On 10/20/2015 04:52 PM, Mike Kravetz wrote:
> if (hole_end > hole_start) {
> struct address_space *mapping = inode->i_mapping;
> + DECLARE_WAIT_QUEUE_HEAD_ONSTACK(hugetlb_falloc_waitq);
> + /*
> + * Page faults on the area to be hole punched must be stopped
> + * during the operation. Initialize struct and have
> + * inode->i_private point to it.
> + */
> + struct hugetlb_falloc hugetlb_falloc = {
> + .waitq = &hugetlb_falloc_waitq,
> + .start = hole_start >> hpage_shift,
> + .end = hole_end >> hpage_shift
> + };
...
> @@ -527,6 +550,12 @@ static long hugetlbfs_punch_hole(struct inode *inode,
> loff_t offset, loff_t len)
> hole_end >> PAGE_SHIFT);
> i_mmap_unlock_write(mapping);
> remove_inode_hugepages(inode, hole_start, hole_end);
> +
> + spin_lock(&inode->i_lock);
> + inode->i_private = NULL;
> + wake_up_all(&hugetlb_falloc_waitq);
> + spin_unlock(&inode->i_lock);
I see the shmem code doing something similar. But, in the end, we're
passing the stack-allocated 'hugetlb_falloc_waitq' over to the page
faulting thread. Is there something subtle that keeps
'hugetlb_falloc_waitq' from becoming invalid while the other task is
sleeping?
That wake_up_all() obviously can't sleep, but it seems like the faulting
thread's finish_wait() *HAS* to run before wake_up_all() can return.
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