Commit 648a4548 authored by Trond Myklebust's avatar Trond Myklebust
Browse files

NFS: Don't deadlock when cookie hashes collide 



In the very rare case where the readdir reply contains multiple cookies
that map to the same hash value, we can end up deadlocking waiting for a
page lock that we already hold. In this case we should fail the page
lock by using grab_cache_page_nowait().

Signed-off-by: default avatarTrond Myklebust <trond.myklebust@hammerspace.com>
parent a43bf604

fs/nfs/dir.c

+18 −11
Original line number Diff line number Diff line
@@ -381,23 +381,28 @@ static void nfs_readdir_page_unlock_and_put(struct page *page) 
	put_page(page);

}



static struct page *nfs_readdir_page_get_locked(struct address_space *mapping,

						u64 last_cookie,

static void nfs_readdir_page_init_and_validate(struct page *page, u64 cookie,

					       u64 change_attr)

{

	pgoff_t index = nfs_readdir_page_cookie_hash(last_cookie);

	if (PageUptodate(page)) {

		if (nfs_readdir_page_validate(page, cookie, change_attr))

			return;

		nfs_readdir_clear_array(page);

	}

	nfs_readdir_page_init_array(page, cookie, change_attr);

	SetPageUptodate(page);

}



static struct page *nfs_readdir_page_get_locked(struct address_space *mapping,

						u64 cookie, u64 change_attr)

{

	pgoff_t index = nfs_readdir_page_cookie_hash(cookie);

	struct page *page;



	page = grab_cache_page(mapping, index);

	if (!page)

		return NULL;

	if (PageUptodate(page)) {

		if (nfs_readdir_page_validate(page, last_cookie, change_attr))

			return page;

		nfs_readdir_clear_array(page);

	}

	nfs_readdir_page_init_array(page, last_cookie, change_attr);

	SetPageUptodate(page);

	nfs_readdir_page_init_and_validate(page, cookie, change_attr);

	return page;

}
@@ -435,11 +440,13 @@ static void nfs_readdir_page_set_eof(struct page *page) 
static struct page *nfs_readdir_page_get_next(struct address_space *mapping,

					      u64 cookie, u64 change_attr)

{

	pgoff_t index = nfs_readdir_page_cookie_hash(cookie);

	struct page *page;



	page = nfs_readdir_page_get_locked(mapping, cookie, change_attr);

	page = grab_cache_page_nowait(mapping, index);

	if (!page)

		return NULL;

	nfs_readdir_page_init_and_validate(page, cookie, change_attr);

	if (nfs_readdir_page_last_cookie(page) != cookie)

		nfs_readdir_page_reinit_array(page, cookie, change_attr);

	return page;