Quoting Christian König (2020-05-20 13:19:42)
> Am 20.05.20 um 14:14 schrieb Nirmoy Das:
> > drm_gem_fb_destroy() calls drm_gem_object_put() with NULL obj causing:
> > [ 11.584209] BUG: kernel NULL pointer dereference, address: 0000000000000000
> > [ 11.584213] #PF: supervisor write access in kernel mode
> > [ 11.584215] #PF: error_code(0x0002) - not-present page
> > [ 11.584216] PGD 0 P4D 0
> > [ 11.584220] Oops: 0002 [#1] SMP NOPTI
> > [ 11.584223] CPU: 7 PID: 1571 Comm: gnome-shell Tainted: G E 5.7.0-rc1-1-default+ #27
> > [ 11.584225] Hardware name: Micro-Star International Co., Ltd. MS-7A31/X370 XPOWER GAMING TITANIUM (MS-7A31), BIOS 1.MR 12/03/2019
> > [ 11.584237] RIP: 0010:drm_gem_fb_destroy+0x28/0x70 [drm_kms_helper]
> > <snip>
> > [ 11.584256] Call Trace:
> > [ 11.584279] drm_mode_rmfb+0x189/0x1c0 [drm]
> > [ 11.584299] ? drm_mode_rmfb+0x1c0/0x1c0 [drm]
> > [ 11.584314] drm_ioctl_kernel+0xaa/0xf0 [drm]
> > [ 11.584329] drm_ioctl+0x1ff/0x3b0 [drm]
> > [ 11.584347] ? drm_mode_rmfb+0x1c0/0x1c0 [drm]
> > [ 11.584421] amdgpu_drm_ioctl+0x49/0x80 [amdgpu]
> > [ 11.584427] ksys_ioctl+0x87/0xc0
> > [ 11.584430] __x64_sys_ioctl+0x16/0x20
> > [ 11.584434] do_syscall_64+0x5f/0x240
> > [ 11.584438] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > [ 11.584440] RIP: 0033:0x7f0ef80f7227
> >
> > Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxx>
>
> Fixes: .... missing here. Apart from that Reviewed-by: Christian König
> <christian.koenig@xxxxxxx>.
>
> Please resend with the tag added, then I'm going to push this to
> drm-misc-next asap.
>
> Christian.
>
> > ---
> > include/drm/drm_gem.h | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> > index 52173abdf500..a13510346a9b 100644
> > --- a/include/drm/drm_gem.h
> > +++ b/include/drm/drm_gem.h
> > @@ -372,6 +372,9 @@ static inline void drm_gem_object_get(struct drm_gem_object *obj)
> > static inline void
> > drm_gem_object_put(struct drm_gem_object *obj)
> > {
> > + if (!obj)
> > + return;
> > +
This adds several thousand NULL checks where there were previously none.
I doubt the compiler eliminates them all.
I'd suggest reverting
b5d250744ccc ("drm/gem: fold drm_gem_object_put_unlocked and __drm_gem_object_put()")
-Chris
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