From 3392291fc509d8ad6e4ad90f15b0a193f721cbc9 Mon Sep 17 00:00:00 2001 From: Daniel J Blueman Date: Fri, 8 May 2026 14:57:21 +0800 Subject: [PATCH] drm/msm: Fix shrinker deadlock With PROVE_LOCKING on an Snapdragon X1 and VM reclaim pressure, we see: ====================================================== WARNING: possible circular locking dependency detected 7.0.0-debug+ #43 Tainted: G W ------------------------------------------------------ kswapd0/82 is trying to acquire lock: ffff800080ec3870 (reservation_ww_class_acquire){+.+.}-{0:0}, at: msm_gem_shrinker_scan+0x17c/0x400 [msm] but task is already holding lock: ffffc31709b263b8 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x88/0x988 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (fs_reclaim){+.+.}-{0:0}: __lock_acquire+0x4d0/0xad0 lock_acquire.part.0+0xc4/0x248 lock_acquire+0x8c/0x248 fs_reclaim_acquire+0xd0/0xf0 dma_resv_lockdep+0x224/0x348 do_one_initcall+0x84/0x5d0 do_initcalls+0x194/0x1d8 kernel_init_freeable+0x128/0x180 kernel_init+0x2c/0x160 ret_from_fork+0x10/0x20 -> #1 (reservation_ww_class_mutex){+.+.}-{4:4}: __lock_acquire+0x4d0/0xad0 lock_acquire.part.0+0xc4/0x248 lock_acquire+0x8c/0x248 dma_resv_lockdep+0x1a8/0x348 do_one_initcall+0x84/0x5d0 do_initcalls+0x194/0x1d8 kernel_init_freeable+0x128/0x180 kernel_init+0x2c/0x160 ret_from_fork+0x10/0x20 -> #0 (reservation_ww_class_acquire){+.+.}-{0:0}: check_prev_add+0x114/0x790 validate_chain+0x594/0x6f0 __lock_acquire+0x4d0/0xad0 lock_acquire.part.0+0xc4/0x248 lock_acquire+0x8c/0x248 drm_gem_lru_scan+0x1ac/0x440 msm_gem_shrinker_scan+0x17c/0x400 [msm] do_shrink_slab+0x150/0x4a0 shrink_slab+0x144/0x460 shrink_one+0x9c/0x1b0 shrink_many+0x27c/0x5c0 shrink_node+0x344/0x550 balance_pgdat+0x2c0/0x988 kswapd+0x11c/0x318 kthread+0x10c/0x128 ret_from_fork+0x10/0x20 other info that might help us debug this: Chain exists of: reservation_ww_class_acquire --> reservation_ww_class_mutex --> fs_reclaim Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(fs_reclaim); lock(reservation_ww_class_mutex); lock(fs_reclaim); lock(reservation_ww_class_acquire); *** DEADLOCK *** 1 lock held by kswapd0/82: #0: ffffc31709b263b8 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x88/0x988 stack backtrace: CPU: 4 UID: 0 PID: 82 Comm: kswapd0 Tainted: G W 7.0.0-debug+ #43 PREEMPT(full) Tainted: [W]=WARN Hardware name: LENOVO 21BX0016US/21BX0016US, BIOS N3HET94W (1.66 ) 09/15/2025 Call trace: show_stack+0x20/0x40 (C) dump_stack_lvl+0x9c/0xd0 dump_stack+0x18/0x30 print_circular_bug+0x114/0x120 check_noncircular+0x178/0x198 check_prev_add+0x114/0x790 validate_chain+0x594/0x6f0 __lock_acquire+0x4d0/0xad0 lock_acquire.part.0+0xc4/0x248 lock_acquire+0x8c/0x248 drm_gem_lru_scan+0x1ac/0x440 msm_gem_shrinker_scan+0x17c/0x400 [msm] do_shrink_slab+0x150/0x4a0 shrink_slab+0x144/0x460 shrink_one+0x9c/0x1b0 shrink_many+0x27c/0x5c0 shrink_node+0x344/0x550 balance_pgdat+0x2c0/0x988 kswapd+0x11c/0x318 kthread+0x10c/0x128 ret_from_fork+0x10/0x20 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") Patchwork: https://patchwork.freedesktop.org/patch/723564/ Message-ID: <20260508065722.18785-1-daniel@quora.org> [rob: fixup compile errors, replace lockdep splat with something legible] Signed-off-by: Rob Clark --- drivers/gpu/drm/msm/msm_gem_shrinker.c | 40 +++++++++++--------------- 1 file changed, 16 insertions(+), 24 deletions(-) diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c index 31fa51a44f86..6e39e4e578bb 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 @@ -108,11 +98,11 @@ with_vm_locks(struct ww_acquire_ctx *ticket, } } - return ret == 0; + return locked; } static bool -purge(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket) +purge(struct drm_gem_object *obj, struct ww_acquire_ctx *) { if (!is_purgeable(to_msm_bo(obj))) return false; @@ -120,11 +110,11 @@ 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 -evict(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket) +evict(struct drm_gem_object *obj, struct ww_acquire_ctx *) { if (is_unevictable(to_msm_bo(obj))) return false; @@ -132,7 +122,7 @@ evict(struct drm_gem_object *obj, struct ww_acquire_ctx *ticket) if (msm_gem_active(obj)) return false; - return with_vm_locks(ticket, msm_gem_evict, obj); + return with_vm_locks(msm_gem_evict, 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;