cifs: Avoid calling unlock_page() twice in cifs_readpage() when using fscache

When reading a single page with cifs_readpage(), we make a call to
fscache_read_or_alloc_page() which once done, asynchronously calls
the completion function cifs_readpage_from_fscache_complete(). This
completion function unlocks the page once it has been populated from
cache. The module then attempts to unlock the page a second time in
cifs_readpage() which leads to warning messages.

In case of a successful call to fscache_read_or_alloc_page() we should skip
the second unlock_page() since this will be called by the
cifs_readpage_from_fscache_complete() once the page has been populated by
fscache.

With the modifications to cifs_readpage_worker(), we will need to re-grab the
page lock in cifs_write_begin().

The problem was first noticed when testing new fscache patches for cifs.
https://bugzilla.redhat.com/show_bug.cgi?id=1005737

Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 5f99ee551662..eb955b525e55 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -3419,6 +3419,7 @@ static int cifs_readpage_worker(struct file *file, struct page *page,
 
 io_error:
         kunmap(page);
+        unlock_page(page);
 
 read_complete:
         return rc;
@@ -3443,8 +3444,6 @@ static int cifs_readpage(struct file *file, struct page *page)
 
         rc = cifs_readpage_worker(file, page, &offset);
 
-        unlock_page(page);
-
         free_xid(xid);
         return rc;
 }
@@ -3498,6 +3497,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
                         loff_t pos, unsigned len, unsigned flags,
                         struct page **pagep, void **fsdata)
 {
+        int oncethru = 0;
         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
         loff_t offset = pos & (PAGE_CACHE_SIZE - 1);
         loff_t page_start = pos & PAGE_MASK;
@@ -3507,6 +3507,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
 
         cifs_dbg(FYI, "write_begin from %lld len %d\n", (long long)pos, len);
 
+start:
         page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page) {
                 rc = -ENOMEM;
@@ -3548,13 +3549,16 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
                 }
         }
 
-        if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
+        if ((file->f_flags & O_ACCMODE) != O_WRONLY && !oncethru) {
                 /*
                  * might as well read a page, it is fast enough. If we get
                  * an error, we don't need to return it. cifs_write_end will
                  * do a sync write instead since PG_uptodate isn't set.
                  */
                 cifs_readpage_worker(file, page, &page_start);
+                page_cache_release(page);
+                oncethru = 1;
+                goto start;
         } else {
                 /* we could try using another file handle if there is one -
                    but how would we lock it to prevent close of that handle