From: Yisheng Xie <xieyisheng1@huawei.com>
To: Vlastimil Babka <vbabka@suse.cz>,
akpm@linux-foundation.org, mhocko@suse.com, mingo@kernel.org,
rientjes@google.com, n-horiguchi@ah.jp.nec.com,
salls@cs.ucsb.edu
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
tanxiaojun@huawei.com, linux-api@vger.kernel.org,
Andi Kleen <ak@linux.intel.com>, Christoph Lameter <cl@linux.com>
Subject: Re: [PATCH RFC v2 4/4] mm/mempolicy: add nodes_empty check in SYSC_migrate_pages
Date: Mon, 6 Nov 2017 09:31:44 +0800 [thread overview]
Message-ID: <bc57f574-92f2-0b69-4717-a1ec7170387c@huawei.com> (raw)
In-Reply-To: <dccbeccc-4155-94a8-0e67-b7c28238896d@suse.cz>
Hi Vlastimil,
On 2017/10/31 17:46, Vlastimil Babka wrote:
> +CC Andi and Christoph
>
> On 10/27/2017 12:14 PM, Yisheng Xie wrote:
>> As manpage of migrate_pages, the errno should be set to EINVAL when none
>> of the specified nodes contain memory. However, when new_nodes is null,
>> i.e. the specified nodes also do not have memory, as the following case:
>>
>> new_nodes = 0;
>> old_nodes = 0xf;
>> ret = migrate_pages(pid, old_nodes, new_nodes, MAX);
>>
>> The ret will be 0 and no errno is set.
>>
>> This patch is to add nodes_empty check to fix above case.
>
> Hmm, I think we have a bigger problem than "empty set is a subset of
> anything" here.
>
> The existing checks are:
>
> task_nodes = cpuset_mems_allowed(task);
> if (!nodes_subset(*new, task_nodes) && !capable(CAP_SYS_NICE)) {
> err = -EPERM;
> goto out_put;
> }
>
> if (!nodes_subset(*new, node_states[N_MEMORY])) {
> err = -EINVAL;
> goto out_put;
> }
>
>
> And manpage says:
>
> EINVAL The value specified by maxnode exceeds a kernel-imposed
> limit. Or, old_nodes or new_nodes specifies one or more node IDs that
> are greater than the maximum supported node
> ID. *Or, none of the node IDs specified by new_nodes are
> on-line and allowed by the process's current cpuset context, or none of
> the specified nodes contain memory.*
>
> EPERM Insufficient privilege (CAP_SYS_NICE) to move pages of the
> process specified by pid, or insufficient privilege (CAP_SYS_NICE) to
> access the specified target nodes.
>
> - it says "none ... are allowed", but checking for subset means we check
> if "all ... are allowed". Shouldn't we be checking for a non-empty
> intersection?
You are absolutely right. To follow the manpage, we should check non-empty
of intersection instead of subset. I meani 1/4 ?
nodes_and(*new, *new, task_nodes);
if (!node_empty(*new) && !capable(CAP_SYS_NICE)) {
err = -EPERM;
goto out_put;
}
nodes_and(*new, *new, node_states[N_MEMORY]);
if (!node_empty(*new)) {
err = -EINVAL;
goto out_put;
}
So finally, we should only migrate the smallest intersection of all the node
set, right?
> - there doesn't seem to be any EINVAL check for "process's current
> cpuset context", there's just an EPERM check for "target process's
> cpuset context".
This also need to be checked as manpage.
Thanks
Yisheng Xie
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next prev parent reply other threads:[~2017-11-06 1:32 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-27 10:14 [PATCH RFC v2 0/4] some fixes and clean up for mempolicy Yisheng Xie
2017-10-27 10:14 ` [PATCH RFC v2 1/4] mm/mempolicy: Fix get_nodes() mask miscalculation Yisheng Xie
2017-10-31 8:34 ` Vlastimil Babka
2017-11-01 9:37 ` Yisheng Xie
2017-10-27 10:14 ` [PATCH RFC v2 2/4] mm/mempolicy: remove redundant check in get_nodes Yisheng Xie
2017-10-31 8:55 ` Vlastimil Babka
2017-10-27 10:14 ` [PATCH RFC v2 3/4] mm/mempolicy: fix the check of nodemask from user Yisheng Xie
2017-10-31 9:30 ` Vlastimil Babka
2017-10-31 11:01 ` Yisheng Xie
2017-10-31 11:28 ` Vlastimil Babka
2017-10-27 10:14 ` [PATCH RFC v2 4/4] mm/mempolicy: add nodes_empty check in SYSC_migrate_pages Yisheng Xie
2017-10-31 9:46 ` Vlastimil Babka
2017-11-06 1:31 ` Yisheng Xie [this message]
2017-11-06 7:39 ` Vlastimil Babka
2017-11-06 15:29 ` Christopher Lameter
2017-11-07 11:23 ` Yisheng Xie
2017-11-07 14:54 ` Christopher Lameter
2017-11-07 15:05 ` Vlastimil Babka
2017-11-07 15:55 ` Christopher Lameter
2017-11-08 1:38 ` Yisheng Xie
2017-11-08 15:02 ` Christopher Lameter
2017-11-09 10:54 ` Yisheng Xie
2017-11-09 15:46 ` Christopher Lameter
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