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Message-ID: <c72184d8-693d-43ce-aed9-00a8fc684137@linux.intel.com>
Date:   Fri, 8 Dec 2023 13:47:35 +0800
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Cc:     baolu.lu@linux.intel.com, Kevin Tian <kevin.tian@intel.com>,
        Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Nicolin Chen <nicolinc@nvidia.com>,
        Yi Liu <yi.l.liu@intel.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        iommu@lists.linux.dev, linux-kselftest@vger.kernel.org,
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        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/6] iommufd: Deliver fault messages to user space
Content-Language: en-US
To:     Jason Gunthorpe <jgg@ziepe.ca>,
        Joel Granados <j.granados@samsung.com>
References: <20231026024930.382898-1-baolu.lu@linux.intel.com>
 <20231026024930.382898-5-baolu.lu@linux.intel.com>
 <CGME20231207163412eucas1p2fa912b4923031804c27c764e5c8d67e7@eucas1p2.samsung.com>
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 <20231207171742.GU1489931@ziepe.ca>
From:   Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <20231207171742.GU1489931@ziepe.ca>
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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