From: Chao Leng <lengchao@huawei.com> To: Hannes Reinecke <hare@suse.de>, Sagi Grimberg <sagi@grimberg.me>, "Daniel Wagner" <dwagner@suse.de> Cc: <linux-nvme@lists.infradead.org>, <linux-kernel@vger.kernel.org>, "Jens Axboe" <axboe@fb.com>, Keith Busch <kbusch@kernel.org>, Christoph Hellwig <hch@lst.de> Subject: Re: [PATCH v2] nvme-multipath: Early exit if no path is available Date: Tue, 2 Feb 2021 09:12:30 +0800 [thread overview] Message-ID: <6ef6df55-318b-887d-b14f-62cae6419b4a@huawei.com> (raw) In-Reply-To: <2752ed93-6bd5-1a13-0e05-b91e2dcc24e1@suse.de> On 2021/2/1 18:45, Hannes Reinecke wrote: > On 2/1/21 10:40 AM, Chao Leng wrote: >> >> >> On 2021/2/1 16:57, Hannes Reinecke wrote: >>> On 2/1/21 9:47 AM, Chao Leng wrote: >>>> >>>> >>>> On 2021/2/1 15:29, Hannes Reinecke wrote:[ .. ] >>>>> Urgh. Please, no. That is well impossible to debug. >>>>> Can you please open-code it to demonstrate where the difference to the current (and my fixed) versions is? >>>>> I'm still not clear where the problem is once we applied both patches. >>>> For example assume the list has three path, and all path is not NVME_ANA_OPTIMIZED: >>>> head->next = ns1; >>>> ns1->next = ns2; >>>> ns2->next = head; >>>> old->next = ns2; >>>> >>> And this is where I have issues with. >>> Where does 'old' come from? >>> Clearly it was part of the list at one point; so what happened to it? >> I explained this earlier. >> In nvme_ns_remove, there is a hole between list_del_rcu and >> nvme_mpath_clear_current_path. If head->current_path is the "old", and >> the "old" is removing. The "old" is already removed from the list by >> list_del_rcu, but head->current_path is not clear to NULL by >> nvme_mpath_clear_current_path. >> Find path is race with nvme_ns_remove, use the "old" pass to >> nvme_round_robin_path to find path. > > Ah. So this should be better: > > @@ -202,10 +202,12 @@ static struct nvme_ns *__nvme_find_path(struct nvme_ns_head *head, int node) > static struct nvme_ns *nvme_next_ns(struct nvme_ns_head *head, > struct nvme_ns *ns) > { > - ns = list_next_or_null_rcu(&head->list, &ns->siblings, struct nvme_ns, > - siblings); > - if (ns) > - return ns; > + if (ns && !test_bit(NVME_NS_REMOVING, &ns->flags)) { > + ns = list_next_or_null_rcu(&head->list, &ns->siblings, > + struct nvme_ns, siblings); > + if (ns) > + return ns; > + } > return list_first_or_null_rcu(&head->list, struct nvme_ns, siblings); > } > > The 'NVME_NS_REMOVING' bit is set before list_del_rcu() is called, so it should guard against the issue you mentioned. Looks useless, it is still infinite loop. You can check the workflow for the scenario I mentioned. > > Cheers, > > Hannes
WARNING: multiple messages have this Message-ID (diff)
From: Chao Leng <lengchao@huawei.com> To: Hannes Reinecke <hare@suse.de>, Sagi Grimberg <sagi@grimberg.me>, "Daniel Wagner" <dwagner@suse.de> Cc: Jens Axboe <axboe@fb.com>, Keith Busch <kbusch@kernel.org>, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, Christoph Hellwig <hch@lst.de> Subject: Re: [PATCH v2] nvme-multipath: Early exit if no path is available Date: Tue, 2 Feb 2021 09:12:30 +0800 [thread overview] Message-ID: <6ef6df55-318b-887d-b14f-62cae6419b4a@huawei.com> (raw) In-Reply-To: <2752ed93-6bd5-1a13-0e05-b91e2dcc24e1@suse.de> On 2021/2/1 18:45, Hannes Reinecke wrote: > On 2/1/21 10:40 AM, Chao Leng wrote: >> >> >> On 2021/2/1 16:57, Hannes Reinecke wrote: >>> On 2/1/21 9:47 AM, Chao Leng wrote: >>>> >>>> >>>> On 2021/2/1 15:29, Hannes Reinecke wrote:[ .. ] >>>>> Urgh. Please, no. That is well impossible to debug. >>>>> Can you please open-code it to demonstrate where the difference to the current (and my fixed) versions is? >>>>> I'm still not clear where the problem is once we applied both patches. >>>> For example assume the list has three path, and all path is not NVME_ANA_OPTIMIZED: >>>> head->next = ns1; >>>> ns1->next = ns2; >>>> ns2->next = head; >>>> old->next = ns2; >>>> >>> And this is where I have issues with. >>> Where does 'old' come from? >>> Clearly it was part of the list at one point; so what happened to it? >> I explained this earlier. >> In nvme_ns_remove, there is a hole between list_del_rcu and >> nvme_mpath_clear_current_path. If head->current_path is the "old", and >> the "old" is removing. The "old" is already removed from the list by >> list_del_rcu, but head->current_path is not clear to NULL by >> nvme_mpath_clear_current_path. >> Find path is race with nvme_ns_remove, use the "old" pass to >> nvme_round_robin_path to find path. > > Ah. So this should be better: > > @@ -202,10 +202,12 @@ static struct nvme_ns *__nvme_find_path(struct nvme_ns_head *head, int node) > static struct nvme_ns *nvme_next_ns(struct nvme_ns_head *head, > struct nvme_ns *ns) > { > - ns = list_next_or_null_rcu(&head->list, &ns->siblings, struct nvme_ns, > - siblings); > - if (ns) > - return ns; > + if (ns && !test_bit(NVME_NS_REMOVING, &ns->flags)) { > + ns = list_next_or_null_rcu(&head->list, &ns->siblings, > + struct nvme_ns, siblings); > + if (ns) > + return ns; > + } > return list_first_or_null_rcu(&head->list, struct nvme_ns, siblings); > } > > The 'NVME_NS_REMOVING' bit is set before list_del_rcu() is called, so it should guard against the issue you mentioned. Looks useless, it is still infinite loop. You can check the workflow for the scenario I mentioned. > > Cheers, > > Hannes _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme
next prev parent reply other threads:[~2021-02-02 1:13 UTC|newest] Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-01-27 10:30 [PATCH v2] nvme-multipath: Early exit if no path is available Daniel Wagner 2021-01-27 10:30 ` Daniel Wagner 2021-01-27 10:34 ` Hannes Reinecke 2021-01-27 10:34 ` Hannes Reinecke 2021-01-27 16:49 ` Christoph Hellwig 2021-01-27 16:49 ` Christoph Hellwig 2021-01-28 1:31 ` Chao Leng 2021-01-28 1:31 ` Chao Leng 2021-01-28 7:58 ` Daniel Wagner 2021-01-28 7:58 ` Daniel Wagner 2021-01-28 9:18 ` Chao Leng 2021-01-28 9:18 ` Chao Leng 2021-01-28 9:23 ` Hannes Reinecke 2021-01-28 9:23 ` Hannes Reinecke 2021-01-29 1:18 ` Chao Leng 2021-01-29 1:18 ` Chao Leng 2021-01-28 9:40 ` Daniel Wagner 2021-01-28 9:40 ` Daniel Wagner 2021-01-29 1:23 ` Chao Leng 2021-01-29 1:23 ` Chao Leng 2021-01-29 1:42 ` Sagi Grimberg 2021-01-29 1:42 ` Sagi Grimberg 2021-01-29 3:07 ` Chao Leng 2021-01-29 3:07 ` Chao Leng 2021-01-29 3:30 ` Sagi Grimberg 2021-01-29 3:30 ` Sagi Grimberg 2021-01-29 3:36 ` Chao Leng 2021-01-29 3:36 ` Chao Leng 2021-01-29 7:06 ` Hannes Reinecke 2021-01-29 7:06 ` Hannes Reinecke 2021-01-29 7:45 ` Chao Leng 2021-01-29 8:33 ` Hannes Reinecke 2021-01-29 8:46 ` Chao Leng 2021-01-29 9:20 ` Hannes Reinecke 2021-02-01 2:16 ` Chao Leng 2021-02-01 2:16 ` Chao Leng 2021-02-01 7:29 ` Hannes Reinecke 2021-02-01 7:29 ` Hannes Reinecke 2021-02-01 8:47 ` Chao Leng 2021-02-01 8:47 ` Chao Leng 2021-02-01 8:57 ` Hannes Reinecke 2021-02-01 8:57 ` Hannes Reinecke 2021-02-01 9:40 ` Chao Leng 2021-02-01 9:40 ` Chao Leng 2021-02-01 10:45 ` Hannes Reinecke 2021-02-01 10:45 ` Hannes Reinecke 2021-02-02 1:12 ` Chao Leng [this message] 2021-02-02 1:12 ` Chao Leng 2021-01-28 1:36 ` Chao Leng 2021-01-28 1:36 ` Chao Leng
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