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[209.85.166.45]) by smtp.gmail.com with ESMTPSA id c15sm9815491ilq.50.2021.11.30.10.21.45 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Nov 2021 10:21:45 -0800 (PST) Received: by mail-io1-f45.google.com with SMTP id c3so27345706iob.6 for ; Tue, 30 Nov 2021 10:21:45 -0800 (PST) X-Received: by 2002:a6b:d904:: with SMTP id r4mr1204199ioc.52.1638296505145; Tue, 30 Nov 2021 10:21:45 -0800 (PST) MIME-Version: 1.0 References: <20211029122359.1.I1e23f382fbd8beb19fe1c06d70798b292012c57a@changeid> In-Reply-To: From: Evan Green Date: Tue, 30 Nov 2021 09:44:02 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] PM / hibernate: Fix snapshot partial write lengths To: "Rafael J. Wysocki" Cc: Pavel Machek , Len Brown , LKML , Linux PM , Stable Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 30, 2021 at 3:46 AM Rafael J. Wysocki wrote: > > On Mon, Nov 29, 2021 at 5:50 PM Evan Green wrote: > > > > On Wed, Nov 24, 2021 at 4:54 AM Rafael J. Wysocki wrote: > > > > > > On Tue, Nov 16, 2021 at 9:22 PM Evan Green wrote: > > > > > > > > On Tue, Nov 16, 2021 at 9:54 AM Rafael J. Wysocki wrote: > > > > > > > > > > On Mon, Nov 15, 2021 at 6:13 PM Evan Green wrote: > > > > > > > > > > > > Gentle bump. > > > > > > > > > > > > > > > > > > On Fri, Oct 29, 2021 at 12:24 PM Evan Green 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 > > > > > > > --- > > > > > > > > > > > > > > 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. > > Well, you need to point them to the upstream commit to backport. > > In this particular case it would be > > commit 88a5045f176b78c33a269a30a7b146e99c550bd9 (pm-sleep) > Author: Evan Green > Date: Fri Oct 29 12:24:22 2021 -0700 > > PM: hibernate: Fix snapshot partial write lengths > > I'll send an inclusion request for this. I guess it should go into > all of the applicable -stable series, right? Correct. From what I can tell this code and simple_write_to_buffer() haven't changed since its introduction in 2010, so my patch should have had a fixes tag like: Fixes: d3c1b24c50e8 ("PM / Hibernate: Snapshot cleanup") Thanks for doing that Rafael, sorry for flubbing the stable aspect. -Evan