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Commit 466bd31b authored by Sachin Prabhu's avatar Sachin Prabhu Committed by Steve French
Browse files

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: default avatarSachin Prabhu <sprabhu@redhat.com>
Reviewed-by: default avatarJeff Layton <jlayton@redhat.com>
Signed-off-by: default avatarSteve French <smfrench@gmail.com>
parent a9e9b7bc

fs/cifs/file.c

+7 −3
Original line number Diff line number Diff line
@@ -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