From: Sagi Grimberg <sagi@grimberg.me>
To: Chao Leng <lengchao@huawei.com>, 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: Thu, 28 Jan 2021 19:30:07 -0800 [thread overview]
Message-ID: <dbc39e56-b2bd-a82e-499a-5032c9716855@grimberg.me> (raw)
In-Reply-To: <59cd053e-46cb-0235-141f-4ce919c93f48@huawei.com>
>>>> 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
next prev parent reply other threads:[~2021-01-29 3:30 UTC|newest]
Thread overview: 23+ 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 10:34 ` Hannes Reinecke
2021-01-27 16:49 ` Christoph Hellwig
2021-01-28 1:31 ` Chao Leng
2021-01-28 7:58 ` Daniel Wagner
2021-01-28 9:18 ` Chao Leng
2021-01-28 9:23 ` Hannes Reinecke
2021-01-29 1:18 ` Chao Leng
2021-01-28 9:40 ` Daniel Wagner
2021-01-29 1:23 ` Chao Leng
2021-01-29 1:42 ` Sagi Grimberg
2021-01-29 3:07 ` Chao Leng
2021-01-29 3:30 ` Sagi Grimberg [this message]
2021-01-29 3:36 ` Chao Leng
2021-01-29 7:06 ` Hannes Reinecke
[not found] ` <81b22bbf-4dd3-6161-e63a-9699690a4e4f@huawei.com>
[not found] ` <715dd943-0587-be08-2840-e0948cf0bc62@suse.de>
[not found] ` <eb131d8f-f009-42e7-105d-58b84060f0dd@huawei.com>
[not found] ` <ac019690-7f02-d28c-ed58-bfc8c1d48879@suse.de>
2021-02-01 2:16 ` Chao Leng
2021-02-01 7:29 ` Hannes Reinecke
2021-02-01 8:47 ` Chao Leng
2021-02-01 8:57 ` Hannes Reinecke
2021-02-01 9:40 ` Chao Leng
2021-02-01 10:45 ` Hannes Reinecke
2021-02-02 1:12 ` Chao Leng
2021-01-28 1:36 ` Chao Leng
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=dbc39e56-b2bd-a82e-499a-5032c9716855@grimberg.me \
--to=sagi@grimberg.me \
--cc=axboe@fb.com \
--cc=dwagner@suse.de \
--cc=hare@suse.de \
--cc=hch@lst.de \
--cc=kbusch@kernel.org \
--cc=lengchao@huawei.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-nvme@lists.infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).