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    SubjectRe: [PATCH v4] mtd: Do not corrupt backing device of device node inode
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    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
    differently?

    > @@ -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
    David.Woodhouse@intel.com Intel Corporation



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