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NFS: Don't deadlock when cookie hashes collide

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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: Trond Myklebust <trond.myklebust@hammerspace.com>
This commit is contained in:
Trond Myklebust 2022-03-21 22:27:13 -04:00
parent a43bf60444
commit 648a4548d6
1 changed files with 19 additions and 12 deletions
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31
fs/nfs/dir.c
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@ -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,
u64 change_attr)
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;