From: Chao Leng <lengchao@huawei.com> To: 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>, Hannes Reinecke <hare@suse.de>, Keith Busch <kbusch@kernel.org>, Christoph Hellwig <hch@lst.de> Subject: Re: [PATCH v2] nvme-multipath: Early exit if no path is available Date: Fri, 29 Jan 2021 11:36:08 +0800 [thread overview] Message-ID: <a3c64c60-13f3-1b99-47bc-05ebfefed343@huawei.com> (raw) In-Reply-To: <dbc39e56-b2bd-a82e-499a-5032c9716855@grimberg.me> On 2021/1/29 11:30, Sagi Grimberg wrote: > >>>>> You can't see exactly where it dies but I followed the assembly to >>>>> nvme_round_robin_path(). Maybe it's not the initial nvme_next_ns(head, >>>>> old) which returns NULL but nvme_next_ns() is returning NULL eventually >>>>> (list_next_or_null_rcu()). >>>> So there is other bug cause nvme_next_ns abormal. >>>> I review the code about head->list and head->current_path, I find 2 bugs >>>> may cause the bug: >>>> First, I already send the patch. see: >>>> https://lore.kernel.org/linux-nvme/20210128033351.22116-1-lengchao@huawei.com/ >>>> Second, in nvme_ns_remove, list_del_rcu is before >>>> nvme_mpath_clear_current_path. This may cause "old" is deleted from the >>>> "head", but still use "old". I'm not sure there's any other >>>> consideration here, I will check it and try to fix it. >>> >>> The reason why we first remove from head->list and only then clear >>> current_path is because the other way around there is no way >>> to guarantee that that the ns won't be assigned as current_path >>> again (because it is in head->list). >> ok, I see. >>> >>> nvme_ns_remove fences continue of deletion of the ns by synchronizing >>> the srcu such that for sure the current_path clearance is visible. >> The list will be like this: >> head->next = ns1; >> ns1->next = head; >> old->next = ns1; >> This may cause infinite loop in nvme_round_robin_path. >> for (ns = nvme_next_ns(head, old); >> ns != old; >> ns = nvme_next_ns(head, ns)) >> The ns will always be ns1, and then infinite loop. > > Who is being removed? I'm not following The "old" is being removed path. Daniel Wagner report crash like this: head->next = head; old->next = head; So nvme_next_ns(head, old) will return NULL, and then crash. Although check ns can avoid crash, but can not avoid infinite loop. Similar reason, The list will be like this: head->next = ns1; ns1->next = head; old->next = ns1; ns1 is other path. > .
WARNING: multiple messages have this Message-ID (diff)
From: Chao Leng <lengchao@huawei.com> To: Sagi Grimberg <sagi@grimberg.me>, Daniel Wagner <dwagner@suse.de> Cc: linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, Jens Axboe <axboe@fb.com>, Hannes Reinecke <hare@suse.de>, Keith Busch <kbusch@kernel.org>, Christoph Hellwig <hch@lst.de> Subject: Re: [PATCH v2] nvme-multipath: Early exit if no path is available Date: Fri, 29 Jan 2021 11:36:08 +0800 [thread overview] Message-ID: <a3c64c60-13f3-1b99-47bc-05ebfefed343@huawei.com> (raw) In-Reply-To: <dbc39e56-b2bd-a82e-499a-5032c9716855@grimberg.me> On 2021/1/29 11:30, Sagi Grimberg wrote: > >>>>> You can't see exactly where it dies but I followed the assembly to >>>>> nvme_round_robin_path(). Maybe it's not the initial nvme_next_ns(head, >>>>> old) which returns NULL but nvme_next_ns() is returning NULL eventually >>>>> (list_next_or_null_rcu()). >>>> So there is other bug cause nvme_next_ns abormal. >>>> I review the code about head->list and head->current_path, I find 2 bugs >>>> may cause the bug: >>>> First, I already send the patch. see: >>>> https://lore.kernel.org/linux-nvme/20210128033351.22116-1-lengchao@huawei.com/ >>>> Second, in nvme_ns_remove, list_del_rcu is before >>>> nvme_mpath_clear_current_path. This may cause "old" is deleted from the >>>> "head", but still use "old". I'm not sure there's any other >>>> consideration here, I will check it and try to fix it. >>> >>> The reason why we first remove from head->list and only then clear >>> current_path is because the other way around there is no way >>> to guarantee that that the ns won't be assigned as current_path >>> again (because it is in head->list). >> ok, I see. >>> >>> nvme_ns_remove fences continue of deletion of the ns by synchronizing >>> the srcu such that for sure the current_path clearance is visible. >> The list will be like this: >> head->next = ns1; >> ns1->next = head; >> old->next = ns1; >> This may cause infinite loop in nvme_round_robin_path. >> for (ns = nvme_next_ns(head, old); >> ns != old; >> ns = nvme_next_ns(head, ns)) >> The ns will always be ns1, and then infinite loop. > > Who is being removed? I'm not following The "old" is being removed path. Daniel Wagner report crash like this: head->next = head; old->next = head; So nvme_next_ns(head, old) will return NULL, and then crash. Although check ns can avoid crash, but can not avoid infinite loop. Similar reason, The list will be like this: head->next = ns1; ns1->next = head; old->next = ns1; ns1 is other path. > . _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme
next prev parent reply other threads:[~2021-01-29 3:37 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 [this message] 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 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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