> Ocfs2-devel mailing list >> Ocfs2-devel at oss.oracle.com >> http://oss.oracle.com/mailman/listinfo/ocfs2-devel > > _______________________________________________ > Ocfs2-devel mailing list > Ocfs2-devel at oss.oracle.com > http://oss.oracle.com/mailman/listinfo/ocfs2-devel