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Message-ID: <aNF6N8u1VIFSTaRM@linaro.org>
Date: Mon, 22 Sep 2025 18:32:55 +0200
From: Stephan Gerhold <stephan.gerhold@...aro.org>
To: Rob Clark <robin.clark@....qualcomm.com>
Cc: dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
freedreno@...ts.freedesktop.org,
Dmitry Baryshkov <lumag@...nel.org>,
Abhinav Kumar <abhinav.kumar@...ux.dev>,
Jessica Zhang <jessica.zhang@....qualcomm.com>,
Sean Paul <sean@...rly.run>,
Marijn Suijten <marijn.suijten@...ainline.org>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] drm/msm: Fix refcnt underflow in error path
Hi Rob,
On Wed, Jul 23, 2025 at 12:08:49PM -0700, Rob Clark wrote:
> If we hit an error path in GEM obj creation before msm_gem_new_handle()
> updates obj->resv to point to the gpuvm resv object, then obj->resv
> still points to &obj->_resv. In this case we don't want to decrement
> the refcount of the object being freed (since the refcnt is already
> zero). This fixes the following splat:
>
> ------------[ cut here ]------------
> refcount_t: underflow; use-after-free.
> WARNING: CPU: 9 PID: 7013 at lib/refcount.c:28 refcount_warn_saturate+0xf4/0x148
> Modules linked in: uinput snd_seq_dummy snd_hrtimer aes_ce_ccm snd_soc_wsa884x regmap_sdw q6prm_clocks q6apm_lpass_da>
> qcom_pil_info i2c_hid drm_kms_helper qcom_common qcom_q6v5 phy_snps_eusb2 qcom_geni_serial drm qcom_sysmon pinctrl_s>
> CPU: 9 UID: 1000 PID: 7013 Comm: deqp-vk Not tainted 6.16.0-rc4-debug+ #25 PREEMPT(voluntary)
> Hardware name: LENOVO 83ED/LNVNB161216, BIOS NHCN53WW 08/02/2024
> pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
> pc : refcount_warn_saturate+0xf4/0x148
> lr : refcount_warn_saturate+0xf4/0x148
> sp : ffff8000a2073920
> x29: ffff8000a2073920 x28: 0000000000000010 x27: 0000000000000010
> x26: 0000000000000042 x25: ffff000810e09800 x24: 0000000000000010
> x23: ffff8000a2073b94 x22: ffff000ddb22de00 x21: ffff000ddb22dc00
> x20: ffff000ddb22ddf8 x19: ffff0008024934e0 x18: 000000000000000a
> x17: 0000000000000000 x16: ffff9f8c67d77340 x15: 0000000000000000
> x14: 00000000ffffffff x13: 2e656572662d7265 x12: 7466612d65737520
> x11: 3b776f6c66726564 x10: 00000000ffff7fff x9 : ffff9f8c67506c70
> x8 : ffff9f8c69fa26f0 x7 : 00000000000bffe8 x6 : c0000000ffff7fff
> x5 : ffff000f53e14548 x4 : ffff6082ea2b2000 x3 : ffff0008b86ab080
> x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0008b86ab080
> Call trace:
> refcount_warn_saturate+0xf4/0x148 (P)
> msm_gem_free_object+0x248/0x260 [msm]
> drm_gem_object_free+0x24/0x40 [drm]
> msm_gem_new+0x1c4/0x1e0 [msm]
> msm_gem_new_handle+0x3c/0x1a0 [msm]
> msm_ioctl_gem_new+0x38/0x70 [msm]
> drm_ioctl_kernel+0xc8/0x138 [drm]
> drm_ioctl+0x2c8/0x618 [drm]
> __arm64_sys_ioctl+0xac/0x108
> invoke_syscall.constprop.0+0x64/0xe8
> el0_svc_common.constprop.0+0x40/0xe8
> do_el0_svc+0x24/0x38
> el0_svc+0x54/0x1d8
> el0t_64_sync_handler+0x10c/0x138
> el0t_64_sync+0x19c/0x1a0
> irq event stamp: 3698694
> hardirqs last enabled at (3698693): [<ffff9f8c675021dc>] __up_console_sem+0x74/0x90
> hardirqs last disabled at (3698694): [<ffff9f8c68ce8164>] el1_dbg+0x24/0x90
> softirqs last enabled at (3697578): [<ffff9f8c6744ec5c>] handle_softirqs+0x454/0x4b0
> softirqs last disabled at (3697567): [<ffff9f8c67360244>] __do_softirq+0x1c/0x28
> ---[ end trace 0000000000000000 ]---
>
> Fixes: b58e12a66e47 ("drm/msm: Add _NO_SHARE flag")
> Signed-off-by: Rob Clark <robin.clark@....qualcomm.com>
> ---
> drivers/gpu/drm/msm/msm_gem.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
> index 33d3354c6102..958bac4e2768 100644
> --- a/drivers/gpu/drm/msm/msm_gem.c
> +++ b/drivers/gpu/drm/msm/msm_gem.c
> @@ -1114,10 +1114,12 @@ static void msm_gem_free_object(struct drm_gem_object *obj)
> put_pages(obj);
> }
>
> - if (msm_obj->flags & MSM_BO_NO_SHARE) {
> + if (obj->resv != &obj->_resv) {
> struct drm_gem_object *r_obj =
> container_of(obj->resv, struct drm_gem_object, _resv);
>
> + WARN_ON(!(msm_obj->flags & MSM_BO_NO_SHARE));
> +
> /* Drop reference we hold to shared resv obj: */
> drm_gem_object_put(r_obj);
> }
This patch seems to break something for direct IRIS/video playback using
dmabuf. I use a simple GStreamer test pipeline for testing IRIS on X1E
(on GNOME, in case that matters):
$ gst-launch-1.0 filesrc location=bbb_sunflower_2160p_60fps_normal.mp4 \
! qtdemux name=d d.video_0 ! h264parse ! v4l2h264dec \
! capture-io-mode=dmabuf ! waylandsink
The video plays fine, but if I try to exit (CTRL+C) the display hangs
for a few seconds and then the console is spammed with pretty much
exactly the messages that you tried to fix here. If I revert this patch,
everything is fine again. It feels like your patch does exactly the
opposite for this use case. :-)
It seems to run into the WARN_ON you added.
Any ideas?
linux-next should have IRIS support for the Slim 7x if you want to try
this for yourself. Or alternatively, there is a backport for 6.17-rc7 in
the Linaro arm64-laptops tree: https://gitlab.com/Linaro/arm64-laptops/linux
You can find the test video here:
https://download.blender.org/demo/movies/BBB/
Thanks,
Stephan
[ 107.430721] ------------[ cut here ]------------
[ 107.435513] WARNING: CPU: 3 PID: 2040 at drivers/gpu/drm/msm/msm_gem.c:1127 msm_gem_free_object+0x1f8/0x264 [msm]
[ 107.630472] CPU: 3 UID: 1000 PID: 2040 Comm: .gnome-shell-wr Not tainted 6.17.0-rc7 #1 PREEMPT
[ 107.630482] pstate: 81400005 (Nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[ 107.630488] pc : msm_gem_free_object+0x1f8/0x264 [msm]
[ 107.676630] lr : msm_gem_free_object+0x138/0x264 [msm]
[ 107.676666] sp : ffff800092a1bb30
[ 107.676668] x29: ffff800092a1bb80 x28: ffff800092a1bce8 x27: ffffbc702dbdbe08
[ 107.676676] x26: 0000000000000008 x25: 0000000000000009 x24: 00000000000000a6
[ 107.676682] x23: ffff00083c72f850 x22: ffff00083c72f868 x21: ffff00087e69f200
[ 107.676689] x20: ffff00087e69f330 x19: ffff00084d157ae0 x18: 0000000000000000
[ 107.676695] x17: 0000000000000000 x16: ffffbc704bd46b80 x15: 0000ffffd0959540
[ 107.676701] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
[ 107.676706] x11: ffffbc702e6cdb48 x10: 0000000000000000 x9 : 000000000000003f
[ 107.676712] x8 : ffff800092a1ba90 x7 : 0000000000000000 x6 : 0000000000000020
[ 107.676718] x5 : ffffbc704bd46c40 x4 : fffffdffe102cf60 x3 : 0000000000400032
[ 107.676724] x2 : 0000000000020000 x1 : ffff00087e6978e8 x0 : ffff00087e6977e8
[ 107.676731] Call trace:
[ 107.676733] msm_gem_free_object+0x1f8/0x264 [msm] (P)
[ 107.676771] drm_gem_object_free+0x1c/0x30 [drm]
[ 107.676816] drm_gem_object_handle_put_unlocked+0x138/0x150 [drm]
[ 107.676852] drm_gem_object_release_handle+0x5c/0xcc [drm]
[ 107.676886] drm_gem_handle_delete+0x68/0xbc [drm]
[ 107.788743] drm_gem_close_ioctl+0x34/0x40 [drm]
[ 107.793553] drm_ioctl_kernel+0xc0/0x130 [drm]
[ 107.798178] drm_ioctl+0x360/0x4e0 [drm]
[ 107.802277] __arm64_sys_ioctl+0xac/0x104
[ 107.806436] invoke_syscall+0x48/0x104
[ 107.810334] el0_svc_common.constprop.0+0x40/0xe0
[ 107.815209] do_el0_svc+0x1c/0x28
[ 107.818662] el0_svc+0x34/0xec
[ 107.821838] el0t_64_sync_handler+0xa0/0xe4
[ 107.826173] el0t_64_sync+0x198/0x19c
[ 107.829971] ---[ end trace 0000000000000000 ]---
[ 107.834789] ------------[ cut here ]------------
[ 107.839587] refcount_t: underflow; use-after-free.
[ 107.844553] WARNING: CPU: 3 PID: 2040 at lib/refcount.c:28 refcount_warn_saturate+0xf4/0x144
[ 108.052928] CPU: 3 UID: 1000 PID: 2040 Comm: .gnome-shell-wr Tainted: G W 6.17.0-rc7 #1 PREEMPT
[ 108.063491] Tainted: [W]=WARN
[ 108.075627] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[ 108.082808] pc : refcount_warn_saturate+0xf4/0x144
[ 108.087756] lr : refcount_warn_saturate+0xf4/0x144
[ 108.092704] sp : ffff800092a1bb20
[ 108.096141] x29: ffff800092a1bb20 x28: ffff800092a1bce8 x27: ffffbc702dbdbe08
[ 108.103491] x26: 0000000000000008 x25: 0000000000000009 x24: 00000000000000a6
[ 108.110852] x23: ffff00083c72f850 x22: ffff00083c72f868 x21: ffff00087e69f200
[ 108.118222] x20: ffff00087e69f330 x19: ffff00084d157ae0 x18: 0000000000000006
[ 108.125572] x17: 0000000000000000 x16: ffffbc704ba1eda0 x15: ffff800092a1b6ef
[ 108.132925] x14: 000000000000003a x13: 000000000000003a x12: 0000000000000000
[ 108.140280] x11: 00000000000000c0 x10: d2c95932de8ceaa3 x9 : 128386994077d608
[ 108.147631] x8 : ffff000840c0c588 x7 : 0000000002ac3ea0 x6 : 0000000000000002
[ 108.154990] x5 : 0000000435572e2f x4 : 0000000000000002 x3 : 0000000000000010
[ 108.162339] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff000840c0b480
[ 108.169697] Call trace:
[ 108.172243] refcount_warn_saturate+0xf4/0x144 (P)
[ 108.177199] msm_gem_free_object+0x25c/0x264 [msm]
[ 108.182167] drm_gem_object_free+0x1c/0x30 [drm]
[ 108.186943] drm_gem_object_handle_put_unlocked+0x138/0x150 [drm]
[ 108.193237] drm_gem_object_release_handle+0x5c/0xcc [drm]
[ 108.198906] drm_gem_handle_delete+0x68/0xbc [drm]
[ 108.203867] drm_gem_close_ioctl+0x34/0x40 [drm]
[ 108.208651] drm_ioctl_kernel+0xc0/0x130 [drm]
[ 108.213248] drm_ioctl+0x360/0x4e0 [drm]
[ 108.217319] __arm64_sys_ioctl+0xac/0x104
[ 108.221464] invoke_syscall+0x48/0x104
[ 108.225343] el0_svc_common.constprop.0+0x40/0xe0
[ 108.230207] do_el0_svc+0x1c/0x28
[ 108.233650] el0_svc+0x34/0xec
[ 108.236817] el0t_64_sync_handler+0xa0/0xe4
[ 108.241143] el0t_64_sync+0x198/0x19c
[ 108.244931] ---[ end trace 0000000000000000 ]---
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