PM: hibernate: Clean up sync_read handling in snapshot_write_next()

commit d08970df1980476f27936e24d452550f3e9e92e1 upstream.

In snapshot_write_next(), sync_read is set and unset in three different
spots unnecessiarly. As a result there is a subtle bug where the first
page after the meta data has been loaded unconditionally sets sync_read
to 0. If this first PFN was actually a highmem page, then the returned
buffer will be the global "buffer," and the page needs to be loaded
synchronously.

That is, I'm not sure we can always assume the following to be safe:

	handle->buffer = get_buffer(&orig_bm, &ca);
	handle->sync_read = 0;

Because get_buffer() can call get_highmem_page_buffer() which can
return 'buffer'.

The easiest way to address this is just set sync_read before
snapshot_write_next() returns if handle->buffer == buffer.

Signed-off-by: Brian Geffon <bgeffon@google.com>
Fixes: 8357376d3df2 ("[PATCH] swsusp: Improve handling of highmem")
Cc: All applicable <stable@vger.kernel.org>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 6c5cbac2f6612424d4bfec0b6ad0c67eb2371bd4..336e56e97b8d5fa1eb078472e4ef5f1a893f8bb7 100644 (file)
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -2592,8 +2592,6 @@ int snapshot_write_next(struct snapshot_handle *handle)
        if (handle->cur > 1 && handle->cur > nr_meta_pages + nr_copy_pages)
                return 0;
 
-       handle->sync_read = 1;
-
        if (!handle->cur) {
                if (!buffer)
                        /* This makes the buffer be freed by swsusp_free() */
@@ -2634,7 +2632,6 @@ int snapshot_write_next(struct snapshot_handle *handle)
                        memory_bm_position_reset(&orig_bm);
                        restore_pblist = NULL;
                        handle->buffer = get_buffer(&orig_bm, &ca);
-                       handle->sync_read = 0;
                        if (IS_ERR(handle->buffer))
                                return PTR_ERR(handle->buffer);
                }
@@ -2646,9 +2643,8 @@ int snapshot_write_next(struct snapshot_handle *handle)
                handle->buffer = get_buffer(&orig_bm, &ca);
                if (IS_ERR(handle->buffer))
                        return PTR_ERR(handle->buffer);
-               if (handle->buffer != buffer)
-                       handle->sync_read = 0;
        }
+       handle->sync_read = (handle->buffer == buffer);
        handle->cur++;
        return PAGE_SIZE;
 }