Am 20.05.20 um 14:49 schrieb Chris Wilson:
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()")
I didn't looked into this patch in detail, but allowing to call *_put()
functions with NULL and nothing bad happens is rather common practice.
On the other hand I agree that this might cause a performance problem.
How many sites do we have which could call drm_gem_object_put() with NULL?
Christian.
-Chris
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