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Subject[PATCH 4.4 62/91] NFS: Directory page cache pages need to be locked when read
Date
From: Trond Myklebust <trondmy@gmail.com>

[ Upstream commit 114de38225d9b300f027e2aec9afbb6e0def154b ]

When a NFS directory page cache page is removed from the page cache,
its contents are freed through a call to nfs_readdir_clear_array().
To prevent the removal of the page cache entry until after we've
finished reading it, we must take the page lock.

Fixes: 11de3b11e08c ("NFS: Fix a memory leak in nfs_readdir")
Cc: stable@vger.kernel.org # v2.6.37+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfs/dir.c | 30 +++++++++++++++++++-----------
1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index e2927aeb092d0..2ac3d2527ad20 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -720,8 +720,6 @@ int nfs_readdir_filler(nfs_readdir_descriptor_t *desc, struct page* page)
static
void cache_page_release(nfs_readdir_descriptor_t *desc)
{
- if (!desc->page->mapping)
- nfs_readdir_clear_array(desc->page);
page_cache_release(desc->page);
desc->page = NULL;
}
@@ -735,19 +733,28 @@ struct page *get_cache_page(nfs_readdir_descriptor_t *desc)

/*
* Returns 0 if desc->dir_cookie was found on page desc->page_index
+ * and locks the page to prevent removal from the page cache.
*/
static
-int find_cache_page(nfs_readdir_descriptor_t *desc)
+int find_and_lock_cache_page(nfs_readdir_descriptor_t *desc)
{
int res;

desc->page = get_cache_page(desc);
if (IS_ERR(desc->page))
return PTR_ERR(desc->page);
-
- res = nfs_readdir_search_array(desc);
+ res = lock_page_killable(desc->page);
if (res != 0)
- cache_page_release(desc);
+ goto error;
+ res = -EAGAIN;
+ if (desc->page->mapping != NULL) {
+ res = nfs_readdir_search_array(desc);
+ if (res == 0)
+ return 0;
+ }
+ unlock_page(desc->page);
+error:
+ cache_page_release(desc);
return res;
}

@@ -762,7 +769,7 @@ int readdir_search_pagecache(nfs_readdir_descriptor_t *desc)
desc->last_cookie = 0;
}
do {
- res = find_cache_page(desc);
+ res = find_and_lock_cache_page(desc);
} while (res == -EAGAIN);
return res;
}
@@ -807,7 +814,6 @@ int nfs_do_filldir(nfs_readdir_descriptor_t *desc)

nfs_readdir_release_array(desc->page);
out:
- cache_page_release(desc);
dfprintk(DIRCACHE, "NFS: nfs_do_filldir() filling ended @ cookie %Lu; returning = %d\n",
(unsigned long long)*desc->dir_cookie, res);
return res;
@@ -853,13 +859,13 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc)

status = nfs_do_filldir(desc);

+ out_release:
+ nfs_readdir_clear_array(desc->page);
+ cache_page_release(desc);
out:
dfprintk(DIRCACHE, "NFS: %s: returns %d\n",
__func__, status);
return status;
- out_release:
- cache_page_release(desc);
- goto out;
}

/* The file offset position represents the dirent entry number. A
@@ -925,6 +931,8 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
break;

res = nfs_do_filldir(desc);
+ unlock_page(desc->page);
+ cache_page_release(desc);
if (res < 0)
break;
} while (!desc->eof);
--
2.20.1


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