Re: INFO: rcu detected stall in hub_event

[Andrey Konovalov <andreyknvl@google.com>]

On Sat, Nov 23, 2019 at 1:51 AM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Thu, 21 Nov 2019, syzbot wrote:
>
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    46178223 usb: gadget: add raw-gadget interface
> > git tree:       https://github.com/google/kasan.git usb-fuzzer
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15a05836e00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=99c88c44660624e7
> > dashboard link: https://syzkaller.appspot.com/bug?extid=ec5f884c4a135aa0dbb9
> > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1061395ae00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13653d1ce00000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+ec5f884c4a135aa0dbb9@syzkaller.appspotmail.com
> >
> > rcu: INFO: rcu_sched self-detected stall on CPU
>
> > RIP: 0010:hid_apply_multiplier drivers/hid/hid-core.c:1058 [inline]
> > RIP: 0010:hid_setup_resolution_multiplier+0x33b/0x990
> > drivers/hid/hid-core.c:1114

I'm not sure, but the stack trace reminds me of this issue, so this
report might be related:

https://groups.google.com/d/msg/syzkaller-bugs/X0zVbh8aFEM/NsPcshjxBgAJ

>
> Diagnostic patch.
>
> #syz test: https://github.com/google/kasan.git 46178223
>
>  drivers/hid/hid-core.c |   17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
>
> Index: usb-devel/drivers/hid/hid-core.c
> ===================================================================
> --- usb-devel.orig/drivers/hid/hid-core.c
> +++ usb-devel/drivers/hid/hid-core.c
> @@ -1055,8 +1055,13 @@ static void hid_apply_multiplier(struct
>          */
>         multiplier_collection = &hid->collection[multiplier->usage->collection_index];
>         while (multiplier_collection->parent_idx != -1 &&
> -              multiplier_collection->type != HID_COLLECTION_LOGICAL)
> +              multiplier_collection->type != HID_COLLECTION_LOGICAL) {
> +               hid_info(hid, "collection %d %px parent %d\n",
> +       multiplier_collection - hid->collection, multiplier_collection,
> +       multiplier_collection->parent_idx);
>                 multiplier_collection = &hid->collection[multiplier_collection->parent_idx];
> +       }
> +       hid_info(hid, "Got collection\n");
>
>         effective_multiplier = hid_calculate_multiplier(hid, multiplier);
>
> @@ -1069,6 +1074,7 @@ static void hid_apply_multiplier(struct
>                                                       effective_multiplier);
>                 }
>         }
> +       hid_info(hid, "Applied multiplier\n");
>  }
>
>  /*
> @@ -1103,16 +1109,23 @@ void hid_setup_resolution_multiplier(str
>
>         rep_enum = &hid->report_enum[HID_FEATURE_REPORT];
>         list_for_each_entry(rep, &rep_enum->report_list, list) {
> +               hid_info(hid, "Start report %px maxfield %d\n",
> +       rep, rep->maxfield);
>                 for (i = 0; i < rep->maxfield; i++) {
>                         /* Ignore if report count is out of bounds. */
>                         if (rep->field[i]->report_count < 1)
>                                 continue;
>
> +                       hid_info(hid, "Field %d %px maxusage %d\n",
> +       i, rep->field[i], rep->field[i]->maxusage);
>                         for (j = 0; j < rep->field[i]->maxusage; j++) {
>                                 usage = &rep->field[i]->usage[j];
> -                               if (usage->hid == HID_GD_RESOLUTION_MULTIPLIER)
> +                               if (usage->hid == HID_GD_RESOLUTION_MULTIPLIER) {
> +                                       hid_info(hid, "Usage %d %px\n",
> +       j, usage);
>                                         hid_apply_multiplier(hid,
>                                                              rep->field[i]);
> +                               }
>                         }
>                 }
>         }
>