[PATCH AUTOSEL 4.4 7/9] PM: hibernate: Fix snapshot partial write lengths

Sasha Levin
2021-11-30T15:11:14Z

From: Evan Green <evgreen@chromium.org>

[ Upstream commit 88a5045f176b78c33a269a30a7b146e99c550bd9 ]

snapshot_write() is inappropriately limiting the amount of data that can
be written in cases where a partial page has already been written. For
example, one would expect to be able to write 1 byte, then 4095 bytes to
the snapshot device, and have both of those complete fully (since now
we're aligned to a page again). But what ends up happening is we write 1
byte, then 4094/4095 bytes complete successfully.

The reason is that simple_write_to_buffer()'s second argument is the
total size of the buffer, not the size of the buffer minus the offset.
Since simple_write_to_buffer() accounts for the offset in its
implementation, snapshot_write() can just pass the full page size
directly down.

Signed-off-by: Evan Green <evgreen@chromium.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/power/user.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/power/user.c b/kernel/power/user.c
index f83c1876b39c0..67659e507747e 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -181,7 +181,7 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
if (res <= 0)
goto unlock;
} else {
- res = PAGE_SIZE - pg_offp;
+ res = PAGE_SIZE;
}

if (!data_of(data->handle)) {
--
2.33.0