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Thu, 07 May 2026 23:57:30 -0700 (PDT) Received: from aegis ([2001:fd8:4d01:3602:5317:86f3:5298:5270]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2baf1ead938sm10650785ad.73.2026.05.07.23.57.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 May 2026 23:57:29 -0700 (PDT) From: Daniel J Blueman To: Rob Clark , Dmitry Baryshkov , Abhinav Kumar , Jessica Zhang , Sean Paul , Marijn Suijten , David Airlie , Simona Vetter , Antonino Maniscalco Cc: Daniel J Blueman , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH] drm/msm: Fix shrinker deadlock Date: Fri, 8 May 2026 14:57:21 +0800 Message-ID: <20260508065722.18785-1-daniel@quora.org> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit With PROVE_LOCKING on an Snapdragon X1 and VM reclaim pressure, we see: """ kswapd0/121 is trying to acquire lock: ffff800080ed3800 (reservation_ww_class_acquire){+.+.}-{0:0}, at: msm_gem_shrinker_scan (drivers/gpu/drm/msm/msm_gem_shrinker.c:189) but task is already holding lock: ffffbf4ddb44ca40 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat (mm/vmscan.c:7236 (discriminator 2)) which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (fs_reclaim){+.+.}-{0:0}: lock_acquire (kernel/locking/lockdep.c:5868 kernel/locking/lockdep.c:5825) fs_reclaim_acquire (mm/page_alloc.c:4325 mm/page_alloc.c:4339) dma_resv_lockdep (drivers/dma-buf/dma-resv.c:798) do_one_initcall (init/main.c:1392) kernel_init_freeable (init/main.c:1454 (discriminator 1) init/main.c:1470 (discriminator 1) init/main.c:1490 (discriminator 1) init/main.c:1703 (discriminator 1)) kernel_init (init/main.c:1593) ret_from_fork (arch/arm64/kernel/entry.S:858) -> #1 (reservation_ww_class_mutex){+.+.}-{4:4}: lock_acquire (kernel/locking/lockdep.c:5868 kernel/locking/lockdep.c:5825) dma_resv_lockdep (./include/linux/ww_mutex.h:164 (discriminator 1) drivers/dma-buf/dma-resv.c:791 (discriminator 1)) do_one_initcall (init/main.c:1392) kernel_init_freeable (init/main.c:1454 (discriminator 1) init/main.c:1470 (discriminator 1) init/main.c:1490 (discriminator 1) init/main.c:1703 (discriminator 1)) kernel_init (init/main.c:1593) ret_from_fork (arch/arm64/kernel/entry.S:858) -> #0 (reservation_ww_class_acquire){+.+.}-{0:0}: check_prev_add (kernel/locking/lockdep.c:3165) __lock_acquire (kernel/locking/lockdep.c:3284 kernel/locking/lockdep.c:3908 kernel/locking/lockdep.c:5237) lock_acquire (kernel/locking/lockdep.c:5868 kernel/locking/lockdep.c:5825) drm_gem_lru_scan (./include/linux/ww_mutex.h:163 (discriminator 1) drivers/gpu/drm/drm_gem.c:1681 (discriminator 1)) msm_gem_shrinker_scan (drivers/gpu/drm/msm/msm_gem_shrinker.c:189) do_shrink_slab (mm/shrinker.c:436) shrink_slab (mm/shrinker.c:667) shrink_one (mm/vmscan.c:5071) shrink_node (mm/vmscan.c:5132 mm/vmscan.c:5210 mm/vmscan.c:6198) balance_pgdat (mm/vmscan.c:7052 mm/vmscan.c:7228) kswapd (mm/vmscan.c:7501) kthread (kernel/kthread.c:436) ret_from_fork (arch/arm64/kernel/entry.S:858) other info that might help us debug this: Chain exists of: reservation_ww_class_acquire --> reservation_ww_class_mutex --> fs_reclaim """ kswapd0 holding fs_reclaim calls the MSM shrinker, which calls dma_resv_lock. This in turn acquires fs_reclaim. Fix this deadlock by using dma_resv_trylock() instead, dropping the subsequently unused passed wait-wound lock 'ticket'. Cc: stable@vger.kernel.org Signed-off-by: Daniel J Blueman Fixes: fe4952b5f27c ("drm/msm: Convert vm locking") --- drivers/gpu/drm/msm/msm_gem_shrinker.c | 34 ++++++++++---------------- 1 file changed, 13 insertions(+), 21 deletions(-) diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c index 31fa51a44f86..5320ef57dd90 100644 --- a/drivers/gpu/drm/msm/msm_gem_shrinker.c +++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c @@ -43,8 +43,7 @@ msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc) } static bool -with_vm_locks(struct ww_acquire_ctx *ticket, - void (*fn)(struct drm_gem_object *obj), +with_vm_locks(void (*fn)(struct drm_gem_object *obj), struct drm_gem_object *obj) { /* @@ -52,7 +51,7 @@ with_vm_locks(struct ww_acquire_ctx *ticket, * success paths */ struct drm_gpuvm_bo *vm_bo, *last_locked = NULL; - int ret = 0; + bool locked = true; drm_gem_for_each_gpuvm_bo (vm_bo, obj) { struct dma_resv *resv = drm_gpuvm_resv(vm_bo->vm); @@ -60,23 +59,14 @@ with_vm_locks(struct ww_acquire_ctx *ticket, if (resv == obj->resv) continue; - ret = dma_resv_lock(resv, ticket); - /* - * Since we already skip the case when the VM and obj - * share a resv (ie. _NO_SHARE objs), we don't expect - * to hit a double-locking scenario... which the lock - * unwinding cannot really cope with. + * dma_resv_lock can't be used due to acquiring 'ticket' before the + * fs_reclaim lock, which is held in shrinker context */ - WARN_ON(ret == -EALREADY); - - /* - * Don't bother with slow-lock / backoff / retry sequence, - * if we can't get the lock just give up and move on to - * the next object. - */ - if (ret) + if (!dma_resv_trylock(resv)) { + locked = false; goto out_unlock; + } /* * Hold a ref to prevent the vm_bo from being freed @@ -108,7 +98,7 @@ with_vm_locks(struct ww_acquire_ctx *ticket, } } - return ret == 0; + return locked; } static bool @@ -120,7 +110,7 @@ purge(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket) if (msm_gem_active(obj)) return false; - return with_vm_locks(ticket, msm_gem_purge, obj); + return with_vm_locks(msm_gem_purge, obj); } static bool @@ -164,7 +154,6 @@ static unsigned long msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc) { struct msm_drm_private *priv = shrinker->private_data; - struct ww_acquire_ctx ticket; struct { struct drm_gem_lru *lru; bool (*shrink)(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket); @@ -185,11 +174,14 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc) for (unsigned i = 0; (nr > 0) && (i < ARRAY_SIZE(stages)); i++) { if (!stages[i].cond) continue; + /* + * 'ticket' not needed on trylock paths + */ stages[i].freed = drm_gem_lru_scan(stages[i].lru, nr, &stages[i].remaining, stages[i].shrink, - &ticket); + NULL); nr -= stages[i].freed; freed += stages[i].freed; remaining += stages[i].remaining; -- 2.53.0