Messages in this thread | | | From | Evan Green <> | Date | Tue, 16 Nov 2021 12:22:11 -0800 | Subject | Re: [PATCH] PM / hibernate: Fix snapshot partial write lengths |
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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. -Evan
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