[Intel-gfx] [PATCH 1/3] dma_resv: prime lockdep annotations
Daniel Vetter
daniel.vetter at ffwll.ch
Mon Nov 11 15:42:11 UTC 2019
On Mon, Nov 11, 2019 at 2:11 PM Steven Price <steven.price at arm.com> wrote:
>
> 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.
Uh, so _that_ was what the 0day thing was all about, I totally misread
that completely. Thanks for the patch.
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Aside, do you need commit rights for pushing this kind of stuff?
-Daniel
>
> 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
>
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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