Hi Dan -
On 2018-07-04 at 14:41 Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
[snip]
> diff --git a/fs/dax.c b/fs/dax.c
> index 4de11ed463ce..57ec272038da 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
[snip]
> +bool dax_lock_mapping_entry(struct page *page)
> +{
> + pgoff_t index;
> + struct inode *inode;
> + bool did_lock = false;
> + void *entry = NULL, **slot;
> + struct address_space *mapping;
> +
> + rcu_read_lock();
> + for (;;) {
> + mapping = READ_ONCE(page->mapping);
> +
> + if (!dax_mapping(mapping))
> + break;
> +
> + /*
> + * In the device-dax case there's no need to lock, a
> + * struct dev_pagemap pin is sufficient to keep the
> + * inode alive, and we assume we have dev_pagemap pin
> + * otherwise we would not have a valid pfn_to_page()
> + * translation.
> + */
> + inode = mapping->host;
> + if (S_ISCHR(inode->i_mode)) {
> + did_lock = true;
> + break;
> + }
> +
> + xa_lock_irq(&mapping->i_pages);
> + if (mapping != page->mapping) {
> + xa_unlock_irq(&mapping->i_pages);
> + continue;
> + }
> + index = page->index;
> +
> + entry = __get_unlocked_mapping_entry(mapping, index, &slot,
> + entry_wait_revalidate);
> + if (!entry) {
> + xa_unlock_irq(&mapping->i_pages);
> + break;
> + } else if (IS_ERR(entry)) {
> + WARN_ON_ONCE(PTR_ERR(entry) != -EAGAIN);
> + continue;
In the IS_ERR case, do you need to xa_unlock the mapping? It looks
like you'll deadlock the next time around the loop.
> + }
> + lock_slot(mapping, slot);
> + did_lock = true;
> + xa_unlock_irq(&mapping->i_pages);
> + break;
> + }
> + rcu_read_unlock();
> +
> + return did_lock;
> +}
