Messages in this thread | | | Subject | Re: [PATCH v2] nvme-multipath: Early exit if no path is available | From | Chao Leng <> | Date | Fri, 29 Jan 2021 09:18:10 +0800 |
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On 2021/1/28 17:23, Hannes Reinecke wrote: > On 1/28/21 10:18 AM, Chao Leng wrote: >> >> >> On 2021/1/28 15:58, Daniel Wagner wrote: >>> On Thu, Jan 28, 2021 at 09:31:30AM +0800, Chao Leng wrote: >>>>> --- a/drivers/nvme/host/multipath.c >>>>> +++ b/drivers/nvme/host/multipath.c >>>>> @@ -221,7 +221,7 @@ static struct nvme_ns *nvme_round_robin_path(struct nvme_ns_head *head, >>>>> } >>>>> for (ns = nvme_next_ns(head, old); >>>>> - ns != old; >>>>> + ns && ns != old; >>>> nvme_round_robin_path just be called when !"old". >>>> nvme_next_ns should not return NULL when !"old". >>>> It seems unnecessary to add checking "ns". >>> >>> The problem is when we enter nvme_round_robin_path() and there is no >>> path available. In this case the initialization ns = nvme_next_ns(head, >>> old) could return a NULL pointer."old" should not be NULL, so there is at least one path that is "old". >> It is impossible to return NULL for nvme_next_ns(head, old). > > No. list_next_or_null_rcu()/list_first_or_null_rcu() will return NULL when then end of the list is reached. Although list_next_or_null_rcu()/list_first_or_null_rcu() may return NULL, but nvme_next_ns(head, old) assume that the "old" is in the "head", so nvme_next_ns(head, old) should not return NULL. If the "old" is not in the "head", nvme_next_ns(head, old) will run abnormal. So there is other bug which cause nvme_next_ns(head, old).
I review the code about head->list and head->current_path, I find 2 bugs may cause nvme_next_ns(head, old) abnormal: 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. > > Cheers, > > Hannes
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