Messages in this thread |  | | Subject | Re: [PATCH v9 09/22] s390: vfio-ap: register matrix device with VFIO mdev framework | From | Tony Krowiak <> | Date | Fri, 17 Aug 2018 15:02:02 -0400 |
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On 08/17/2018 04:43 AM, Cornelia Huck wrote: > On Thu, 16 Aug 2018 12:24:16 -0400 > Tony Krowiak <akrowiak@linux.ibm.com> wrote: > >> On 08/14/2018 07:19 AM, Cornelia Huck wrote: >>> On Mon, 13 Aug 2018 17:48:06 -0400 >>> Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote: >>>> +static int vfio_ap_mdev_create(struct kobject *kobj, struct mdev_device *mdev) >>>> +{ >>>> + struct ap_matrix_mdev *matrix_mdev; >>>> + >>>> + matrix_mdev = kzalloc(sizeof(*matrix_mdev), GFP_KERNEL); >>>> + if (!matrix_mdev) >>>> + return -ENOMEM; >>>> + >>>> + matrix_mdev->name = dev_name(mdev_dev(mdev)); >>>> + vfio_ap_matrix_init(&matrix_dev.info, &matrix_mdev->matrix); >>>> + mdev_set_drvdata(mdev, matrix_mdev); >>>> + >>>> + if (atomic_dec_if_positive(&matrix_dev.available_instances) < 0) { >>>> + kfree(matrix_mdev); >>>> + return -EPERM; >>>> + } >>> Maybe move this check to the top of the function? >> Please ignore my previous response to your comment. I can't move the call to >> atomic_dec_if_positive() to the top of the function because it >> decrements the >> available_instances and if the kzalloc() of matrix_mdev fails, then the >> value >> would have to then be incremented to remain valid. What I can do is this: >> >> 1. Check the value of available_instances using atomic_read() at the top of >> the function and if it is zero, return an error. >> >> 2. Replace the call to atomic_dec_if_positive() with a call to atomic_dec() >> to decrement the available_instances. >> >> I agree that it makes sense to return before attempting to allocate the >> matrix_mdev if available_instances is zero. > Wouldn't that be racy, though? > > I don't think re-incrementing the counter is too bad, and it's > certainly better than going through allocation/freeing of structures.
I'll make it happen.
> >>> >>>> + >>>> + mutex_lock(&matrix_dev.lock); >>>> + list_add(&matrix_mdev->list, &matrix_dev.mdev_list); >>>> + mutex_unlock(&matrix_dev.lock); >>>> + >>>> + return 0; >>>> +} >>
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