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SubjectRe: [PATCH] drm: fix i_mapping and f_mapping initialization in drm_open in error path
On Sat 30-03-13 18:26:53, Ilija Hadzic wrote:
> This looks a bit like a hack and it doesn't look right,
> conceptually. If the call fails, it should restore things as if
> nothing has ever happened and overwriting old_mapping is not going to
> do the trick.

OK, I thought this is what the patch does as it falls back to
&inode->i_data which is the default mapping for all inodes or it uses
what used to be in device mapping.

I am obviously not familiar with the drm code but it feels a bit strange
that the device mapping can be different than inode's resp. file's one
and even more confusing that inode and file are saved separately.

> I think the right way to fix it would be to separately store the
> original mapping for filp->f_mapping and inode->i_mapping and restore
> it from their respective temporary variables if drm_open_helper or
> drm_setup fail. Attached is a quick patch to show you
[...]
> @@ -137,6 +139,8 @@ int drm_open(struct inode *inode, struct file *filp)
> if (!dev->open_count++)
> need_setup = 1;
> mutex_lock(&dev->struct_mutex);
> + old_fmapping = filp->f_mapping;
> + old_imapping = inode->i_mapping;

How can file and inode mappings be different?

> old_mapping = dev->dev_mapping;
> if (old_mapping == NULL)
> dev->dev_mapping = &inode->i_data;
> @@ -159,8 +163,8 @@ int drm_open(struct inode *inode, struct file *filp)
>
> err_undo:
> mutex_lock(&dev->struct_mutex);
> - filp->f_mapping = old_mapping;
> - inode->i_mapping = old_mapping;
> + filp->f_mapping = old_fmapping;
> + inode->i_mapping = old_imapping;
> iput(container_of(dev->dev_mapping, struct inode, i_data));
> dev->dev_mapping = old_mapping;
> mutex_unlock(&dev->struct_mutex);
--
1.8.1.5

--
Michal Hocko
SUSE Labs


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