On Mon, 24 Mar 2008 22:34:56 +0530
"Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote:
> We would like to get notified when we are doing a write on mmap section.
> The changes are needed to handle ENOSPC when writing to an mmap section
> of files with holes.
>
umm,
>
> diff --git a/fs/ext3/file.c b/fs/ext3/file.c
> index acc4913..09e22e4 100644
> --- a/fs/ext3/file.c
> +++ b/fs/ext3/file.c
> @@ -106,6 +106,23 @@ force_commit:
> return ret;
> }
>
> +static struct vm_operations_struct ext3_file_vm_ops = {
> + .fault = filemap_fault,
> + .page_mkwrite = ext3_page_mkwrite,
> +};
> +
> +static int ext3_file_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + struct address_space *mapping = file->f_mapping;
> +
> + if (!mapping->a_ops->readpage)
> + return -ENOEXEC;
> + file_accessed(file);
> + vma->vm_ops = &ext3_file_vm_ops;
> + vma->vm_flags |= VM_CAN_NONLINEAR;
> + return 0;
> +}
> +
> const struct file_operations ext3_file_operations = {
> .llseek = generic_file_llseek,
> .read = do_sync_read,
> @@ -116,7 +133,7 @@ const struct file_operations ext3_file_operations = {
> #ifdef CONFIG_COMPAT
> .compat_ioctl = ext3_compat_ioctl,
> #endif
> - .mmap = generic_file_mmap,
> + .mmap = ext3_file_mmap,
> .open = generic_file_open,
> .release = ext3_release_file,
> .fsync = ext3_sync_file,
> diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c
> index eb95670..2293506 100644
> --- a/fs/ext3/inode.c
> +++ b/fs/ext3/inode.c
> @@ -3306,3 +3306,8 @@ int ext3_change_inode_journal_flag(struct inode *inode, int val)
>
> return err;
> }
> +
> +int ext3_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> +{
> + return block_page_mkwrite(vma, page, ext3_get_block);
> +}
This gets called within the pagefault handler.
And block_page_mkwrite() does lock_page().
But the pagefault handler can be called with a page already locked, from
generic_perform_write().
Nick, why are we not vulnerable to A-A or to AB-BA deadlocks here?
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