linux-kernel - [PATCH] drm/msm: Fix GEM free for imported dma-bufs

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Message-ID: <20250923140441.746081-1-robin.clark@oss.qualcomm.com>
Date: Tue, 23 Sep 2025 07:04:40 -0700
From: Rob Clark <robin.clark@....qualcomm.com>
To: dri-devel@...ts.freedesktop.org
Cc: freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Rob Clark <robin.clark@....qualcomm.com>,
        Stephan Gerhold <stephan.gerhold@...aro.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>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] drm/msm: Fix GEM free for imported dma-bufs

Imported dma-bufs also have obj->resv != &obj->_resv.  So we should
check both this condition in addition to flags for handling the
_NO_SHARE case.

Fixes this splat that was reported with IRIS video playback:

    ------------[ cut here ]------------
    WARNING: CPU: 3 PID: 2040 at drivers/gpu/drm/msm/msm_gem.c:1127 msm_gem_free_object+0x1f8/0x264 [msm]
    CPU: 3 UID: 1000 PID: 2040 Comm: .gnome-shell-wr Not tainted 6.17.0-rc7 #1 PREEMPT
    pstate: 81400005 (Nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
    pc : msm_gem_free_object+0x1f8/0x264 [msm]
    lr : msm_gem_free_object+0x138/0x264 [msm]
    sp : ffff800092a1bb30
    x29: ffff800092a1bb80 x28: ffff800092a1bce8 x27: ffffbc702dbdbe08
    x26: 0000000000000008 x25: 0000000000000009 x24: 00000000000000a6
    x23: ffff00083c72f850 x22: ffff00083c72f868 x21: ffff00087e69f200
    x20: ffff00087e69f330 x19: ffff00084d157ae0 x18: 0000000000000000
    x17: 0000000000000000 x16: ffffbc704bd46b80 x15: 0000ffffd0959540
    x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
    x11: ffffbc702e6cdb48 x10: 0000000000000000 x9 : 000000000000003f
    x8 : ffff800092a1ba90 x7 : 0000000000000000 x6 : 0000000000000020
    x5 : ffffbc704bd46c40 x4 : fffffdffe102cf60 x3 : 0000000000400032
    x2 : 0000000000020000 x1 : ffff00087e6978e8 x0 : ffff00087e6977e8
    Call trace:
     msm_gem_free_object+0x1f8/0x264 [msm] (P)
     drm_gem_object_free+0x1c/0x30 [drm]
     drm_gem_object_handle_put_unlocked+0x138/0x150 [drm]
     drm_gem_object_release_handle+0x5c/0xcc [drm]
     drm_gem_handle_delete+0x68/0xbc [drm]
     drm_gem_close_ioctl+0x34/0x40 [drm]
     drm_ioctl_kernel+0xc0/0x130 [drm]
     drm_ioctl+0x360/0x4e0 [drm]
     __arm64_sys_ioctl+0xac/0x104
     invoke_syscall+0x48/0x104
     el0_svc_common.constprop.0+0x40/0xe0
     do_el0_svc+0x1c/0x28
     el0_svc+0x34/0xec
     el0t_64_sync_handler+0xa0/0xe4
     el0t_64_sync+0x198/0x19c
    ---[ end trace 0000000000000000 ]---
    ------------[ cut here ]------------

Reported-by: Stephan Gerhold <stephan.gerhold@...aro.org>
Fixes: de651b6e040b ("drm/msm: Fix refcnt underflow in error path")
Signed-off-by: Rob Clark <robin.clark@....qualcomm.com>
---
 drivers/gpu/drm/msm/msm_gem.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 9f0f5b77f1bd..3aea9b493375 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -1121,12 +1121,16 @@ static void msm_gem_free_object(struct drm_gem_object *obj)
 		put_pages(obj);
 	}
 
-	if (obj->resv != &obj->_resv) {
+	/*
+	 * In error paths, we could end up here before msm_gem_new_handle()
+	 * has changed obj->resv to point to the shared resv.  In this case,
+	 * we don't want to drop a ref to the shared r_obj that we haven't
+	 * taken yet.
+	 */
+	if ((msm_obj->flags & MSM_BO_NO_SHARE) && (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);
 	}
-- 
2.51.0