Re: [PATCH 1/3] dma_resv: prime lockdep annotations

[Steven Price <steven.price@arm.com>]

On 04/11/2019 17:37, Daniel Vetter wrote:
> Full audit of everyone:
> 
> - i915, radeon, amdgpu should be clean per their maintainers.
> 
> - vram helpers should be fine, they don't do command submission, so
>   really no business holding struct_mutex while doing copy_*_user. But
>   I haven't checked them all.
> 
> - panfrost seems to dma_resv_lock only in panfrost_job_push, which
>   looks clean.
> 
> - v3d holds dma_resv locks in the tail of its v3d_submit_cl_ioctl(),
>   copying from/to userspace happens all in v3d_lookup_bos which is
>   outside of the critical section.
> 
> - vmwgfx has a bunch of ioctls that do their own copy_*_user:
>   - vmw_execbuf_process: First this does some copies in
>     vmw_execbuf_cmdbuf() and also in the vmw_execbuf_process() itself.
>     Then comes the usual ttm reserve/validate sequence, then actual
>     submission/fencing, then unreserving, and finally some more
>     copy_to_user in vmw_execbuf_copy_fence_user. Glossing over tons of
>     details, but looks all safe.
>   - vmw_fence_event_ioctl: No ttm_reserve/dma_resv_lock anywhere to be
>     seen, seems to only create a fence and copy it out.
>   - a pile of smaller ioctl in vmwgfx_ioctl.c, no reservations to be
>     found there.
>   Summary: vmwgfx seems to be fine too.
> 
> - virtio: There's virtio_gpu_execbuffer_ioctl, which does all the
>   copying from userspace before even looking up objects through their
>   handles, so safe. Plus the getparam/getcaps ioctl, also both safe.
> 
> - qxl only has qxl_execbuffer_ioctl, which calls into
>   qxl_process_single_command. There's a lovely comment before the
>   __copy_from_user_inatomic that the slowpath should be copied from
>   i915, but I guess that never happened. Try not to be unlucky and get
>   your CS data evicted between when it's written and the kernel tries
>   to read it. The only other copy_from_user is for relocs, but those
>   are done before qxl_release_reserve_list(), which seems to be the
>   only thing reserving buffers (in the ttm/dma_resv sense) in that
>   code. So looks safe.
> 
> - A debugfs file in nouveau_debugfs_pstate_set() and the usif ioctl in
>   usif_ioctl() look safe. nouveau_gem_ioctl_pushbuf() otoh breaks this
>   everywhere and needs to be fixed up.
> 
> v2: Thomas pointed at that vmwgfx calls dma_resv_init while it holds a
> dma_resv lock of a different object already. Christian mentioned that
> ttm core does this too for ghost objects. intel-gfx-ci highlighted
> that i915 has similar issues.
> 
> Unfortunately we can't do this in the usual module init functions,
> because kernel threads don't have an ->mm - we have to wait around for
> some user thread to do this.
> 
> Solution is to spawn a worker (but only once). It's horrible, but it
> works.
> 
> v3: We can allocate mm! (Chris). Horrible worker hack out, clean
> initcall solution in.
> 
> v4: Annotate with __init (Rob Herring)
> 
> Cc: Rob Herring <robh@kernel.org>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Eric Anholt <eric@anholt.net>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Ben Skeggs <bskeggs@redhat.com>
> Cc: "VMware Graphics" <linux-graphics-maintainer@vmware.com>
> Cc: Thomas Hellstrom <thellstrom@vmware.com>
> Reviewed-by: Christian König <christian.koenig@amd.com>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/dma-buf/dma-resv.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index 709002515550..a05ff542be22 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -34,6 +34,7 @@
>  
>  #include <linux/dma-resv.h>
>  #include <linux/export.h>
> +#include <linux/sched/mm.h>
>  
>  /**
>   * DOC: Reservation Object Overview
> @@ -95,6 +96,29 @@ static void dma_resv_list_free(struct dma_resv_list *list)
>  	kfree_rcu(list, rcu);
>  }
>  
> +#if IS_ENABLED(CONFIG_LOCKDEP)
> +static void __init dma_resv_lockdep(void)
> +{
> +	struct mm_struct *mm = mm_alloc();
> +	struct dma_resv obj;
> +
> +	if (!mm)
> +		return;
> +
> +	dma_resv_init(&obj);
> +
> +	down_read(&mm->mmap_sem);
> +	ww_mutex_lock(&obj.lock, NULL);
> +	fs_reclaim_acquire(GFP_KERNEL);
> +	fs_reclaim_release(GFP_KERNEL);
> +	ww_mutex_unlock(&obj.lock);
> +	up_read(&mm->mmap_sem);
> +	

Nit: trailing whitespace

> +	mmput(mm);
> +}
> +subsys_initcall(dma_resv_lockdep);

This expects a function returning int, but dma_resv_lockdep() is void.
Causing:

drivers/dma-buf/dma-resv.c:119:17: error: initialization of ‘initcall_t’
{aka ‘int (*)(void)’} from incompatible pointer type ‘void (*)(void)’
[-Werror=incompatible-pointer-types]
 subsys_initcall(dma_resv_lockdep);

The below fixes it for me.

Steve

----8<----
From d07ea81611ed6e4fb8cc290f42d23dbcca2da2f8 Mon Sep 17 00:00:00 2001
From: Steven Price <steven.price@arm.com>
Date: Mon, 11 Nov 2019 13:07:19 +0000
Subject: [PATCH] dma_resv: Correct return type of dma_resv_lockdep()

subsys_initcall() expects a function which returns 'int'. Fix
dma_resv_lockdep() so it returns an 'int' error code.

Fixes: b2a8116e2592 ("dma_resv: prime lockdep annotations")
Signed-off-by: Steven Price <steven.price@arm.com>
---
 drivers/dma-buf/dma-resv.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index a05ff542be22..9918a6e5cf91 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -97,13 +97,13 @@ static void dma_resv_list_free(struct dma_resv_list *list)
 }
 
 #if IS_ENABLED(CONFIG_LOCKDEP)
-static void __init dma_resv_lockdep(void)
+static int __init dma_resv_lockdep(void)
 {
 	struct mm_struct *mm = mm_alloc();
 	struct dma_resv obj;
 
 	if (!mm)
-		return;
+		return -ENOMEM;
 
 	dma_resv_init(&obj);
 
@@ -115,6 +115,8 @@ static void __init dma_resv_lockdep(void)
 	up_read(&mm->mmap_sem);
 	
 	mmput(mm);
+
+	return 0;
 }
 subsys_initcall(dma_resv_lockdep);
 #endif
-- 
2.20.1

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel