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SubjectRe: [PATCH] mm/mempolicy: do not duplicate policy if it is not applicable for set_mempolicy_home_node
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On 2022-12-15 09:49, Michal Hocko wrote:
> On Thu 15-12-22 09:33:54, Mathieu Desnoyers wrote:
>> On 2022-12-15 02:51, Michal Hocko wrote:
> [...]
>>> Btw. looking at the code again it seems rather pointless to duplicate
>>> the policy just to throw it away anyway. A slightly bigger diff but this
>>> looks more reasonable to me. What do you think? I can also send it as a
>>> clean up on top of your fix.
>>
>> I think it would be best if this comes as a cleanup on top of my fix. The
>> diff is larger than the minimal change needed to fix the leak in stable
>> branches.
>>
>> Your approach looks fine, except for the vma_policy(vma) -> old change
>> already spotted by Aneesh.
>
> This shouldn't have any real effect on the functionality. Anyway, here
> is a follow up cleanup:
> ---
> From f3fdb6f65fa3977aab13378b8e299b168719577c Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Thu, 15 Dec 2022 15:41:27 +0100
> Subject: [PATCH] mm/mempolicy: do not duplicate policy if it is not applicable
> for set_mempolicy_home_node
>
> set_mempolicy_home_node tries to duplicate a memory policy before
> checking it whether it is applicable for the operation. There is
> no real reason for doing that and it might actually be a pointless
> memory allocation and deallocation exercise for MPOL_INTERLEAVE.
>
> Not a big problem but we can do better. Simply check the policy before
> acting on it.
>
> Signed-off-by: Michal Hocko <mhocko@suse.com>

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

> ---
> mm/mempolicy.c | 28 ++++++++++++----------------
> 1 file changed, 12 insertions(+), 16 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 02c8a712282f..becf41e10076 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1489,7 +1489,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
> {
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> - struct mempolicy *new;
> + struct mempolicy *new, *old;
> unsigned long vmstart;
> unsigned long vmend;
> unsigned long end;
> @@ -1521,31 +1521,27 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
> return 0;
> mmap_write_lock(mm);
> for_each_vma_range(vmi, vma, end) {
> - vmstart = max(start, vma->vm_start);
> - vmend = min(end, vma->vm_end);
> - new = mpol_dup(vma_policy(vma));
> - if (IS_ERR(new)) {
> - err = PTR_ERR(new);
> - break;
> - }
> - /*
> - * Only update home node if there is an existing vma policy
> - */
> - if (!new)
> - continue;
> -
> /*
> * If any vma in the range got policy other than MPOL_BIND
> * or MPOL_PREFERRED_MANY we return error. We don't reset
> * the home node for vmas we already updated before.
> */
> - if (new->mode != MPOL_BIND && new->mode != MPOL_PREFERRED_MANY) {
> - mpol_put(new);
> + old = vma_policy(vma);
> + if (!old)
> + continue;
> + if (old->mode != MPOL_BIND && old->mode != MPOL_PREFERRED_MANY) {
> err = -EOPNOTSUPP;
> break;
> }
> + new = mpol_dup(old);
> + if (IS_ERR(new)) {
> + err = PTR_ERR(new);
> + break;
> + }
>
> new->home_node = home_node;
> + vmstart = max(start, vma->vm_start);
> + vmend = min(end, vma->vm_end);
> err = mbind_range(mm, vmstart, vmend, new);
> mpol_put(new);
> if (err)

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

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