The error paths of gntdev_mmap() can call unmap_grant_pages() even
though not all of the pages have been successfully mapped. This will
trigger the WARN_ON()s in __unmap_grant_pages_done(). The number of
warnings can be very large; I have observed thousands of lines of
warnings in the systemd journal.
Avoid this problem by only warning on unmapping failure if the handle
being unmapped is not INVALID_GRANT_HANDLE. The handle field of any
page that was not successfully mapped will be INVALID_GRANT_HANDLE, so
this catches all cases where unmapping can legitimately fail.
Suggested-by: Juergen Gross <[email protected]>
Cc: [email protected]
Signed-off-by: Demi Marie Obenour <[email protected]>
Fixes: dbe97cff7dd9 ("xen/gntdev: Avoid blocking in unmap_grant_pages()")
---
drivers/xen/gntdev.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
Changes since v2:
- Use unmap_ops instead of kunmap_ops in the first WARN_ON
Changes since v1:
- Explicitly check for a status other than GNTST_okay instead of
implicitly checking that it is nonzero.
- Avoid wrapping a line as within a comparison, as this makes the code
hard to read.
diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 4b56c39f766d4da68570d08d963f6ef40c8d9c37..84b143eef395b1585f3a8c0fdcb301ce9fbc52ec 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -396,13 +396,15 @@ static void __unmap_grant_pages_done(int result,
unsigned int offset = data->unmap_ops - map->unmap_ops;
for (i = 0; i < data->count; i++) {
- WARN_ON(map->unmap_ops[offset+i].status);
+ WARN_ON(map->unmap_ops[offset + i].status != GNTST_okay &&
+ map->unmap_ops[offset + i].handle != INVALID_GRANT_HANDLE);
pr_debug("unmap handle=%d st=%d\n",
map->unmap_ops[offset+i].handle,
map->unmap_ops[offset+i].status);
map->unmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
if (use_ptemod) {
- WARN_ON(map->kunmap_ops[offset+i].status);
+ WARN_ON(map->kunmap_ops[offset + i].status != GNTST_okay &&
+ map->kunmap_ops[offset + i].handle != INVALID_GRANT_HANDLE);
pr_debug("kunmap handle=%u st=%d\n",
map->kunmap_ops[offset+i].handle,
map->kunmap_ops[offset+i].status);
--
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab
On 11.07.22 02:05, Demi Marie Obenour wrote:
Hello Demi Marie
> The error paths of gntdev_mmap() can call unmap_grant_pages() even
> though not all of the pages have been successfully mapped. This will
> trigger the WARN_ON()s in __unmap_grant_pages_done(). The number of
> warnings can be very large; I have observed thousands of lines of
> warnings in the systemd journal.
>
> Avoid this problem by only warning on unmapping failure if the handle
> being unmapped is not INVALID_GRANT_HANDLE. The handle field of any
> page that was not successfully mapped will be INVALID_GRANT_HANDLE, so
> this catches all cases where unmapping can legitimately fail.
>
> Suggested-by: Juergen Gross <[email protected]>
> Cc: [email protected]
> Signed-off-by: Demi Marie Obenour <[email protected]>
> Fixes: dbe97cff7dd9 ("xen/gntdev: Avoid blocking in unmap_grant_pages()")
Reviewed-by: Oleksandr Tyshchenko <[email protected]>
> ---
> drivers/xen/gntdev.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> Changes since v2:
>
> - Use unmap_ops instead of kunmap_ops in the first WARN_ON
>
> Changes since v1:
>
> - Explicitly check for a status other than GNTST_okay instead of
> implicitly checking that it is nonzero.
> - Avoid wrapping a line as within a comparison, as this makes the code
> hard to read.
>
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index 4b56c39f766d4da68570d08d963f6ef40c8d9c37..84b143eef395b1585f3a8c0fdcb301ce9fbc52ec 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -396,13 +396,15 @@ static void __unmap_grant_pages_done(int result,
> unsigned int offset = data->unmap_ops - map->unmap_ops;
>
> for (i = 0; i < data->count; i++) {
> - WARN_ON(map->unmap_ops[offset+i].status);
> + WARN_ON(map->unmap_ops[offset + i].status != GNTST_okay &&
> + map->unmap_ops[offset + i].handle != INVALID_GRANT_HANDLE);
> pr_debug("unmap handle=%d st=%d\n",
> map->unmap_ops[offset+i].handle,
> map->unmap_ops[offset+i].status);
> map->unmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
> if (use_ptemod) {
> - WARN_ON(map->kunmap_ops[offset+i].status);
> + WARN_ON(map->kunmap_ops[offset + i].status != GNTST_okay &&
> + map->kunmap_ops[offset + i].handle != INVALID_GRANT_HANDLE);
> pr_debug("kunmap handle=%u st=%d\n",
> map->kunmap_ops[offset+i].handle,
> map->kunmap_ops[offset+i].status);
--
Regards,
Oleksandr Tyshchenko
On 11.07.22 01:05, Demi Marie Obenour wrote:
> The error paths of gntdev_mmap() can call unmap_grant_pages() even
> though not all of the pages have been successfully mapped. This will
> trigger the WARN_ON()s in __unmap_grant_pages_done(). The number of
> warnings can be very large; I have observed thousands of lines of
> warnings in the systemd journal.
>
> Avoid this problem by only warning on unmapping failure if the handle
> being unmapped is not INVALID_GRANT_HANDLE. The handle field of any
> page that was not successfully mapped will be INVALID_GRANT_HANDLE, so
> this catches all cases where unmapping can legitimately fail.
>
> Suggested-by: Juergen Gross <[email protected]>
> Cc: [email protected]
> Signed-off-by: Demi Marie Obenour <[email protected]>
> Fixes: dbe97cff7dd9 ("xen/gntdev: Avoid blocking in unmap_grant_pages()")
Reviewed-by: Juergen Gross <[email protected]>
Juergen
On 11.07.22 01:05, Demi Marie Obenour wrote:
> The error paths of gntdev_mmap() can call unmap_grant_pages() even
> though not all of the pages have been successfully mapped. This will
> trigger the WARN_ON()s in __unmap_grant_pages_done(). The number of
> warnings can be very large; I have observed thousands of lines of
> warnings in the systemd journal.
>
> Avoid this problem by only warning on unmapping failure if the handle
> being unmapped is not INVALID_GRANT_HANDLE. The handle field of any
> page that was not successfully mapped will be INVALID_GRANT_HANDLE, so
> this catches all cases where unmapping can legitimately fail.
>
> Suggested-by: Juergen Gross <[email protected]>
> Cc: [email protected]
> Signed-off-by: Demi Marie Obenour <[email protected]>
> Fixes: dbe97cff7dd9 ("xen/gntdev: Avoid blocking in unmap_grant_pages()")
Pushed to xen/tip.git for-linus-5.19a
Juergen