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
On Mon, Nov 29, 2021 at 08:50:06AM -0800, Evan Green wrote:
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.
<formletter>
This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for how to do this properly.
</formletter>
On Mon, Nov 29, 2021 at 5:50 PM Evan Green evgreen@chromium.org wrote:
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.
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 evgreen@chromium.org 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?
On Tue, Nov 30, 2021 at 3:46 AM Rafael J. Wysocki rafael@kernel.org wrote:
On Mon, Nov 29, 2021 at 5:50 PM Evan Green evgreen@chromium.org wrote:
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.
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 evgreen@chromium.org 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
linux-stable-mirror@lists.linaro.org
-
Evan Green -
Greg KH -
Rafael J. Wysocki