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SubjectRe: [PATCH v4] mtd: Do not corrupt backing device of device node inode
On Wed, 2010-05-05 at 18:40 +0300, Kirill A. Shutemov wrote:
> We cannot modify file->f_mapping->backing_dev_info, because it will corrupt
> backing device of device node inode, since file->f_mapping is equal to
> inode->i_mapping (see __dentry_open() in fs/open.c).
> Let's introduce separate inode for MTD device with appropriate backing
> device.

I hate the fact that we have to do this -- is it really the only option?

Is it _just_ for the backing_device_info? Can't that be done

> @@ -85,11 +88,27 @@ static int mtd_open(struct inode *inode, struct file *file)
> goto out;
> }
> - if (mtd->backing_dev_info)
> - file->f_mapping->backing_dev_info = mtd->backing_dev_info;
> + if (!mtd->inode) {
> + mtd->inode = new_inode(mtd_inode_mnt->mnt_sb);

I believe that would be a race condition, if it wasn't for the BKL.

And what happens when you close the chardevice and call iput() on the
inode so it's destroyed, and then you re-open the device? You never set
mtd->inode = NULL, so won't it now try to igrab a stale pointer?

You won't have seen this in your testing unless you made it prune the
icache between the close and open calls.

David Woodhouse Open Source Technology Centre Intel Corporation

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