From: Rob Herring <robh@kernel.org>
To: dri-devel@lists.freedesktop.org
Cc: Maxime Ripard <maxime.ripard@bootlin.com>,
Tomeu Vizoso <tomeu.vizoso@collabora.com>,
David Airlie <airlied@linux.ie>, Sean Paul <sean@poorly.run>,
Steven Price <steven.price@arm.com>,
Boris Brezillon <boris.brezillon@collabora.com>,
Robin Murphy <robin.murphy@arm.com>
Subject: [PATCH 2/4] drm/shmem: Use mutex_trylock in drm_gem_shmem_purge
Date: Mon, 19 Aug 2019 11:12:02 -0500 [thread overview]
Message-ID: <20190819161204.3106-3-robh@kernel.org> (raw)
In-Reply-To: <20190819161204.3106-1-robh@kernel.org>
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 <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Rob Herring <robh@kernel.org>
---
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,
--
2.20.1
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next prev parent reply other threads:[~2019-08-19 16:12 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 16:12 [PATCH 0/4] panfrost: Locking fixes Rob Herring
2019-08-19 16:12 ` [PATCH 1/4] drm/shmem: Do dma_unmap_sg before purging pages Rob Herring
2019-08-22 13:27 ` Steven Price
2019-08-19 16:12 ` Rob Herring [this message]
2019-08-20 9:05 ` [PATCH 2/4] drm/shmem: Use mutex_trylock in drm_gem_shmem_purge Daniel Vetter
2019-08-20 12:35 ` Rob Herring
2019-08-21 8:23 ` Daniel Vetter
2019-08-21 16:03 ` Rob Herring
2019-08-21 16:32 ` Daniel Vetter
2019-08-22 13:28 ` Steven Price
2019-08-19 16:12 ` [PATCH 3/4] drm/panfrost: Fix shrinker lockdep issues using drm_gem_shmem_purge() Rob Herring
2019-08-22 13:23 ` Steven Price
2019-08-19 16:12 ` [PATCH 4/4] drm/panfrost: Fix sleeping while atomic in panfrost_gem_open Rob Herring
2019-08-22 14:58 ` Steven Price
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