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Subject[PATCH, RESEND] xen: allocate gntdev_copy_batch dynamically
Date
struct gntdev_copy_batch is arguably too large to fit on the kernel stack,
and we get a warning about the stack usage in gntdev_ioctl_grant_copy:

drivers/xen/gntdev.c:949:1: error: the frame size of 1240 bytes is larger than 1024 bytes

This changes the code to us a dynamic allocation instead.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: a4cdb556cae0 ("xen/gntdev: add ioctl for grant copy")
---
drivers/xen/gntdev.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)

I sent this in January, Boris sent an almost identical patch
as http://www.gossamer-threads.com/lists/xen/devel/414056
but the bug remains present in mainline and linux-next as of
Feb 25.

Could you apply one of the patches before the bug makes it
into v4.5?

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index dc495383ad73..cc753b3a7154 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -915,15 +915,16 @@ static int gntdev_grant_copy_seg(struct gntdev_copy_batch *batch,
static long gntdev_ioctl_grant_copy(struct gntdev_priv *priv, void __user *u)
{
struct ioctl_gntdev_grant_copy copy;
- struct gntdev_copy_batch batch;
+ struct gntdev_copy_batch *batch;
unsigned int i;
int ret = 0;

if (copy_from_user(&copy, u, sizeof(copy)))
return -EFAULT;

- batch.nr_ops = 0;
- batch.nr_pages = 0;
+ batch = kzalloc(sizeof(*batch), GFP_KERNEL);
+ if (!batch)
+ return -ENOMEM;

for (i = 0; i < copy.count; i++) {
struct gntdev_grant_copy_segment seg;
@@ -933,18 +934,20 @@ static long gntdev_ioctl_grant_copy(struct gntdev_priv *priv, void __user *u)
goto out;
}

- ret = gntdev_grant_copy_seg(&batch, &seg, &copy.segments[i].status);
+ ret = gntdev_grant_copy_seg(batch, &seg, &copy.segments[i].status);
if (ret < 0)
goto out;

cond_resched();
}
- if (batch.nr_ops)
- ret = gntdev_copy(&batch);
+ if (batch->nr_ops)
+ ret = gntdev_copy(batch);
+ kfree(batch);
return ret;

out:
- gntdev_put_pages(&batch);
+ gntdev_put_pages(batch);
+ kfree(batch);
return ret;
}

--
2.7.0
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