>>> On 04.11.14 at 12:43, <"jack@xxxxxxx".non-mime.internet> wrote:
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -743,10 +743,13 @@ EXPORT_SYMBOL(truncate_setsize);
> * changed.
> *
> * The function must be called after i_size is updated so that page fault
> - * coming after we unlock the page will already see the new i_size.
> - * The function must be called while we still hold i_mutex - this not only
> - * makes sure i_size is stable but also that userspace cannot observe new
> - * i_size value before we are prepared to store mmap writes at new inode size.
> + * coming after we unlock the page will already see the new i_size. The caller
> + * must make sure (generally by holding i_mutex but e.g. XFS uses its private
> + * lock) i_size cannot change from the new value while we are called. It must
> + * also make sure userspace cannot observe new i_size value before we are
> + * prepared to store mmap writes upto new inode size (otherwise userspace could
> + * think it stored data via mmap within i_size but they would get zeroed due to
> + * writeback & reclaim because they have no backing blocks).
> */
> void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to)
> {
May I suggest that the comment preceding truncate_setsize() also be
updated/removed?
Jan
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