On Tue, Apr 13, 2021 at 4:08 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
>
> On 13/04/2021 04:43, Alexandre Courbot wrote:
> > Hi Hans,
> >
> > On Mon, Apr 12, 2021 at 8:51 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
> >>
> >> When controls are used together with the Request API, then for
> >> each request a v4l2_ctrl_handler struct is allocated. This contains
> >> the controls that can be set in a request. If a control is *not* set in
> >> the request, then the value used in the most recent previous request
> >> must be used, or the current value if it is not found in any outstanding
> >> requests.
> >>
> >> The framework tried to find such a previous request and it would set
> >> the 'req' pointer in struct v4l2_ctrl_ref to the v4l2_ctrl_ref of the
> >> control in such a previous request. So far, so good. However, when that
> >> previous request was applied to the hardware, returned to userspace, and
> >> then userspace would re-init or free that request, any 'ref' pointer in
> >> still-queued requests would suddenly point to freed memory.
> >>
> >> This was not noticed before since the drivers that use this expected
> >> that each request would always have the controls set, so there was
> >> never any need to find a control in older requests. This requirement
> >> was relaxed, and now this bug surfaced.
> >>
> >> The use of the 'req' pointer in v4l2_ctrl_ref was very fragile, so
> >> drop this entirely. Instead add a valid_p_req bool to indicate that
> >> p_req contains a valid value for this control. And if it is false,
> >> then just use the current value of the control.
> >>
> >> Note that VIDIOC_G_EXT_CTRLS will always return -EACCES when attempting
> >> to get a control from a request until the request is completed. And in
> >> that case, all controls in the request will have the control value set
> >> (i.e. valid_p_req is true). This means that the whole 'find the most
> >> recent previous request containing a control' idea is pointless, and
> >> the code can be simplified considerably.
> >>
> >> The v4l2_g_ext_ctrls_common() function was refactored a bit to make
> >> it more understandable. It also avoids updating volatile controls
> >> in a completed request since that was already done when the request
> >> was completed.
> >>
> >> Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
> >> Fixes: 6fa6f831f095 ("media: v4l2-ctrls: add core request support")
> >> Cc: <stable@xxxxxxxxxxxxxxx> # for v5.9 and up
> >
> > Tested-by: Alexandre Courbot <acourbot@xxxxxxxxxxxx>
> >
> > Thanks for this! I cannot reproduce the crash anymore on mtk-vcodec
> > after hundreds of attempts.
> >
> > Interestingly we are also running the same driver on a 4.19 kernel
> > with requests support and H.264 stateless backported (up to and
> > including "media: v4l2-ctrl: Lock main_hdl on operations of
> > requests_queued") and we are not seeing this issue on that tree. So
>
> Just for fun, try backporting 2fae4d6aabc8 ("media: v4l2-ctrls:
> v4l2_ctrl_request_complete() should always set ref->req") and see if that
> triggers the same bug in 4.19. I suspect that that patch makes the problem
> more likely to happen.
I tried doing the opposite (reverting 2fae4d6aabc8 ("media: v4l2-ctrls:
> v4l2_ctrl_request_complete() should always set ref->req") on our tree that crashed) and indeed I cannot reproduce the issue either! That's fascinating. Shouldn't change the fact that we ought to take all the patches in both trees though...
Thanks again for the fix, it really helps us!
>
> Regards,
>
> Hans
>
> > despite all evidence pointing to the initial request support there may
> > also be other conditions where this issue does not manifest itself.
> > Anyway for safety I will make sure to port this and the missing
> > requests patches into that tree as well.
> >
> > Cheers,
> > Alex.
> >
> >> ---
> >> While the bug was actually introduced when the Request API was merged,
> >> it was not in active use until the H.264 stateless codec API was made
> >> part of the uAPI. That's why the CC to stable explicitly says v5.9 and
> >> up, since this patch won't apply for older kernels, and that's OK since
> >> it was not in active use AFAIK.
> >>
> >> If that assumption is wrong, then let me know and I will have to create
> >> custom patches for older kernels, but I prefer to avoid doing that.
> >>
> >> I'm not planning to get this merged for 5.12 since we are close to a
> >> release, so I think it is OK to get this in for 5.13 and have it backported
> >> to 5.12. I also would like to have feedback from Alexandre and Yunfei
> >> that this patch indeed fixes your issues as well.
> >>
> >> I plan on creating better tests in v4l2-compliance using vivid to verify
> >> correct behavior of controls in requests. Proper tests are definitely
> >> needed to avoid bugs like this.
> >>
> >> Changes since v1:
> >> - drop find_ctrl_in_prev_request() as it is actually not needed
> >> - refactor v4l2_g_ext_ctrls_common() a little bit to make it easier
> >> to understand
> >>
> >> Regards,
> >>
> >> Hans
> >> ---
> >> drivers/media/v4l2-core/v4l2-ctrls.c | 137 ++++++++++++---------------
> >> include/media/v4l2-ctrls.h | 12 ++-
> >> 2 files changed, 70 insertions(+), 79 deletions(-)
> >>
> >> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> >> index c7bcc5c25771..0d7fe1bd975a 100644
> >> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> >> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> >> @@ -2504,7 +2504,16 @@ static void new_to_req(struct v4l2_ctrl_ref *ref)
> >> if (!ref)
> >> return;
> >> ptr_to_ptr(ref->ctrl, ref->ctrl->p_new, ref->p_req);
> >> - ref->req = ref;
> >> + ref->valid_p_req = true;
> >> +}
> >> +
> >> +/* Copy the current value to the request value */
> >> +static void cur_to_req(struct v4l2_ctrl_ref *ref)
> >> +{
> >> + if (!ref)
> >> + return;
> >> + ptr_to_ptr(ref->ctrl, ref->ctrl->p_cur, ref->p_req);
> >> + ref->valid_p_req = true;
> >> }
> >>
> >> /* Copy the request value to the new value */
> >> @@ -2512,8 +2521,8 @@ static void req_to_new(struct v4l2_ctrl_ref *ref)
> >> {
> >> if (!ref)
> >> return;
> >> - if (ref->req)
> >> - ptr_to_ptr(ref->ctrl, ref->req->p_req, ref->ctrl->p_new);
> >> + if (ref->valid_p_req)
> >> + ptr_to_ptr(ref->ctrl, ref->p_req, ref->ctrl->p_new);
> >> else
> >> ptr_to_ptr(ref->ctrl, ref->ctrl->p_cur, ref->ctrl->p_new);
> >> }
> >> @@ -3694,39 +3703,8 @@ static void v4l2_ctrl_request_queue(struct media_request_object *obj)
> >> struct v4l2_ctrl_handler *hdl =
> >> container_of(obj, struct v4l2_ctrl_handler, req_obj);
> >> struct v4l2_ctrl_handler *main_hdl = obj->priv;
> >> - struct v4l2_ctrl_handler *prev_hdl = NULL;
> >> - struct v4l2_ctrl_ref *ref_ctrl, *ref_ctrl_prev = NULL;
> >>
> >> mutex_lock(main_hdl->lock);
> >> - if (list_empty(&main_hdl->requests_queued))
> >> - goto queue;
> >> -
> >> - prev_hdl = list_last_entry(&main_hdl->requests_queued,
> >> - struct v4l2_ctrl_handler, requests_queued);
> >> - /*
> >> - * Note: prev_hdl and hdl must contain the same list of control
> >> - * references, so if any differences are detected then that is a
> >> - * driver bug and the WARN_ON is triggered.
> >> - */
> >> - mutex_lock(prev_hdl->lock);
> >> - ref_ctrl_prev = list_first_entry(&prev_hdl->ctrl_refs,
> >> - struct v4l2_ctrl_ref, node);
> >> - list_for_each_entry(ref_ctrl, &hdl->ctrl_refs, node) {
> >> - if (ref_ctrl->req)
> >> - continue;
> >> - while (ref_ctrl_prev->ctrl->id < ref_ctrl->ctrl->id) {
> >> - /* Should never happen, but just in case... */
> >> - if (list_is_last(&ref_ctrl_prev->node,
> >> - &prev_hdl->ctrl_refs))
> >> - break;
> >> - ref_ctrl_prev = list_next_entry(ref_ctrl_prev, node);
> >> - }
> >> - if (WARN_ON(ref_ctrl_prev->ctrl->id != ref_ctrl->ctrl->id))
> >> - break;
> >> - ref_ctrl->req = ref_ctrl_prev->req;
> >> - }
> >> - mutex_unlock(prev_hdl->lock);
> >> -queue:
> >> list_add_tail(&hdl->requests_queued, &main_hdl->requests_queued);
> >> hdl->request_is_queued = true;
> >> mutex_unlock(main_hdl->lock);
> >> @@ -3783,7 +3761,7 @@ v4l2_ctrl_request_hdl_ctrl_find(struct v4l2_ctrl_handler *hdl, u32 id)
> >> {
> >> struct v4l2_ctrl_ref *ref = find_ref_lock(hdl, id);
> >>
> >> - return (ref && ref->req == ref) ? ref->ctrl : NULL;
> >> + return (ref && ref->valid_p_req) ? ref->ctrl : NULL;
> >> }
> >> EXPORT_SYMBOL_GPL(v4l2_ctrl_request_hdl_ctrl_find);
> >>
> >> @@ -3972,7 +3950,13 @@ static int class_check(struct v4l2_ctrl_handler *hdl, u32 which)
> >> return find_ref_lock(hdl, which | 1) ? 0 : -EINVAL;
> >> }
> >>
> >> -/* Get extended controls. Allocates the helpers array if needed. */
> >> +/*
> >> + * Get extended controls. Allocates the helpers array if needed.
> >> + *
> >> + * Note that v4l2_g_ext_ctrls_common() with 'which' set to
> >> + * V4L2_CTRL_WHICH_REQUEST_VAL is only called if the request was
> >> + * completed, and in that case valid_p_req is true for all controls.
> >> + */
> >> static int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
> >> struct v4l2_ext_controls *cs,
> >> struct video_device *vdev)
> >> @@ -3981,9 +3965,10 @@ static int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
> >> struct v4l2_ctrl_helper *helpers = helper;
> >> int ret;
> >> int i, j;
> >> - bool def_value;
> >> + bool is_default, is_request;
> >>
> >> - def_value = (cs->which == V4L2_CTRL_WHICH_DEF_VAL);
> >> + is_default = (cs->which == V4L2_CTRL_WHICH_DEF_VAL);
> >> + is_request = (cs->which == V4L2_CTRL_WHICH_REQUEST_VAL);
> >>
> >> cs->error_idx = cs->count;
> >> cs->which = V4L2_CTRL_ID2WHICH(cs->which);
> >> @@ -4009,11 +3994,9 @@ static int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
> >> ret = -EACCES;
> >>
> >> for (i = 0; !ret && i < cs->count; i++) {
> >> - int (*ctrl_to_user)(struct v4l2_ext_control *c,
> >> - struct v4l2_ctrl *ctrl);
> >> struct v4l2_ctrl *master;
> >> -
> >> - ctrl_to_user = def_value ? def_to_user : cur_to_user;
> >> + bool is_volatile = false;
> >> + u32 idx = i;
> >>
> >> if (helpers[i].mref == NULL)
> >> continue;
> >> @@ -4023,31 +4006,48 @@ static int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
> >>
> >> v4l2_ctrl_lock(master);
> >>
> >> - /* g_volatile_ctrl will update the new control values */
> >> - if (!def_value &&
> >> + /*
> >> + * g_volatile_ctrl will update the new control values.
> >> + * This makes no sense for V4L2_CTRL_WHICH_DEF_VAL and
> >> + * V4L2_CTRL_WHICH_REQUEST_VAL. In the case of requests
> >> + * it is v4l2_ctrl_request_complete() that copies the
> >> + * volatile controls at the time of request completion
> >> + * to the request, so you don't want to do that again.
> >> + */
> >> + if (!is_default && !is_request &&
> >> ((master->flags & V4L2_CTRL_FLAG_VOLATILE) ||
> >> (master->has_volatiles && !is_cur_manual(master)))) {
> >> for (j = 0; j < master->ncontrols; j++)
> >> cur_to_new(master->cluster[j]);
> >> ret = call_op(master, g_volatile_ctrl);
> >> - ctrl_to_user = new_to_user;
> >> + is_volatile = true;
> >> }
> >> - /* If OK, then copy the current (for non-volatile controls)
> >> - or the new (for volatile controls) control values to the
> >> - caller */
> >> - if (!ret) {
> >> - u32 idx = i;
> >>
> >> - do {
> >> - if (helpers[idx].ref->req)
> >> - ret = req_to_user(cs->controls + idx,
> >> - helpers[idx].ref->req);
> >> - else
> >> - ret = ctrl_to_user(cs->controls + idx,
> >> - helpers[idx].ref->ctrl);
> >> - idx = helpers[idx].next;
> >> - } while (!ret && idx);
> >> + if (ret) {
> >> + v4l2_ctrl_unlock(master);
> >> + break;
> >> }
> >> +
> >> + /*
> >> + * Copy the default value (if is_default is true), the
> >> + * request value (if is_request is true and p_req is valid),
> >> + * the new volatile value (if is_volatile is true) or the
> >> + * current value.
> >> + */
> >> + do {
> >> + struct v4l2_ctrl_ref *ref = helpers[idx].ref;
> >> +
> >> + if (is_default)
> >> + ret = def_to_user(cs->controls + idx, ref->ctrl);
> >> + else if (is_request && ref->valid_p_req)
> >> + ret = req_to_user(cs->controls + idx, ref);
> >> + else if (is_volatile)
> >> + ret = new_to_user(cs->controls + idx, ref->ctrl);
> >> + else
> >> + ret = cur_to_user(cs->controls + idx, ref->ctrl);
> >> + idx = helpers[idx].next;
> >> + } while (!ret && idx);
> >> +
> >> v4l2_ctrl_unlock(master);
> >> }
> >>
> >> @@ -4690,8 +4690,6 @@ void v4l2_ctrl_request_complete(struct media_request *req,
> >> unsigned int i;
> >>
> >> if (ctrl->flags & V4L2_CTRL_FLAG_VOLATILE) {
> >> - ref->req = ref;
> >> -
> >> v4l2_ctrl_lock(master);
> >> /* g_volatile_ctrl will update the current control values */
> >> for (i = 0; i < master->ncontrols; i++)
> >> @@ -4701,21 +4699,12 @@ void v4l2_ctrl_request_complete(struct media_request *req,
> >> v4l2_ctrl_unlock(master);
> >> continue;
> >> }
> >> - if (ref->req == ref)
> >> + if (ref->valid_p_req)
> >> continue;
> >>
> >> + /* Copy the current control value into the request */
> >> v4l2_ctrl_lock(ctrl);
> >> - if (ref->req) {
> >> - ptr_to_ptr(ctrl, ref->req->p_req, ref->p_req);
> >> - } else {
> >> - ptr_to_ptr(ctrl, ctrl->p_cur, ref->p_req);
> >> - /*
> >> - * Set ref->req to ensure that when userspace wants to
> >> - * obtain the controls of this request it will take
> >> - * this value and not the current value of the control.
> >> - */
> >> - ref->req = ref;
> >> - }
> >> + cur_to_req(ref);
> >> v4l2_ctrl_unlock(ctrl);
> >> }
> >>
> >> @@ -4779,7 +4768,7 @@ int v4l2_ctrl_request_setup(struct media_request *req,
> >> struct v4l2_ctrl_ref *r =
> >> find_ref(hdl, master->cluster[i]->id);
> >>
> >> - if (r->req && r == r->req) {
> >> + if (r->valid_p_req) {
> >> have_new_data = true;
> >> break;
> >> }
> >> diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
> >> index c1d20bd8f25f..a5953b812878 100644
> >> --- a/include/media/v4l2-ctrls.h
> >> +++ b/include/media/v4l2-ctrls.h
> >> @@ -304,12 +304,14 @@ struct v4l2_ctrl {
> >> * the control has been applied. This prevents applying controls
> >> * from a cluster with multiple controls twice (when the first
> >> * control of a cluster is applied, they all are).
> >> - * @req: If set, this refers to another request that sets this control.
> >> + * @valid_p_req: If set, then p_req contains the control value for the request.
> >> * @p_req: If the control handler containing this control reference
> >> * is bound to a media request, then this points to the
> >> - * value of the control that should be applied when the request
> >> + * value of the control that must be applied when the request
> >> * is executed, or to the value of the control at the time
> >> - * that the request was completed.
> >> + * that the request was completed. If @valid_p_req is false,
> >> + * then this control was never set for this request and the
> >> + * control will not be updated when this request is applied.
> >> *
> >> * Each control handler has a list of these refs. The list_head is used to
> >> * keep a sorted-by-control-ID list of all controls, while the next pointer
> >> @@ -322,7 +324,7 @@ struct v4l2_ctrl_ref {
> >> struct v4l2_ctrl_helper *helper;
> >> bool from_other_dev;
> >> bool req_done;
> >> - struct v4l2_ctrl_ref *req;
> >> + bool valid_p_req;
> >> union v4l2_ctrl_ptr p_req;
> >> };
> >>
> >> @@ -349,7 +351,7 @@ struct v4l2_ctrl_ref {
> >> * @error: The error code of the first failed control addition.
> >> * @request_is_queued: True if the request was queued.
> >> * @requests: List to keep track of open control handler request objects.
> >> - * For the parent control handler (@req_obj.req == NULL) this
> >> + * For the parent control handler (@req_obj.ops == NULL) this
> >> * is the list header. When the parent control handler is
> >> * removed, it has to unbind and put all these requests since
> >> * they refer to the parent.
> >> --
> >> 2.30.2
> >>
>
