linux-kernel - RE: [PATCH 1/5] hisi_acc_vfio

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Date:   Wed, 21 Sep 2022 07:27:06 +0000
From:   Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To:     liulongfang <liulongfang@...wei.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Alex Williamson <alex.williamson@...hat.com>
CC:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxarm@...neuler.org" <linuxarm@...neuler.org>
Subject: RE: [PATCH 1/5] hisi_acc_vfio_pci: Fixes a memory leak bug



> -----Original Message-----
> From: liulongfang
> Sent: 21 September 2022 04:13
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>;
> Jason Gunthorpe <jgg@...dia.com>; Alex Williamson
> <alex.williamson@...hat.com>
> Cc: cohuck@...hat.com; linux-kernel@...r.kernel.org;
> linuxarm@...neuler.org
> Subject: Re: [PATCH 1/5] hisi_acc_vfio_pci: Fixes a memory leak bug
> 
> On 2022/9/21 1:03, Shameerali Kolothum Thodi wrote:
> >
> >
> >> -----Original Message-----
> >> From: Jason Gunthorpe [mailto:jgg@...dia.com]
> >> Sent: 20 September 2022 17:38
> >> To: Alex Williamson <alex.williamson@...hat.com>
> >> Cc: liulongfang <liulongfang@...wei.com>; Shameerali Kolothum Thodi
> >> <shameerali.kolothum.thodi@...wei.com>; cohuck@...hat.com;
> >> linux-kernel@...r.kernel.org; linuxarm@...neuler.org
> >> Subject: Re: [PATCH 1/5] hisi_acc_vfio_pci: Fixes a memory leak bug
> >>
> >> On Tue, Sep 20, 2022 at 10:34:43AM -0600, Alex Williamson wrote:
> >>> On Thu, 15 Sep 2022 09:31:53 +0800
> >>> Longfang Liu <liulongfang@...wei.com> wrote:
> >>>
> >>>> During the stop copy phase of live migration, the driver allocates a
> >>>> memory for the migrated data to save the data.
> >>>>
> >>>> When an exception occurs when the driver reads device data, the
> >>>> driver will report an error to qemu and exit the current migration state.
> >>>> But this memory is not released, which will lead to a memory leak
> >>>> problem.
> >>
> >> Why isn't it released? The fput() releases it:
> >>
> >> static int hisi_acc_vf_release_file(struct inode *inode, struct file *filp) {
> >> 	struct hisi_acc_vf_migration_file *migf = filp->private_data;
> >>
> >> 	hisi_acc_vf_disable_fd(migf);
> >> 	mutex_destroy(&migf->lock);
> >> 	kfree(migf);
> >>         ^^^^^^^^^^
> >>
> >> This patch looks wrong to me.
> >
> > That's right. Missed that. Sorry of the oversight.
> >
> Yes, fput will call release in ops of file, here will call hisi_acc_vf_release_file
> to complete the release operation of migf, so this patch is unnecessary.
> 
> But there is another place that needs to be modified:
> hisi_acc_vf_disable_fd in hisi_acc_vf_disable_fds is not needed,
> because it will have an fput next. Is this correct?

I don't think that is correct either. fput() decrements ref count and 
will only call release() if the count is zero. We have an explicit get_file()
for the hisi_acc_vf_disable_fds(). Isn't it?

Thanks,
Shameer


 
> > Thanks,
> > Shameer
> >
> > .
> Thanks,
> Longfang.
> >