Re: WARNING in drm_modeset_lock_all

[Daniel Vetter]

On Mon, Oct 30, 2017 at 02:24:32PM +0000, Chris Wilson wrote:
> Quoting syzbot (2017-10-27 09:09:50)
> > Hello,
> > 
> > syzkaller hit the following crash on  
> > 6f20b7a58cb9c0fe00badcdfd65b1f4a8f28dfc6
> > git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> > compiler: gcc (GCC) 7.1.1 20170620
> > .config is attached
> > Raw console output is attached.
> > 
> > 
> > 
> > 
> > ------------[ cut here ]------------
> > WARNING: CPU: 2 PID: 11675 at drivers/gpu/drm/drm_modeset_lock.c:92  
> > drm_modeset_lock_all+0x1fc/0x2d0 drivers/gpu/drm/drm_modeset_lock.c:92
> > Kernel panic - not syncing: panic_on_warn set ...
> > 
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> > Call Trace:
> >   __dump_stack lib/dump_stack.c:16 [inline]
> >   dump_stack+0x194/0x257 lib/dump_stack.c:52
> >   fail_dump lib/fault-inject.c:51 [inline]
> >   should_fail+0x8c0/0xa40 lib/fault-inject.c:149
> >   should_failslab+0xec/0x120 mm/failslab.c:31
> >   slab_pre_alloc_hook mm/slab.h:422 [inline]
> >   slab_alloc mm/slab.c:3383 [inline]
> >   kmem_cache_alloc_trace+0x4b/0x750 mm/slab.c:3625
> >   kmalloc include/linux/slab.h:493 [inline]
> >   kzalloc include/linux/slab.h:666 [inline]
> >   drm_modeset_lock_all+0x49/0x2d0 drivers/gpu/drm/drm_modeset_lock.c:91
> >   drm_mode_obj_get_properties_ioctl+0x87/0x2b0  
> > drivers/gpu/drm/drm_mode_object.c:359
> >   drm_ioctl_kernel+0x1e7/0x2e0 drivers/gpu/drm/drm_ioctl.c:735
> >   drm_ioctl+0x72e/0xa50 drivers/gpu/drm/drm_ioctl.c:831
> >   vfs_ioctl fs/ioctl.c:45 [inline]
> >   do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:685
> >   SYSC_ioctl fs/ioctl.c:700 [inline]
> >   SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
> >   entry_SYSCALL_64_fastpath+0x1f/0xbe
> 
> This bug is for the unexpected allocation failure inside
> drm_modeset_lock_all() (in this case from should_fail). To properly
> document this behaviour, we should probably use
> 
> diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
> index e123497da0ca..963e23db0fe7 100644
> --- a/drivers/gpu/drm/drm_modeset_lock.c
> +++ b/drivers/gpu/drm/drm_modeset_lock.c
> @@ -93,7 +93,7 @@ void drm_modeset_lock_all(struct drm_device *dev)
>         struct drm_modeset_acquire_ctx *ctx;
>         int ret;
>  
> -       ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
> +       ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
>         if (WARN_ON(!ctx))
>                 return;
> 
> Then it will turn up on somebody'ss too-small-to-fail fix list.

lgtm. Can you pls submit this as a patch withs sob and everything?

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch