On Wed, Nov 24, 2021 at 4:54 AM Rafael J. Wysocki rafael@kernel.org wrote:
On Tue, Nov 16, 2021 at 9:22 PM Evan Green evgreen@chromium.org wrote:
On Tue, Nov 16, 2021 at 9:54 AM Rafael J. Wysocki rafael@kernel.org wrote:
On Mon, Nov 15, 2021 at 6:13 PM Evan Green evgreen@chromium.org wrote:
Gentle bump.
On Fri, Oct 29, 2021 at 12:24 PM Evan Green evgreen@chromium.org wrote:
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
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 740723bb388524..ad241b4ff64c58 100644 --- a/kernel/power/user.c +++ b/kernel/power/user.c @@ -177,7 +177,7 @@ 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)) {--
Do you actually see this problem in practice?
Yes. I may fire up another thread to explain why I'm stuck doing a partial page write, and how I might be able to stop doing that in the future with some kernel help. But either way, this is a bug.
OK, patch applied as 5.16-rc material.
I guess it should go into -stable kernels too?
Yes, putting it into -stable would make sense also. I should have CCed them originally, doing that now. -Evan