On Fri, Dec 21, 2018 at 11:25:41AM -0800, Linus Torvalds wrote:
> On Fri, Dec 21, 2018 at 12:32 AM kernel test robot
> wrote:
> >
> > FYI, we noticed commit df2052cc9221 ("bochs: convert to
> > drm_fb_helper_fbdev_setup/teardown") caused
> >
> > [ 487.591733] WARNING: CPU: 0 PID: 1 at
> > drivers/gpu/drm/drm_mode_config.c:478 drm_mode_config_cleanup+0x270/0x290
>
> Ok, this is apparently just a leak for what appears to be a not
> particularly interesting error case, but the warning is new to 4.20
> (*) so it would be nice to have somebody look at it.
>
> That commit is supposed to fix a leak, but there's apparently
> something still there.
> (*) the *problem* is probably not new, it's just now exposed by the
> switch to drm_mode_config_cleanup().
I concur, the issue was only revealed because a (not so interesting
error path was triggered). Reproduced this on current master
(v4.20-rc7-274-g23203e3f34c9), the trace leading up to the warning is
the same:
[ 50.008030] bochsdrmfb: enable CONFIG_FB_LITTLE_ENDIAN to support this
framebuffer
[ 50.009436] bochs-drm :00:02.0: [drm:drm_fb_helper_fbdev_setup]
*ERROR* fbdev: Failed to set configuration (ret=-38)
[ 50.011456] [drm] Initialized bochs-drm 1.0.0 20130925 for :00:02.0
on minor 2
[ 50.013604] WARNING: CPU: 1 PID: 1 at
drivers/gpu/drm/drm_mode_config.c:477 drm_mode_config_cleanup+0x280/0x2a0
[ 50.016175] CPU: 1 PID: 1 Comm: swapper/0 Tainted: GT
4.20.0-rc7 #1
[ 50.017732] EIP: drm_mode_config_cleanup+0x280/0x2a0
...
[ 50.023155] Call Trace:
[ 50.023155] ? bochs_kms_fini+0x1e/0x30
[ 50.023155] ? bochs_unload+0x18/0x40
[ 50.023155] ? bochs_pci_remove+0x18/0x30
[ 50.023155] ? pci_device_remove+0x1c/0x50
[ 50.031880] ? really_probe+0xf3/0x2d0
[ 50.031880] ? driver_probe_device+0x23/0xa0
The warning suggests that drm_framebuffer_init was called at some point without
a matching call to drm_framebuffer_cleanup. Adding dump_stack() reveals:
[ 97.673399] drm_framebuffer_init+0x17d/0x190
[ 97.674134] drm_gem_fb_alloc+0xbe/0x120
[ 97.674678] drm_gem_fbdev_fb_create+0x184/0x1c0
[ 97.675322] ? drm_gem_fb_simple_display_pipe_prepare_fb+0x20/0x20
[ 97.676771] ? drm_fb_helper_alloc_fbi+0xe1/0x120
[ 97.677408] bochsfb_create+0x245/0x5f0
[ 97.677935] ? bochsfb_mmap+0x60/0x60
[ 97.678421] __drm_fb_helper_initial_config_and_unlock+0x3d3/0x7b0
[ 97.678827] ? drm_setup_crtcs+0x1430/0x1430
[ 97.678827] drm_fb_helper_fbdev_setup+0x12b/0x230
[ 97.678827] bochs_fbdev_init+0x33/0x40
[ 97.678827] bochs_pci_probe+0x197/0x1a0
[ 97.678827] pci_device_probe+0xe9/0x180
[ 97.693848] bochsdrmfb: enable CONFIG_FB_LITTLE_ENDIAN to support this
framebuffer
[ 97.694880] bochs-drm :00:02.0: [drm:drm_fb_helper_fbdev_setup]
*ERROR* fbdev: Failed to set configuration (ret=-38)
More precisely, this is the call chain (obtained via GDB):
drm_fb_helper_fbdev_setup
-> drm_fb_helper_initial_config
-> __drm_fb_helper_initial_config_and_unlock
-> drm_fb_helper_single_fb_probe
-> bochsfb_create
-> drm_gem_fbdev_fb_create
-> drm_gem_fb_alloc
-> drm_framebuffer_init
Let's have a look at the source of the error message, keep in mind that
drm_fb_helper_fini is called on the error path:
int drm_fb_helper_fbdev_setup(struct drm_device *dev, ...) {
/* ... */
ret = drm_fb_helper_initial_config(fb_helper, preferred_bpp);
if (ret < 0) {
DRM_DEV_ERROR(dev->dev, "fbdev: Failed to set configuration
(ret=%d)\n", ret);
goto err_drm_fb_helper_fini;
}
return 0;
err_drm_fb_helper_fini:
drm_fb_helper_fini(fb_helper);
return ret;
}
The CONFIG_FB_LITTLE_ENDIAN error above suggests that this code path is reached
*after* calling bochsfb_create:
drm_fb_helper_fbdev_setup
-> drm_fb_helper_initial_config
-> __drm_fb_helper_initial_config_and_unlock
-> register_framebuffer
-> do_register_framebuffer
-> fb_check_foreignness
(prints error and propagates error code back to drm_fb_helper_fbdev_setup).
What does "drm_fb_helper_fini" do? Among other things it basically kfree's
memory associated with "fb_helper->fbdev" which was created using
"drm_fb_helper_alloc_fbi" in the "fb_probe" callback. This is sufficient for
"drm_fb_helper_generic_probe" (introduced by Noralf), but not for
"bochsfb_create" which additionally calls "drm_gem_fbdev_fb_create":
info = drm_fb_helper_alloc_fbi(helper);
if (IS_ERR(info)) {
DRM_ERROR("Failed to allocate fbi: %ld\n", PTR_ERR(info));
return PTR_ERR(info);
}
info->par = >fb.helper;
fb = drm_gem_fbdev_fb_create(bochs->dev, sizes, 0, gobj, NULL);
if (IS_ERR(fb)) {
DRM_ERROR("Failed to create framebuffer: %ld\n", PTR_ERR(fb));
return PTR_ERR(fb);
}
/*
