linux-kernel - Re: [PATCH v1 1/2] iommufd/fault: Fix out_fput in iommufd_fault

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Message-ID: <a6487e28-787a-4c9a-9dcb-15d92d0f6b3d@intel.com>
Date: Tue, 3 Dec 2024 17:52:42 +0800
From: Yi Liu <yi.l.liu@...el.com>
To: Nicolin Chen <nicolinc@...dia.com>, <jgg@...dia.com>,
	<kevin.tian@...el.com>
CC: <baolu.lu@...ux.intel.com>, <iommu@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
	<shuah@...nel.org>
Subject: Re: [PATCH v1 1/2] iommufd/fault: Fix out_fput in
 iommufd_fault_alloc()

On 2024/12/3 16:02, Nicolin Chen wrote:
> As fput() calls the file->f_op->release op, where fault obj and ictx are
> getting released, there is no need to release these two after fput() one
> more time, which would result in imbalanced refcounts:
>    refcount_t: decrement hit 0; leaking memory.
>    WARNING: CPU: 48 PID: 2369 at lib/refcount.c:31 refcount_warn_saturate+0x60/0x230
>    Call trace:
>     refcount_warn_saturate+0x60/0x230 (P)
>     refcount_warn_saturate+0x60/0x230 (L)
>     iommufd_fault_fops_release+0x9c/0xe0 [iommufd]
>    ...
>    VFS: Close: file count is 0 (f_op=iommufd_fops [iommufd])
>    WARNING: CPU: 48 PID: 2369 at fs/open.c:1507 filp_flush+0x3c/0xf0
>    Call trace:
>     filp_flush+0x3c/0xf0 (P)
>     filp_flush+0x3c/0xf0 (L)
>     __arm64_sys_close+0x34/0x98
>    ...
>    imbalanced put on file reference count
>    WARNING: CPU: 48 PID: 2369 at fs/file.c:74 __file_ref_put+0x100/0x138
>    Call trace:
>     __file_ref_put+0x100/0x138 (P)
>     __file_ref_put+0x100/0x138 (L)
>     __fput_sync+0x4c/0xd0
> 
> Drop those two lines to fix the warnings above.
> 
> Fixes: 07838f7fd529 ("iommufd: Add iommufd fault object")
> Cc: stable@...r.kernel.org
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> ---
>   drivers/iommu/iommufd/fault.c | 2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/fault.c b/drivers/iommu/iommufd/fault.c
> index 053b0e30f55a..1fe804e28a86 100644
> --- a/drivers/iommu/iommufd/fault.c
> +++ b/drivers/iommu/iommufd/fault.c
> @@ -420,8 +420,6 @@ int iommufd_fault_alloc(struct iommufd_ucmd *ucmd)
>   	put_unused_fd(fdno);
>   out_fput:
>   	fput(filep);
> -	refcount_dec(&fault->obj.users);
> -	iommufd_ctx_put(fault->ictx);
>   out_abort:
>   	iommufd_object_abort_and_destroy(ucmd->ictx, &fault->obj);
>   

Reviewed-by: Yi Liu <yi.l.liu@...el.com>

-- 
Regards,
Yi Liu