Re: [PATCH] fs: fix i_writecount on shmem and friends

From: Al Viro
Date: Thu Mar 13 2014 - 00:29:59 EST


On Thu, Mar 13, 2014 at 03:08:00PM +1100, NeilBrown wrote:
> + inode = mddev->bitmap_info.file->f_mapping->host;
> + if (!S_ISREG(inode->i_mode)) {
> + printk(KERN_ERR "%s: error: bitmap file must be a regular file\n",
> + mdname(mddev));
> + fput(mddev->bitmap_info.file);
> + mddev->bitmap_info.file = NULL;
> + return -EBADF;
> + }
> + if (atomic_read(&inode->i_writecount) != 1) {

Umm... I think you ought to check more than that. At the very least you
want to check that you have it opened for write - you don't want e.g.
a filesystem containing that puppy remounted r/o under you. Another thing
is, what happens if it's not a buffer cache backed one? Hell, what happens
if it's a file on NFS? You are relying on bmap() working, right? So it
looks like you ought to check if ->bmap() is there. And I really wonder
how well does it play with journalling fs...
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