* [PATCH] sample: vfio-mdev: avoid deadlock in mdev_access()
@ 2018-07-06 20:50 Alexey Khoroshilov
2018-07-11 19:30 ` Alex Williamson
0 siblings, 1 reply; 2+ messages in thread
From: Alexey Khoroshilov @ 2018-07-06 20:50 UTC (permalink / raw)
To: Gerd Hoffmann, Alex Williamson, Kirti Wankhede
Cc: Alexey Khoroshilov, kvm, linux-kernel, ldv-project
mdev_access() calls mbochs_get_page() with mdev_state->ops_lock held,
while mbochs_get_page() locks the mutex by itself.
It leads to unavoidable deadlock.
Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
---
samples/vfio-mdev/mbochs.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
index 2960e26c6ea4..6295a21381eb 100644
--- a/samples/vfio-mdev/mbochs.c
+++ b/samples/vfio-mdev/mbochs.c
@@ -178,6 +178,8 @@ static const char *vbe_name(u32 index)
return "(invalid)";
}
+static struct page *__mbochs_get_page(struct mdev_state *mdev_state,
+ pgoff_t pgoff);
static struct page *mbochs_get_page(struct mdev_state *mdev_state,
pgoff_t pgoff);
@@ -394,7 +396,7 @@ static ssize_t mdev_access(struct mdev_device *mdev, char *buf, size_t count,
MBOCHS_MEMORY_BAR_OFFSET + mdev_state->memsize) {
pos -= MBOCHS_MMIO_BAR_OFFSET;
poff = pos & ~PAGE_MASK;
- pg = mbochs_get_page(mdev_state, pos >> PAGE_SHIFT);
+ pg = __mbochs_get_page(mdev_state, pos >> PAGE_SHIFT);
map = kmap(pg);
if (is_write)
memcpy(map + poff, buf, count);
--
2.7.4
^ permalink raw reply [flat|nested] 2+ messages in thread* Re: [PATCH] sample: vfio-mdev: avoid deadlock in mdev_access()
2018-07-06 20:50 [PATCH] sample: vfio-mdev: avoid deadlock in mdev_access() Alexey Khoroshilov
@ 2018-07-11 19:30 ` Alex Williamson
0 siblings, 0 replies; 2+ messages in thread
From: Alex Williamson @ 2018-07-11 19:30 UTC (permalink / raw)
To: Alexey Khoroshilov
Cc: Gerd Hoffmann, Kirti Wankhede, kvm, linux-kernel, ldv-project
On Fri, 6 Jul 2018 23:50:06 +0300
Alexey Khoroshilov <khoroshilov@ispras.ru> wrote:
> mdev_access() calls mbochs_get_page() with mdev_state->ops_lock held,
> while mbochs_get_page() locks the mutex by itself.
> It leads to unavoidable deadlock.
>
> Found by Linux Driver Verification project (linuxtesting.org).
>
> Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
> ---
> samples/vfio-mdev/mbochs.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
> index 2960e26c6ea4..6295a21381eb 100644
> --- a/samples/vfio-mdev/mbochs.c
> +++ b/samples/vfio-mdev/mbochs.c
> @@ -178,6 +178,8 @@ static const char *vbe_name(u32 index)
> return "(invalid)";
> }
>
> +static struct page *__mbochs_get_page(struct mdev_state *mdev_state,
> + pgoff_t pgoff);
> static struct page *mbochs_get_page(struct mdev_state *mdev_state,
> pgoff_t pgoff);
>
> @@ -394,7 +396,7 @@ static ssize_t mdev_access(struct mdev_device *mdev, char *buf, size_t count,
> MBOCHS_MEMORY_BAR_OFFSET + mdev_state->memsize) {
> pos -= MBOCHS_MMIO_BAR_OFFSET;
> poff = pos & ~PAGE_MASK;
> - pg = mbochs_get_page(mdev_state, pos >> PAGE_SHIFT);
> + pg = __mbochs_get_page(mdev_state, pos >> PAGE_SHIFT);
> map = kmap(pg);
> if (is_write)
> memcpy(map + poff, buf, count);
Looks good, applied to vfio for-linus branch for v4.18. Thanks,
Alex
^ permalink raw reply [flat|nested] 2+ messages in thread
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