diff options
author | Daniel Vetter <daniel.vetter@ffwll.ch> | 2021-09-02 16:20:49 +0200 |
---|---|---|
committer | Daniel Vetter <daniel.vetter@ffwll.ch> | 2021-09-06 10:45:48 +0200 |
commit | 8cf97637ff8891be040bac37b96dd97e5996ca93 (patch) | |
tree | 9f8a6f4c73b6981176db8f2122ff9ceb46b24d10 /drivers/gpu/drm/i915/gem/i915_gem_context.c | |
parent | c238980efd3b35af70fc926066cf7440f50a97a9 (diff) |
drm/i915: Keep gem ctx->vm alive until the final put
The comment added in
commit b81dde719439c8f09bb61e742ed95bfc4b33946b
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date: Tue May 21 22:11:29 2019 +0100
drm/i915: Allow userspace to clone contexts on creation
and moved in
commit 27dbae8f36c1c25008b7885fc07c57054b7dfba3
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date: Wed Nov 6 09:13:12 2019 +0000
drm/i915/gem: Safely acquire the ctx->vm when copying
suggested that i915_address_space were at least intended to be managed
through SLAB_TYPESAFE_BY_RCU:
* This ppgtt may have be reallocated between
* the read and the kref, and reassigned to a third
* context. In order to avoid inadvertent sharing
* of this ppgtt with that third context (and not
* src), we have to confirm that we have the same
* ppgtt after passing through the strong memory
* barrier implied by a successful
* kref_get_unless_zero().
But extensive git history search has not brough any such reuse to
light.
What has come to light though is that ever since
commit 2850748ef8763ab46958e43a4d1c445f29eeb37d
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date: Fri Oct 4 14:39:58 2019 +0100
drm/i915: Pull i915_vma_pin under the vm->mutex
(yes this commit is earlier) the final i915_vma_put call has been
moved from i915_gem_context_free (now called _release) to
context_close, which means it's not actually safe anymore to access
the ctx->vm pointer without lock helds, because it might disappear at
any moment. Note that superficially things all still work, because the
i915_address_space is RCU protected since
commit b32fa811156328aea5a3c2ff05cc096490382456
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu Jun 20 19:37:05 2019 +0100
drm/i915/gtt: Defer address space cleanup to an RCU worker
except the very clever macro above (which is designed to protected
against object reuse due to SLAB_TYPESAFE_BY_RCU or similar tricks)
results in an endless loop if the refcount of the ctx->vm ever
permanently drops to 0. Which it totally now can.
Fix that by moving the final i915_vm_put to where it should be.
Note that i915_gem_context is rcu protected, but _only_ the final
kfree. This means anyone who chases a pointer to a gem ctx solely
under the protection can pretty only call kref_get_unless_zero(). This
seems to be pretty much the case, aside from a bunch of cases that
consult the scheduling information without any further protection.
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: "Thomas Hellström" <thomas.hellstrom@intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Fixes: 2850748ef876 ("drm/i915: Pull i915_vma_pin under the vm->mutex")
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210902142057.929669-3-daniel.vetter@ffwll.ch
Diffstat (limited to 'drivers/gpu/drm/i915/gem/i915_gem_context.c')
-rw-r--r-- | drivers/gpu/drm/i915/gem/i915_gem_context.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c index 5a053cf14948..12e2de1db1a2 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -990,6 +990,7 @@ static void i915_gem_context_release_work(struct work_struct *work) { struct i915_gem_context *ctx = container_of(work, typeof(*ctx), release_work); + struct i915_address_space *vm; trace_i915_context_free(ctx); GEM_BUG_ON(!i915_gem_context_is_closed(ctx)); @@ -997,6 +998,10 @@ static void i915_gem_context_release_work(struct work_struct *work) if (ctx->syncobj) drm_syncobj_put(ctx->syncobj); + vm = i915_gem_context_vm(ctx); + if (vm) + i915_vm_put(vm); + mutex_destroy(&ctx->engines_mutex); mutex_destroy(&ctx->lut_mutex); @@ -1220,8 +1225,15 @@ static void context_close(struct i915_gem_context *ctx) set_closed_name(ctx); vm = i915_gem_context_vm(ctx); - if (vm) + if (vm) { + /* i915_vm_close drops the final reference, which is a bit too + * early and could result in surprises with concurrent + * operations racing with thist ctx close. Keep a full reference + * until the end. + */ + i915_vm_get(vm); i915_vm_close(vm); + } ctx->file_priv = ERR_PTR(-EBADF); |