[Intel-gfx] [PATCH] drm/i915: Switch obj->mm.lock lockdep annotations on its head
Tang, CQ
cq.tang at intel.com
Sat Aug 17 05:32:27 UTC 2019
> -----Original Message-----
> From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch]
> Sent: Friday, August 16, 2019 3:08 PM
> To: Tang, CQ <cq.tang at intel.com>
> Cc: Intel Graphics Development <intel-gfx at lists.freedesktop.org>; Chris
> Wilson <chris at chris-wilson.co.uk>; Ursulin, Tvrtko
> <tvrtko.ursulin at intel.com>; Joonas Lahtinen
> <joonas.lahtinen at linux.intel.com>; Vetter, Daniel <daniel.vetter at intel.com>
> Subject: Re: [PATCH] drm/i915: Switch obj->mm.lock lockdep annotations on
> its head
>
> On Fri, Aug 16, 2019 at 9:23 PM Tang, CQ <cq.tang at intel.com> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch]
> > > Sent: Friday, August 16, 2019 11:24 AM
> > > To: Intel Graphics Development <intel-gfx at lists.freedesktop.org>
> > > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>; Chris Wilson
> > > <chris at chris- wilson.co.uk>; Tang, CQ <cq.tang at intel.com>; Ursulin,
> > > Tvrtko <tvrtko.ursulin at intel.com>; Joonas Lahtinen
> > > <joonas.lahtinen at linux.intel.com>; Vetter, Daniel
> > > <daniel.vetter at intel.com>
> > > Subject: [PATCH] drm/i915: Switch obj->mm.lock lockdep annotations
> > > on its head
> > >
> > > The trouble with having a plain nesting flag for locks which do not
> > > naturally nest (unlike block devices and their partitions, which is
> > > the original motivation for nesting levels) is that lockdep will
> > > never spot a true deadlock if you screw up.
> > >
> > > This patch is an attempt at trying better, by highlighting a bit
> > > more the actual nature of the nesting that's going on. Essentially
> > > we have two kinds of
> > > objects:
> > >
> > > - objects without pages allocated, which cannot be on any lru and are
> > > hence inaccessible to the shrinker.
> > >
> > > - objects which have pages allocated, which are on an lru, and which
> > > the shrinker can decide to throw out.
> > >
> > > For the former type of object, memory allcoations while holding
> > > obj->mm.lock are permissible. For the latter they are not. And
> > > get/put_pages transitions between the two types of objects.
> > >
> > > This is still not entirely fool-proof since the rules might chance.
> > > But as long as we run such a code ever at runtime lockdep should be
> > > able to observe the inconsistency and complain (like with any other
> > > lockdep class that we've split up in multiple classes). But there are a few
> clear benefits:
> > >
> > > - We can drop the nesting flag parameter from
> > > __i915_gem_object_put_pages, because that function by definition is
> > > never going allocate memory, and calling it on an object which
> > > doesn't have its pages allocated would be a bug.
> > >
> > > - We strictly catch more bugs, since there's not only one place in the
> > > entire tree which is annotated with the special class. All the
> > > other places that had explicit lockdep nesting annotations we're now
> > > going to leave up to lockdep again.
> > >
> > > - Specifically this catches stuff like calling get_pages from
> > > put_pages (which isn't really a good idea, if we can call put_pages
> > > so could the shrinker). I've seen patches do exactly that.
> > >
> > > Of course I fully expect CI will show me for the fool I am with this
> > > one here :-)
> > >
> > > v2: There can only be one (lockdep only has a cache for the first
> > > subclass, not for deeper ones, and we don't want to make these locks
> > > even slower). Still separate enums for better documentation.
> > >
> > > Real fix: don forget about phys objs and pin_map(), and fix the
> > > shrinker to have the right annotations ... silly me.
> > >
> > > v3: Forgot usertptr too ...
> > >
> > > v4: Improve comment for pages_pin_count, drop the IMPORTANT
> comment
> > > and instead prime lockdep (Chris).
> > >
> > > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > > Cc: "Tang, CQ" <cq.tang at intel.com>
> > > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > > ---
> > > drivers/gpu/drm/i915/gem/i915_gem_object.c | 13 ++++++++++++-
> > > drivers/gpu/drm/i915/gem/i915_gem_object.h | 16
> +++++++++++++---
> > > drivers/gpu/drm/i915/gem/i915_gem_object_types.h | 6 +++++-
> > > drivers/gpu/drm/i915/gem/i915_gem_pages.c | 9 ++++-----
> > > drivers/gpu/drm/i915/gem/i915_gem_phys.c | 2 +-
> > > drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 5 ++---
> > > drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 4 ++--
> > > drivers/gpu/drm/i915/gem/selftests/huge_pages.c | 12 ++++++------
> > > 8 files changed, 45 insertions(+), 22 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c
> > > b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> > > index 3929c3a6b281..d01258b175f5 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> > > @@ -22,6 +22,8 @@
> > > *
> > > */
> > >
> > > +#include <linux/sched/mm.h>
> > > +
> > > #include "display/intel_frontbuffer.h"
> > > #include "gt/intel_gt.h"
> > > #include "i915_drv.h"
> > > @@ -61,6 +63,15 @@ void i915_gem_object_init(struct
> > > drm_i915_gem_object *obj, {
> > > mutex_init(&obj->mm.lock);
> > >
> > > + if (IS_ENABLED(CONFIG_LOCKDEP)) {
> > > + mutex_lock_nested(&obj->mm.lock,
> > > I915_MM_GET_PAGES);
> > > + fs_reclaim_acquire(GFP_KERNEL);
> > > + might_lock(&obj->mm.lock);
> > > + fs_reclaim_release(GFP_KERNEL);
> > > + mutex_unlock(&obj->mm.lock);
> > > + }
> > > +
> > > +
> > > spin_lock_init(&obj->vma.lock);
> > > INIT_LIST_HEAD(&obj->vma.list);
> > >
> > > @@ -191,7 +202,7 @@ static void __i915_gem_free_objects(struct
> > > drm_i915_private *i915,
> > > GEM_BUG_ON(!list_empty(&obj->lut_list));
> > >
> > > atomic_set(&obj->mm.pages_pin_count, 0);
> > > - __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
> > > + __i915_gem_object_put_pages(obj);
> > > GEM_BUG_ON(i915_gem_object_has_pages(obj));
> > > bitmap_free(obj->bit_17);
> > >
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > > b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > > index 3714cf234d64..5ce511ca7fa8 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > > @@ -281,11 +281,21 @@ i915_gem_object_unpin_pages(struct
> > > drm_i915_gem_object *obj)
> > >
> > > enum i915_mm_subclass { /* lockdep subclass for obj-
> > > >mm.lock/struct_mutex */
> > > I915_MM_NORMAL = 0,
> > > - I915_MM_SHRINKER /* called "recursively" from direct-reclaim-
> > > esque */
> > > + /*
> > > + * Only used by struct_mutex, when called "recursively" from
> > > + * direct-reclaim-esque. Safe because there is only every one
> > > + * struct_mutex in the entire system. */
> > > + I915_MM_SHRINKER = 1,
> > > + /*
> > > + * Used for obj->mm.lock when allocating pages. Safe because
> > > + the
> > > object
> > > + * isn't yet on any LRU, and therefore the shrinker can't deadlock on
> > > + * it. As soon as the object has pages, obj->mm.lock nests within
> > > + * fs_reclaim.
> > > + */
> > > + I915_MM_GET_PAGES = 1,
> >
> > If both have the same value, why bother to use two names? Can we use a
> single generic name?
>
> They're two totally different things. The commit message explains why I've
> picked the same value for both.
>
> I mean you're essentially arguing (thought to the extreme conclusion at least)
> that every #define SOMETHING 1 should be replaced by the same define.
> That defeats the point of having meaningful names for values ...
It makes some sense, isn't it better to define two sets of enum, one for 'struct_mutex', one for obj->mm.lock ? Or do both still have some connection ?
--CQ
>
> Cheers, Daniel
>
> >
> > --CQ
> >
> > > };
> > >
> > > -int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
> > > - enum i915_mm_subclass subclass);
> > > +int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj);
> > > void i915_gem_object_truncate(struct drm_i915_gem_object *obj);
> > > void i915_gem_object_writeback(struct drm_i915_gem_object *obj);
> > >
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > > b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > > index d474c6ac4100..42d114f27d1a 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > > @@ -157,7 +157,11 @@ struct drm_i915_gem_object {
> > > unsigned int pin_global;
> > >
> > > struct {
> > > - struct mutex lock; /* protects the pages and their use */
> > > + /*
> > > + * Protects the pages and their use. Do not use directly, but
> > > + * instead go through the pin/unpin interfaces.
> > > + */
> > > + struct mutex lock;
> > > atomic_t pages_pin_count;
> > >
> > > struct sg_table *pages; diff --git
> > > a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> > > b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> > > index 18f0ce0135c1..202526e8910f 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> > > @@ -101,7 +101,7 @@ int __i915_gem_object_get_pages(struct
> > > drm_i915_gem_object *obj) {
> > > int err;
> > >
> > > - err = mutex_lock_interruptible(&obj->mm.lock);
> > > + err = mutex_lock_interruptible_nested(&obj->mm.lock,
> > > +I915_MM_GET_PAGES);
> > > if (err)
> > > return err;
> > >
> > > @@ -179,8 +179,7 @@ __i915_gem_object_unset_pages(struct
> > > drm_i915_gem_object *obj)
> > > return pages;
> > > }
> > >
> > > -int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
> > > - enum i915_mm_subclass subclass)
> > > +int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
> > > {
> > > struct sg_table *pages;
> > > int err;
> > > @@ -191,7 +190,7 @@ int __i915_gem_object_put_pages(struct
> > > drm_i915_gem_object *obj,
> > > GEM_BUG_ON(atomic_read(&obj->bind_count));
> > >
> > > /* May be called by shrinker from within get_pages() (on
> > > another bo) */
> > > - mutex_lock_nested(&obj->mm.lock, subclass);
> > > + mutex_lock(&obj->mm.lock);
> > > if (unlikely(atomic_read(&obj->mm.pages_pin_count))) {
> > > err = -EBUSY;
> > > goto unlock;
> > > @@ -285,7 +284,7 @@ void *i915_gem_object_pin_map(struct
> > > drm_i915_gem_object *obj,
> > > if (unlikely(!i915_gem_object_has_struct_page(obj)))
> > > return ERR_PTR(-ENXIO);
> > >
> > > - err = mutex_lock_interruptible(&obj->mm.lock);
> > > + err = mutex_lock_interruptible_nested(&obj->mm.lock,
> > > +I915_MM_GET_PAGES);
> > > if (err)
> > > return ERR_PTR(err);
> > >
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_phys.c
> > > b/drivers/gpu/drm/i915/gem/i915_gem_phys.c
> > > index 102fd7a23d3d..209925be8a76 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_phys.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_phys.c
> > > @@ -156,7 +156,7 @@ int i915_gem_object_attach_phys(struct
> > > drm_i915_gem_object *obj, int align)
> > > if (err)
> > > return err;
> > >
> > > - mutex_lock(&obj->mm.lock);
> > > + mutex_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES);
> > >
> > > if (obj->mm.madv != I915_MADV_WILLNEED) {
> > > err = -EFAULT;
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> > > b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> > > index edd21d14e64f..0b0d6e27b996 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> > > @@ -98,7 +98,7 @@ static bool unsafe_drop_pages(struct
> > > drm_i915_gem_object *obj,
> > > flags = I915_GEM_OBJECT_UNBIND_ACTIVE;
> > >
> > > if (i915_gem_object_unbind(obj, flags) == 0)
> > > - __i915_gem_object_put_pages(obj, I915_MM_SHRINKER);
> > > + __i915_gem_object_put_pages(obj);
> > >
> > > return !i915_gem_object_has_pages(obj); } @@ -254,8 +254,7 @@
> > > i915_gem_shrink(struct drm_i915_private *i915,
> > >
> > > if (unsafe_drop_pages(obj, shrink)) {
> > > /* May arrive from get_pages on
> > > another bo */
> > > - mutex_lock_nested(&obj->mm.lock,
> > > - I915_MM_SHRINKER);
> > > + mutex_lock(&obj->mm.lock);
> > > if (!i915_gem_object_has_pages(obj)) {
> > > try_to_writeback(obj, shrink);
> > > count += obj->base.size >>
> > > PAGE_SHIFT; diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> > > b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> > > index 70dc506a5426..f3b3bc7c32cb 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> > > @@ -158,7 +158,7 @@ userptr_mn_invalidate_range_start(struct
> > > mmu_notifier *_mn,
> > > ret = i915_gem_object_unbind(obj,
> > >
> > > I915_GEM_OBJECT_UNBIND_ACTIVE);
> > > if (ret == 0)
> > > - ret = __i915_gem_object_put_pages(obj,
> > > I915_MM_SHRINKER);
> > > + ret = __i915_gem_object_put_pages(obj);
> > > i915_gem_object_put(obj);
> > > if (ret)
> > > goto unlock;
> > > @@ -514,7 +514,7 @@ __i915_gem_userptr_get_pages_worker(struct
> > > work_struct *_work)
> > > }
> > > }
> > >
> > > - mutex_lock(&obj->mm.lock);
> > > + mutex_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES);
> > > if (obj->userptr.work == &work->work) {
> > > struct sg_table *pages = ERR_PTR(ret);
> > >
> > > diff --git a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
> > > b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
> > > index 6cbd4a668c9a..df586035c33e 100644
> > > --- a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
> > > +++ b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
> > > @@ -562,7 +562,7 @@ static int igt_mock_ppgtt_misaligned_dma(void
> *arg)
> > > i915_vma_close(vma);
> > >
> > > i915_gem_object_unpin_pages(obj);
> > > - __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
> > > + __i915_gem_object_put_pages(obj);
> > > i915_gem_object_put(obj);
> > > }
> > >
> > > @@ -590,7 +590,7 @@ static void close_object_list(struct list_head
> > > *objects,
> > >
> > > list_del(&obj->st_link);
> > > i915_gem_object_unpin_pages(obj);
> > > - __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
> > > + __i915_gem_object_put_pages(obj);
> > > i915_gem_object_put(obj);
> > > }
> > > }
> > > @@ -860,7 +860,7 @@ static int igt_mock_ppgtt_64K(void *arg)
> > > i915_vma_close(vma);
> > >
> > > i915_gem_object_unpin_pages(obj);
> > > - __i915_gem_object_put_pages(obj,
> > > I915_MM_NORMAL);
> > > + __i915_gem_object_put_pages(obj);
> > > i915_gem_object_put(obj);
> > > }
> > > }
> > > @@ -1268,7 +1268,7 @@ static int igt_ppgtt_exhaust_huge(void *arg)
> > > }
> > >
> > > i915_gem_object_unpin_pages(obj);
> > > - __i915_gem_object_put_pages(obj,
> > > I915_MM_NORMAL);
> > > + __i915_gem_object_put_pages(obj);
> > > i915_gem_object_put(obj);
> > > }
> > > }
> > > @@ -1330,7 +1330,7 @@ static int igt_ppgtt_internal_huge(void *arg)
> > > }
> > >
> > > i915_gem_object_unpin_pages(obj);
> > > - __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
> > > + __i915_gem_object_put_pages(obj);
> > > i915_gem_object_put(obj);
> > > }
> > >
> > > @@ -1399,7 +1399,7 @@ static int igt_ppgtt_gemfs_huge(void *arg)
> > > }
> > >
> > > i915_gem_object_unpin_pages(obj);
> > > - __i915_gem_object_put_pages(obj, I915_MM_NORMAL);
> > > + __i915_gem_object_put_pages(obj);
> > > i915_gem_object_put(obj);
> > > }
> > >
> > > --
> > > 2.23.0.rc1
> >
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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