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

[Tianjia Zhang]

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 <v...@zeniv.linux.org.uk>
Signed-off-by: Tianjia Zhang <tianjia.zh...@linux.alibaba.com>
---
  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