On 19/08/2019 17:12, Rob Herring wrote:
> 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@xxxxxxxxxxxxxxx>
> Cc: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
> Cc: Sean Paul <sean@xxxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
Seems reasonable, like you state I don't think this can actually happen,
but keeping lockdep happy is a good idea.
Reviewed-by: Steven Price <steven.price@xxxxxxx>
Steve
> ---
> 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,
>
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel
