Re: [PATCH 1/1] infiniband: Remove redundant NULL check before kfree

Re: [PATCH 1/1] infiniband: Remove redundant NULL check before kfree

[Maninder Singh]

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Hello,

>> +			for (i = 0; i < dev->caps.num_ports; i++)
>> +				kfree(dm[i]);
>> 			goto out;
>> 		}
>> 	}
>> --
>> 1.7.9.5
>> 
>
>If you are going to change this, you might as well make it 100% correct:
>
>i—-;
>while (i >= 0)
>	kfree(dm[i]);
>
>Then you don’t have to worry about whether kfree works on NULL, every item you free will be guaranteed to be non-NULL.
Thanks for suggestion :)
Sent new patch with described changes, I was thinking one more thing.

In below code :-
        if (!ibdev->sriov.is_going_down)
            queue_work(ibdev->sriov.demux[i].ud_wq, &dm[i]->work);
        spin_unlock_irqrestore(&ibdev->sriov.going_down_lock, flags);
    }
out:
    kfree(dm);
    return;

dm is freed after queue_work, is it correct to free dm when other dm[i] are allocated ? i did not get it.

Thanks
Maninder
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Re: [PATCH 1/1] infiniband: Remove redundant NULL check before kfree

[Doug Ledford]

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On 07/08/2015 12:23 AM, Maninder Singh wrote:
> Hello,
> 
>>> +			for (i = 0; i < dev->caps.num_ports; i++)
>>> +				kfree(dm[i]);
>>> 			goto out;
>>> 		}
>>> 	}
>>> --
>>> 1.7.9.5
>>>
>>
>> If you are going to change this, you might as well make it 100% correct:
>>
>> i—-;
>> while (i >= 0)
>> 	kfree(dm[i]);
>>
>> Then you don’t have to worry about whether kfree works on NULL, every item you free will be guaranteed to be non-NULL.
> Thanks for suggestion :)
> Sent new patch with described changes, I was thinking one more thing.
> 
> In below code :-
>         if (!ibdev->sriov.is_going_down)
>             queue_work(ibdev->sriov.demux[i].ud_wq, &dm[i]->work);
>         spin_unlock_irqrestore(&ibdev->sriov.going_down_lock, flags);
>     }
> out:
>     kfree(dm);
>     return;
> 
> dm is freed after queue_work, is it correct to free dm when other dm[i] are allocated ? i did not get it.

The dm is just there to give an easy way to refer to a variable number
of work structs.  The flow is supposed to be something like this:

alloc(dm)
for(i=0;i<num_qps;i++)
    dm[i] == alloc(work item);
for(i=0;i<num_qps;i++)
    init dm[i] work item
    queue dm[i] work item
free(dm)

In this scenario, all of the dm[i] items should be queued to delayed
work.  When that work completes, it should then free these structs.  So,
yes, the dm variable itself is just a temporary means of keeping all
those work struct pointers together.  However, your question caused me
to look closely here, and I see that there is a bug.  In particular, if
we check the sriov.is_going_down and as a result *don't* queue a work
item, then we end up leaking that work struct.  In addition, I think
there is room to optimize this routine considerably.  I'll post a patch
for that in a minute.

-- 
Doug Ledford <dledford@redhat.com>
              GPG KeyID: 0E572FDD



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[PATCH 1/1] infiniband: Remove redundant NULL check before kfree

[Maninder Singh]

kfree(NULL) is safe and this check is probably not required

Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
Reviewed-by: Akhilesh Kumar <akhilesh.k@samsung.com>
---
 drivers/infiniband/hw/mlx4/main.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
index 067a691..4e60b39 100644
--- a/drivers/infiniband/hw/mlx4/main.c
+++ b/drivers/infiniband/hw/mlx4/main.c
@@ -2676,10 +2676,8 @@ static void do_slave_init(struct mlx4_ib_dev *ibdev, int slave, int do_init)
 		dm[i] = kmalloc(sizeof (struct mlx4_ib_demux_work), GFP_ATOMIC);
 		if (!dm[i]) {
 			pr_err("failed to allocate memory for tunneling qp update work struct\n");
-			for (i = 0; i < dev->caps.num_ports; i++) {
-				if (dm[i])
-					kfree(dm[i]);
-			}
+			for (i = 0; i < dev->caps.num_ports; i++)
+				kfree(dm[i]);
 			goto out;
 		}
 	}
-- 
1.7.9.5

Re: [PATCH 1/1] infiniband: Remove redundant NULL check before kfree

[Doug Ledford]

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> On Jun 26, 2015, at 3:09 AM, Maninder Singh <maninder1.s@samsung.com> wrote:
> 
> kfree(NULL) is safe and this check is probably not required
> 
> Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
> Reviewed-by: Akhilesh Kumar <akhilesh.k@samsung.com>
> ---
> drivers/infiniband/hw/mlx4/main.c |    6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
> index 067a691..4e60b39 100644
> --- a/drivers/infiniband/hw/mlx4/main.c
> +++ b/drivers/infiniband/hw/mlx4/main.c
> @@ -2676,10 +2676,8 @@ static void do_slave_init(struct mlx4_ib_dev *ibdev, int slave, int do_init)
> 		dm[i] = kmalloc(sizeof (struct mlx4_ib_demux_work), GFP_ATOMIC);
> 		if (!dm[i]) {
> 			pr_err("failed to allocate memory for tunneling qp update work struct\n");
> -			for (i = 0; i < dev->caps.num_ports; i++) {
> -				if (dm[i])
> -					kfree(dm[i]);
> -			}
> +			for (i = 0; i < dev->caps.num_ports; i++)
> +				kfree(dm[i]);
> 			goto out;
> 		}
> 	}
> --
> 1.7.9.5
> 

If you are going to change this, you might as well make it 100% correct:

i—-;
while (i >= 0)
	kfree(dm[i]);

Then you don’t have to worry about whether kfree works on NULL, every item you free will be guaranteed to be non-NULL.

—
Doug Ledford <dledford@redhat.com>
	GPG Key ID: 0E572FDD






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Re: [PATCH 1/1] infiniband: Remove redundant NULL check before kfree

[Christoph Lameter]

This is correct as is.

Acked-by: Christoph Lameter <cl@linux.com>