[PATCH 1/3] dma_resv: prime lockdep annotations
Steven Price
steven.price at arm.com
Mon Nov 11 13:11:20 UTC 2019
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 at kernel.org>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: Rob Herring <robh at kernel.org>
> Cc: Tomeu Vizoso <tomeu.vizoso at collabora.com>
> Cc: Eric Anholt <eric at anholt.net>
> Cc: Dave Airlie <airlied at redhat.com>
> Cc: Gerd Hoffmann <kraxel at redhat.com>
> Cc: Ben Skeggs <bskeggs at redhat.com>
> Cc: "VMware Graphics" <linux-graphics-maintainer at vmware.com>
> Cc: Thomas Hellstrom <thellstrom at vmware.com>
> Reviewed-by: Christian König <christian.koenig at amd.com>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> Tested-by: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Daniel Vetter <daniel.vetter at 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 at 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 at 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
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