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From: "Xie, Huawei" <huawei.xie@intel.com>
To: Pavel Boldin <pboldin@mirantis.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] vhost: Fix `struct file' leakage in `eventfd_link'
Date: Mon, 23 Mar 2015 15:16:40 +0000	[thread overview]
Message-ID: <C37D651A908B024F974696C65296B57B0F3F240D@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <CACf4_B-NTwDd-4NaqxewHSCMLcNPtV0X-4QCWxe=NZqEDN7-3Q@mail.gmail.com>

On 3/23/2015 10:52 PM, Pavel Boldin wrote:


On Mon, Mar 23, 2015 at 4:41 PM, Xie, Huawei <huawei.xie@intel.com<mailto:huawei.xie@intel.com>> wrote:
On 3/23/2015 10:37 PM, Pavel Boldin wrote:


On Mon, Mar 23, 2015 at 4:21 PM, Xie, Huawei <huawei.xie@intel.com<mailto:huawei.xie@intel.com><mailto:huawei.xie@intel.com<mailto:huawei.xie@intel.com>>> wrote:
On 3/23/2015 8:54 PM, Pavel Boldin wrote:
> Due to increased `struct file's reference counter subsequent call
> to `filp_close' does not free the `struct file'. Prepend `fput' call
> to decrease the reference counter.
>
> Signed-off-by: Pavel Boldin <pboldin@mirantis.com<mailto:pboldin@mirantis.com><mailto:pboldin@mirantis.com<mailto:pboldin@mirantis.com>>>
> ---
>  lib/librte_vhost/eventfd_link/eventfd_link.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/lib/librte_vhost/eventfd_link/eventfd_link.c b/lib/librte_vhost/eventfd_link/eventfd_link.c
> index 7755dd6..62c45c8 100644
> --- a/lib/librte_vhost/eventfd_link/eventfd_link.c
> +++ b/lib/librte_vhost/eventfd_link/eventfd_link.c
> @@ -117,6 +117,7 @@ eventfd_link_ioctl(struct file *f, unsigned int ioctl, unsigned long arg)
>                * Release the existing eventfd in the source process
>                */
>               spin_lock(&files->file_lock);
> +             fput(file);
Could we just call atomic_long_dec here?

We can but I don't like breaking encapsulation (which is broken anyway by the code). So, there is a special method and we should use it in my opinion.
it is increased by atomic_long_inc_not_zero so why don't we use the symmetric function?
The code with `atomic_long_inc_not_zero' call is a copy-paste of the `fget' function. If we want to make it clear we should make a separate function and name it so: `fget_from_files'.

I don't understand why there is a (exact?) copy&paste of fget there. :).
Maybe you could post a patchset, first replace the copy/paste with fget and then this patch. It will looks much clearer.
Second thing is: another thread of the same processor can call the `sys_close' on the `fd' and this will dereference counter so `fput' will correctly free the `struct file'. Using `atomic_long_dec' will leak a `struct file' and print a KERN_ERR message by `filp_close'.

So, the common thing is to use appropriate functions and don't reinvent the wheel.

Pavel



Pavel

>               filp_close(file, files);
>               fdt = files_fdtable(files);
>               fdt->fd[eventfd_copy.source_fd] = NULL;

  reply	other threads:[~2015-03-23 15:16 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-23 12:53 Pavel Boldin
2015-03-23 14:21 ` Xie, Huawei
2015-03-23 14:36   ` Pavel Boldin
2015-03-23 14:41     ` Xie, Huawei
2015-03-23 14:51       ` Pavel Boldin
2015-03-23 15:16         ` Xie, Huawei [this message]
2015-03-23 15:22           ` Thomas Monjalon
2015-03-23 15:27           ` Pavel Boldin
2015-03-23 15:36             ` Xie, Huawei
2015-03-23 15:44               ` Pavel Boldin
2015-03-24  6:28 ` Xie, Huawei
2015-03-24 11:10   ` Pavel Boldin
2015-03-24 16:20     ` Xie, Huawei
2015-03-24 20:08       ` Pavel Boldin
2015-03-26  7:53         ` Xie, Huawei
2015-03-27 11:12   ` Thomas Monjalon
2015-03-26  7:56 ` Xie, Huawei
2015-03-26 15:17   ` Pavel Boldin
2015-03-27 11:10   ` Thomas Monjalon
2015-03-27 12:36     ` Pavel Boldin
2015-03-27 13:15       ` Thomas Monjalon
2015-03-26 15:20 ` Xie, Huawei

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