linux-kernel - Re: [PATCH] PM / hibernate: Fix snapshot partial write lengths

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Message-ID: <CAE=gft4MRvq-VCBW4EX4dGfPi4s7Lco8h6Z_ejRH5A1e-K2-yA@mail.gmail.com>
Date:   Mon, 15 Nov 2021 09:12:47 -0800
From:   Evan Green <evgreen@...omium.org>
To:     Pavel Machek <pavel@....cz>,
        "Rafael J . Wysocki" <rafael@...nel.org>
Cc:     Len Brown <len.brown@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-pm@...r.kernel.org
Subject: Re: [PATCH] PM / hibernate: Fix snapshot partial write lengths

Gentle bump.


On Fri, Oct 29, 2021 at 12:24 PM Evan Green <evgreen@...omium.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@...omium.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)) {
> --
> 2.31.0
>