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Message-ID: <c72184d8-693d-43ce-aed9-00a8fc684137@linux.intel.com>
Date: Fri, 8 Dec 2023 13:47:35 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>,
Joel Granados <j.granados@...sung.com>
Cc: baolu.lu@...ux.intel.com, Kevin Tian <kevin.tian@...el.com>,
Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
Robin Murphy <robin.murphy@....com>,
Jean-Philippe Brucker <jean-philippe@...aro.org>,
Nicolin Chen <nicolinc@...dia.com>,
Yi Liu <yi.l.liu@...el.com>,
Jacob Pan <jacob.jun.pan@...ux.intel.com>,
iommu@...ts.linux.dev, linux-kselftest@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] iommufd: Deliver fault messages to user space
On 12/8/23 1:17 AM, Jason Gunthorpe wrote:
> On Thu, Dec 07, 2023 at 05:34:10PM +0100, Joel Granados wrote:
>>> @@ -58,6 +255,8 @@ static void hw_pagetable_fault_free(struct hw_pgtable_fault *fault)
>>> WARN_ON(!list_empty(&fault->deliver));
>>> WARN_ON(!list_empty(&fault->response));
>>>
>>> + fput(fault->fault_file);
>>> + put_unused_fd(fault->fault_fd);
>> I have resolved this in a naive way by just not calling the
>> put_unused_fd function.
> That is correct.
>
> put_unused_fd() should only be called on error paths prior to the
> syscall return.
>
> The design of a FD must follow this pattern
>
> syscall():
> fdno = get_unused_fd_flags(O_CLOEXEC);
> filep = [..]
>
> // syscall MUST succeed after this statement:
> fd_install(fdno, filep);
> return 0;
>
> err:
> put_unused_fd(fdno)
> return -ERRNO
Yes. Agreed.
>
> Also the refcounting looks a little strange, the filep reference is
> consumed by fd_install, so what is that fput pairing with in fault_free?
fput() pairs with get_unused_fd_flags()? fd_install() does not seem to
increase any reference.
Best regards,
baolu
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