2020-09-20 16:32:36

by Tianjia Zhang

Subject: [PATCH] mm/shmem.c: Fix the missing unaccount on the failed path

In function __shmem_file_setup(), shmem_unacct_size() is forgotten
on the failed path, so add it.

Fixes: 93dec2da7b234 ("... and switch shmem_file_setup() to alloc_file_pseudo()")
Cc: Al Viro <[email protected]>
Signed-off-by: Tianjia Zhang <[email protected]>
---
mm/shmem.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 8e2b35ba93ad..591410dc3541 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -4200,8 +4200,10 @@ static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name, l
if (!IS_ERR(res))
res = alloc_file_pseudo(inode, mnt, name, O_RDWR,
&shmem_file_operations);
- if (IS_ERR(res))
+ if (IS_ERR(res)) {
iput(inode);
+ shmem_unacct_size(flags, size);
+ }
return res;
}

--
2.19.1.3.ge56e4f7

2020-09-20 18:53:47

by Hugh Dickins

Subject: Re: [PATCH] mm/shmem.c: Fix the missing unaccount on the failed path

On Mon, 21 Sep 2020, Tianjia Zhang wrote:

> In function __shmem_file_setup(), shmem_unacct_size() is forgotten
> on the failed path, so add it.
>
> Fixes: 93dec2da7b234 ("... and switch shmem_file_setup() to alloc_file_pseudo()")
> Cc: Al Viro <[email protected]>
> Signed-off-by: Tianjia Zhang <[email protected]>
> ---
> mm/shmem.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 8e2b35ba93ad..591410dc3541 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -4200,8 +4200,10 @@ static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name, l
> if (!IS_ERR(res))
> res = alloc_file_pseudo(inode, mnt, name, O_RDWR,
> &shmem_file_operations);
> - if (IS_ERR(res))
> + if (IS_ERR(res)) {
> iput(inode);
> + shmem_unacct_size(flags, size);
> + }
> return res;
> }
>
> --
> 2.19.1.3.ge56e4f7

Looks mistaken to me.

Is this something you noticed by source inspection,
or something you have observed in practice?

I haven't tried exercising this path while injecting errors into
alloc_file_pseudo(); but what I'd expect to happen is that the
iput(inode), which you see already on that error path, will get
to evict the inode, which will entail calling shmem_evict_inode(),
which does that shmem_unacct_size() itself.

Hugh

2020-09-22 08:27:03

by Tianjia Zhang

Subject: Re: [PATCH] mm/shmem.c: Fix the missing unaccount on the failed path

On 9/21/20 2:49 AM, Hugh Dickins wrote:
> On Mon, 21 Sep 2020, Tianjia Zhang wrote:
>
>> In function __shmem_file_setup(), shmem_unacct_size() is forgotten
>> on the failed path, so add it.
>>
>> Fixes: 93dec2da7b234 ("... and switch shmem_file_setup() to alloc_file_pseudo()")
>> Cc: Al Viro <[email protected]>
>> Signed-off-by: Tianjia Zhang <[email protected]>
>> ---
>> mm/shmem.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 8e2b35ba93ad..591410dc3541 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -4200,8 +4200,10 @@ static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name, l
>> if (!IS_ERR(res))
>> res = alloc_file_pseudo(inode, mnt, name, O_RDWR,
>> &shmem_file_operations);
>> - if (IS_ERR(res))
>> + if (IS_ERR(res)) {
>> iput(inode);
>> + shmem_unacct_size(flags, size);
>> + }
>> return res;
>> }
>>
>> --
>> 2.19.1.3.ge56e4f7
>
> Looks mistaken to me.
>
> Is this something you noticed by source inspection,
> or something you have observed in practice?
>
> I haven't tried exercising this path while injecting errors into
> alloc_file_pseudo(); but what I'd expect to happen is that the
> iput(inode), which you see already on that error path, will get
> to evict the inode, which will entail calling shmem_evict_inode(),
> which does that shmem_unacct_size() itself.
>
> Hugh
>

I noticed by looking at the code. you are right, I neglected this point,
thanks for your explanation.

Thanks,
Tianjia