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[24.155.109.49]) by smtp.googlemail.com with ESMTPSA id c19sm4770584ioi.22.2019.08.19.09.12.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Aug 2019 09:12:08 -0700 (PDT) From: Rob Herring To: dri-devel@lists.freedesktop.org Subject: [PATCH 2/4] drm/shmem: Use mutex_trylock in drm_gem_shmem_purge Date: Mon, 19 Aug 2019 11:12:02 -0500 Message-Id: <20190819161204.3106-3-robh@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190819161204.3106-1-robh@kernel.org> References: <20190819161204.3106-1-robh@kernel.org> MIME-Version: 1.0 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Maxime Ripard , Tomeu Vizoso , David Airlie , Sean Paul , Steven Price , Boris Brezillon , Robin Murphy Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Lockdep reports a circular locking dependency with pages_lock taken in the shrinker callback. The deadlock can't actually happen with current users at least as a BO will never be purgeable when pages_lock is held. To be safe, let's use mutex_trylock() instead and bail if a BO is locked already. WARNING: possible circular locking dependency detected 5.3.0-rc1+ #100 Tainted: G L ------------------------------------------------------ kswapd0/171 is trying to acquire lock: 000000009b9823fd (&shmem->pages_lock){+.+.}, at: drm_gem_shmem_purge+0x20/0x40 but task is already holding lock: 00000000f82369b6 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x40 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (fs_reclaim){+.+.}: fs_reclaim_acquire.part.18+0x34/0x40 fs_reclaim_acquire+0x20/0x28 __kmalloc_node+0x6c/0x4c0 kvmalloc_node+0x38/0xa8 drm_gem_get_pages+0x80/0x1d0 drm_gem_shmem_get_pages+0x58/0xa0 drm_gem_shmem_get_pages_sgt+0x48/0xd0 panfrost_mmu_map+0x38/0xf8 [panfrost] panfrost_gem_open+0xc0/0xe8 [panfrost] drm_gem_handle_create_tail+0xe8/0x198 drm_gem_handle_create+0x3c/0x50 panfrost_gem_create_with_handle+0x70/0xa0 [panfrost] panfrost_ioctl_create_bo+0x48/0x80 [panfrost] drm_ioctl_kernel+0xb8/0x110 drm_ioctl+0x244/0x3f0 do_vfs_ioctl+0xbc/0x910 ksys_ioctl+0x78/0xa8 __arm64_sys_ioctl+0x1c/0x28 el0_svc_common.constprop.0+0x90/0x168 el0_svc_handler+0x28/0x78 el0_svc+0x8/0xc -> #0 (&shmem->pages_lock){+.+.}: __lock_acquire+0xa2c/0x1d70 lock_acquire+0xdc/0x228 __mutex_lock+0x8c/0x800 mutex_lock_nested+0x1c/0x28 drm_gem_shmem_purge+0x20/0x40 panfrost_gem_shrinker_scan+0xc0/0x180 [panfrost] do_shrink_slab+0x208/0x500 shrink_slab+0x10c/0x2c0 shrink_node+0x28c/0x4d8 balance_pgdat+0x2c8/0x570 kswapd+0x22c/0x638 kthread+0x128/0x130 ret_from_fork+0x10/0x18 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(fs_reclaim); lock(&shmem->pages_lock); lock(fs_reclaim); lock(&shmem->pages_lock); *** DEADLOCK *** 3 locks held by kswapd0/171: #0: 00000000f82369b6 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x40 #1: 00000000ceb37808 (shrinker_rwsem){++++}, at: shrink_slab+0xbc/0x2c0 #2: 00000000f31efa81 (&pfdev->shrinker_lock){+.+.}, at: panfrost_gem_shrinker_scan+0x34/0x180 [panfrost] Fixes: 17acb9f35ed7 ("drm/shmem: Add madvise state and purge helpers") Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Sean Paul Cc: David Airlie Cc: Daniel Vetter Signed-off-by: Rob Herring Reviewed-by: Steven Price --- drivers/gpu/drm/drm_gem_shmem_helper.c | 7 +++++-- include/drm/drm_gem_shmem_helper.h | 2 +- 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index 5423ec56b535..f5918707672f 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -415,13 +415,16 @@ void drm_gem_shmem_purge_locked(struct drm_gem_object *obj) } EXPORT_SYMBOL(drm_gem_shmem_purge_locked); -void drm_gem_shmem_purge(struct drm_gem_object *obj) +bool drm_gem_shmem_purge(struct drm_gem_object *obj) { struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj); - mutex_lock(&shmem->pages_lock); + if (!mutex_trylock(&shmem->pages_lock)) + return false; drm_gem_shmem_purge_locked(obj); mutex_unlock(&shmem->pages_lock); + + return true; } EXPORT_SYMBOL(drm_gem_shmem_purge); diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h index ce1600fdfc3e..01f514521687 100644 --- a/include/drm/drm_gem_shmem_helper.h +++ b/include/drm/drm_gem_shmem_helper.h @@ -134,7 +134,7 @@ static inline bool drm_gem_shmem_is_purgeable(struct drm_gem_shmem_object *shmem } void drm_gem_shmem_purge_locked(struct drm_gem_object *obj); -void drm_gem_shmem_purge(struct drm_gem_object *obj); +bool drm_gem_shmem_purge(struct drm_gem_object *obj); struct drm_gem_shmem_object * drm_gem_shmem_create_with_handle(struct drm_file *file_priv,