From mboxrd@z Thu Jan 1 00:00:00 1970 From: piaojun Date: Fri, 15 Feb 2019 15:35:04 +0800 Subject: [Ocfs2-devel] [PATCH] ocfs2/dlm: return DLM_CANCELGRANT if the lock is on granted list and the operation is canceled In-Reply-To: <63ADC13FD55D6546B7DECE290D39E37301278541E8@H3CMLB14-EX.srv.huawei-3com.com> References: <98f0e80c-9c13-dbb6-047c-b40e100082b1@huawei.com> <63ADC13FD55D6546B7DECE290D39E37301277EFAA1@H3CMLB12-EX.srv.huawei-3com.com> <00607177-cb1b-d380-e6d3-3d5cb9b3c991@huawei.com> <63ADC13FD55D6546B7DECE290D39E37301277F1589@H3CMLB12-EX.srv.huawei-3com.com> <7420155e-f7d6-520c-5134-4a681399a68a@huawei.com> <5C652F12.9010408@huawei.com> <63ADC13FD55D6546B7DECE290D39E37301278538DD@H3CMLB14-EX.srv.huawei-3com.com> <5C666142.7000100@huawei.com> <63ADC13FD55D6546B7DECE290D39E37301278541E8@H3CMLB14-EX.srv.huawei-3com.com> Message-ID: <5C666BA8.4030403@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 Changwei, On 2019/2/15 15:06, Changwei Ge wrote: > Hi Jun, > > On 2019/2/15 14:51, piaojun wrote: >> Hi Changwei, >> >> On 2019/2/14 18:13, Changwei Ge wrote: >>> On 2019/2/14 17:09, piaojun wrote: >>>> Hi Changwei, >>>> >>>> The problem can't be solved completely if clear ::cancel_pending in >>>> dlm_proxy_ast_handler, as AST will come at anytime just before >>> >>> So how about also add check here bere setting ::cancel_pending in dlmunlock_common() before invoking dlm_send_remote_unlock_request(). >>> If already on grant list just return DLM_CANCELGRANT >>> >>> Then a further reference code might look like: >>> >>> root at ubuntu16:/home/chge/linux[master]# git diff >>> diff --git a/fs/ocfs2/dlm/dlmast.c b/fs/ocfs2/dlm/dlmast.c >>> index 39831fc..812843b 100644 >>> --- a/fs/ocfs2/dlm/dlmast.c >>> +++ b/fs/ocfs2/dlm/dlmast.c >>> @@ -372,8 +372,11 @@ int dlm_proxy_ast_handler(struct o2net_msg *msg, u32 len, void *data, >>> head = &res->converting; >>> lock = NULL; >>> list_for_each_entry(lock, head, list) { >>> - if (lock->ml.cookie == cookie) >>> + if (lock->ml.cookie == cookie) { >>> + if (lock->cancel_pending) >>> + lock->cancel_pending = 0; >>> goto do_ast; >>> + } >>> } >>> >>> /* if not on convert, try blocked for ast, granted for bast */ >>> diff --git a/fs/ocfs2/dlm/dlmunlock.c b/fs/ocfs2/dlm/dlmunlock.c >>> index c8e9b70..b4728b5 100644 >>> --- a/fs/ocfs2/dlm/dlmunlock.c >>> +++ b/fs/ocfs2/dlm/dlmunlock.c >>> @@ -174,9 +174,14 @@ static enum dlm_status dlmunlock_common(struct dlm_ctxt *dlm, >>> if (!master_node) { >>> owner = res->owner; >>> /* drop locks and send message */ >>> - if (flags & LKM_CANCEL) >>> + if (flags & LKM_CANCEL) { >>> + if (dlm_lock_on_list(&res->granted, lock)) { >>> + status = DLM_CANCELGRANT; >>> + goto leave; >> >> If master dead and then lockres is moved to granted list in >> dlm_move_lockres_to_recovery_list, the OCFS2_LOCK_BUSY is not cleared. > > OCFS2_LOCK_BUSY should be cleared in ocfs2_locking_ast() since previous locking AST has come back(moving lock to grant list). > That's why we return DLM_CANCELGRANT to caller to avoid calling AST. Otherwise ast() will be called twice, which is obviously a BUG. I mean master is already dead and ast won't come. So the OCFS2_LOCK_BUSY is not cleared. And there are two cases that lockres is moved to grant list: 1. AST comes back and OCFS2_LOCK_BUSY is cleared. 2. AST does not come back and OCFS2_LOCK_BUSY remains, recovery process move it to grant list. In this case, we need do AST for it. Perhaps we need do AST again for it. > >> And this will cause stuck problem when ocfs2_drop_lock. The reason is >> that unlock ast won't be done when DLM_CANCELGRANT is set. So I think > > With above elaboration, you don't have to worry the hang issue anymore. > > Thanks, > Changwei > >> we need distinguish all the cases of moving lockres to grant list. >> >>> + } >>> + >>> lock->cancel_pending = 1; >>> - else >>> + } else >>> lock->unlock_pending = 1; >>> spin_unlock(&lock->spinlock); >>> spin_unlock(&res->spinlock); >>> >>> >>> >>> Thanks, >>> Changwei >>> >>>> ::cancel_pendig is set. If there is not any other better solutions, >>>> could we accept this patch? This bug is very harmful. >>>> >>>> Thanks, >>>> Jun >>>> >>>> On 2018/12/8 18:05, wangjian wrote: >>>>> Hi Changwei, >>>>> >>>>> I understand your idea. But we should be aware that the cancel_convert process and >>>>> other processes (accepting the AST process, the recovery process) are asynchronous. >>>>> For example, according to your idea, check if the lock is in the grant queue before >>>>> calling the dlm_send_remote_unlock_request function in the dlm_proxy_ast_handler function. >>>>> Then decide whether to clear cancel_pending. But if the AST does not come at this time, >>>>> the check passes and cancel_pendig will not be cleared. Then AST immediately came over again, >>>>> which also led to a bug. I personally think that for asynchronous processes we can't guarantee >>>>> the speed of execution of each process. All we can do is to avoid the BUG scene. >>>>> >>>>> As for the question you said ("If you remove the BUG check why you still call dlm_commit_pending_cancel() >>>>> to move the lock back to grant on matter it's on converting list or not?"). >>>>> I think we should first check if the lock is in the grant queue >>>>> (at this time, dlm->spinlock and res->spinlock have been added), then decide whether to call >>>>> dlm_commit_pending_cancel function. >>>>> >>>>> Thanks, >>>>> Jian >>>>> >>>>> On 12/7/2018 11:12 AM, Changwei Ge wrote: >>>>>> Hi Jian, >>>>>> >>>>>> I suppose that the situation you described truly exists. >>>>>> But the way you fix the issue is not in my favor. >>>>>> >>>>>> If you remove the BUG check why you still call dlm_commit_pending_cancel() to >>>>>> move the lock back to grant on matter it's on converting list or not? >>>>>> >>>>>> So how about keeping the BUG check in dlm_move_lockres_to_recovery_list(). >>>>>> If the locking _ast_ comes back very fast just check ::cancel_pending in dlm_proxy_ast_handler() and clear it. >>>>>> Then with the logic checking if the lock is on grant list (in dlmunlock_common() more less like your current method) >>>>>> or not we can easily tell if the cancellation succeeds or not. >>>>>> >>>>>> That complies the original dlm design, which I think is better and easier for maintainers to understand. >>>>>> >>>>>> Thanks, >>>>>> Changwei >>>>>> >>>>>> On 2018/12/6 20:06, wangjian wrote: >>>>>>> Hi Changwei, >>>>>>> >>>>>>> I don't fully agree with your point of view. In my opinion, the lock cancellation process and the lock >>>>>>> conversion process are asynchronous. We can't guarantee that the lock must be in the convert list >>>>>>> during the lock conversion process, otherwise this BUG will not happen. >>>>>>> So, I think this is a meaningless BUG. >>>>>>> >>>>>>> Thanks, >>>>>>> Jian >>>>>>> >>>>>>> On 12/5/2018 9:49 AM, Changwei Ge wrote: >>>>>>>> Hi Jian, >>>>>>>> >>>>>>>> I suppose you can't just remove the BUG_ON() check. >>>>>>>> If you remove it, below code violates the original logic. >>>>>>>> >>>>>>>> ''' >>>>>>>> 2141 dlm_commit_pending_cancel(res, lock); >>>>>>>> ''' >>>>>>>> >>>>>>>> What's more important is *locking cancel* must be against a *locking conversion* progress. >>>>>>>> So it makes sense to check if this lock is on converting list. >>>>>>>> >>>>>>>> So I have to NACK to this patch. >>>>>>>> >>>>>>>> Thanks, >>>>>>>> Changwei >>>>>>>> >>>>>>>> >>>>>>>> On 2018/12/3 20:23, wangjian wrote: >>>>>>>>> In the dlm_move_lockres_to_recovery_list function, if the lock >>>>>>>>> is in the granted queue and cancel_pending is set, it will >>>>>>>>> encounter a BUG. I think this is a meaningless BUG, >>>>>>>>> so be prepared to remove it. A scenario that causes >>>>>>>>> this BUG will be given below. >>>>>>>>> >>>>>>>>> At the beginning, Node 1 is the master and has NL lock, >>>>>>>>> Node 2 has PR lock, Node 3 has PR lock too. >>>>>>>>> >>>>>>>>> Node 1 Node 2 Node 3 >>>>>>>>> want to get EX lock. >>>>>>>>> >>>>>>>>> want to get EX lock. >>>>>>>>> >>>>>>>>> Node 3 hinder >>>>>>>>> Node 2 to get >>>>>>>>> EX lock, send >>>>>>>>> Node 3 a BAST. >>>>>>>>> >>>>>>>>> receive BAST from >>>>>>>>> Node 1. downconvert >>>>>>>>> thread begin to >>>>>>>>> cancel PR to EX conversion. >>>>>>>>> In dlmunlock_common function, >>>>>>>>> downconvert thread has set >>>>>>>>> lock->cancel_pending, >>>>>>>>> but did not enter >>>>>>>>> dlm_send_remote_unlock_request >>>>>>>>> function. >>>>>>>>> >>>>>>>>> Node2 dies because >>>>>>>>> the host is powered down. >>>>>>>>> >>>>>>>>> In recovery process, >>>>>>>>> clean the lock that >>>>>>>>> related to Node2. >>>>>>>>> then finish Node 3 >>>>>>>>> PR to EX request. >>>>>>>>> give Node 3 a AST. >>>>>>>>> >>>>>>>>> receive AST from Node 1. >>>>>>>>> change lock level to EX, >>>>>>>>> move lock to granted list. >>>>>>>>> >>>>>>>>> Node1 dies because >>>>>>>>> the host is powered down. >>>>>>>>> >>>>>>>>> In dlm_move_lockres_to_recovery_list >>>>>>>>> function. the lock is in the >>>>>>>>> granted queue and cancel_pending >>>>>>>>> is set. BUG_ON. >>>>>>>>> >>>>>>>>> But after clearing this BUG, process will encounter >>>>>>>>> the second BUG in the ocfs2_unlock_ast function. >>>>>>>>> Here is a scenario that will cause the second BUG >>>>>>>>> in ocfs2_unlock_ast as follows: >>>>>>>>> >>>>>>>>> At the beginning, Node 1 is the master and has NL lock, >>>>>>>>> Node 2 has PR lock, Node 3 has PR lock too. >>>>>>>>> >>>>>>>>> Node 1 Node 2 Node 3 >>>>>>>>> want to get EX lock. >>>>>>>>> >>>>>>>>> want to get EX lock. >>>>>>>>> >>>>>>>>> Node 3 hinder >>>>>>>>> Node 2 to get >>>>>>>>> EX lock, send >>>>>>>>> Node 3 a BAST. >>>>>>>>> >>>>>>>>> receive BAST from >>>>>>>>> Node 1. downconvert >>>>>>>>> thread begin to >>>>>>>>> cancel PR to EX conversion. >>>>>>>>> In dlmunlock_common function, >>>>>>>>> downconvert thread has released >>>>>>>>> lock->spinlock and res->spinlock, >>>>>>>>> but did not enter >>>>>>>>> dlm_send_remote_unlock_request >>>>>>>>> function. >>>>>>>>> >>>>>>>>> Node2 dies because >>>>>>>>> the host is powered down. >>>>>>>>> >>>>>>>>> In recovery process, >>>>>>>>> clean the lock that >>>>>>>>> related to Node2. >>>>>>>>> then finish Node 3 >>>>>>>>> PR to EX request. >>>>>>>>> give Node 3 a AST. >>>>>>>>> >>>>>>>>> receive AST from Node 1. >>>>>>>>> change lock level to EX, >>>>>>>>> move lock to granted list, >>>>>>>>> set lockres->l_unlock_action >>>>>>>>> as OCFS2_UNLOCK_INVALID >>>>>>>>> in ocfs2_locking_ast function. >>>>>>>>> >>>>>>>>> Node2 dies because >>>>>>>>> the host is powered down. >>>>>>>>> >>>>>>>>> Node 3 realize that Node 1 >>>>>>>>> is dead, remove Node 1 from >>>>>>>>> domain_map. downconvert thread >>>>>>>>> get DLM_NORMAL from >>>>>>>>> dlm_send_remote_unlock_request >>>>>>>>> function and set *call_ast as 1. >>>>>>>>> Then downconvert thread meet >>>>>>>>> BUG in ocfs2_unlock_ast function. >>>>>>>>> >>>>>>>>> To avoid meet the second BUG, function dlmunlock_common shuold >>>>>>>>> return DLM_CANCELGRANT if the lock is on granted list and >>>>>>>>> the operation is canceled. >>>>>>>>> >>>>>>>>> Signed-off-by: Jian Wang >>>>>>>>> Reviewed-by: Yiwen Jiang >>>>>>>>> --- >>>>>>>>> fs/ocfs2/dlm/dlmrecovery.c | 1 - >>>>>>>>> fs/ocfs2/dlm/dlmunlock.c | 5 +++++ >>>>>>>>> 2 files changed, 5 insertions(+), 1 deletion(-) >>>>>>>>> >>>>>>>>> diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c >>>>>>>>> index 802636d..7489652 100644 >>>>>>>>> --- a/fs/ocfs2/dlm/dlmrecovery.c >>>>>>>>> +++ b/fs/ocfs2/dlm/dlmrecovery.c >>>>>>>>> @@ -2134,7 +2134,6 @@ void dlm_move_lockres_to_recovery_list(struct dlm_ctxt *dlm, >>>>>>>>> * if this had completed successfully >>>>>>>>> * before sending this lock state to the >>>>>>>>> * new master */ >>>>>>>>> - BUG_ON(i != DLM_CONVERTING_LIST); >>>>>>>>> mlog(0, "node died with cancel pending " >>>>>>>>> "on %.*s. move back to granted list.\n", >>>>>>>>> res->lockname.len, res->lockname.name); >>>>>>>>> diff --git a/fs/ocfs2/dlm/dlmunlock.c b/fs/ocfs2/dlm/dlmunlock.c >>>>>>>>> index 63d701c..505bb6c 100644 >>>>>>>>> --- a/fs/ocfs2/dlm/dlmunlock.c >>>>>>>>> +++ b/fs/ocfs2/dlm/dlmunlock.c >>>>>>>>> @@ -183,6 +183,11 @@ static enum dlm_status dlmunlock_common(struct dlm_ctxt *dlm, >>>>>>>>> flags, owner); >>>>>>>>> spin_lock(&res->spinlock); >>>>>>>>> spin_lock(&lock->spinlock); >>>>>>>>> + >>>>>>>>> + if ((flags & LKM_CANCEL) && >>>>>>>>> + dlm_lock_on_list(&res->granted, lock)) >>>>>>>>> + status = DLM_CANCELGRANT; >>>>>>>>> + >>>>>>>>> /* if the master told us the lock was already granted, >>>>>>>>> * let the ast handle all of these actions */ >>>>>>>>> if (status == DLM_CANCELGRANT) { >>>>>>>>> -- >>>>>>>>> 1.8.3.1 >>>>>>>>> >>>>>>>> . >>>>>>>> >>>>>> . >>>>>> >>>>> >>>>> >>>>> _______________________________________________ >>>>> Ocfs2-devel mailing list >>>>> Ocfs2-devel at oss.oracle.com >>>>> https://oss.oracle.com/mailman/listinfo/ocfs2-devel >>>>> >>>> >>> . >>> >> > . >