On 07/01/2020 11:15, Tvrtko Ursulin wrote:
On 22/12/2019 23:35, Chris Wilson wrote:
The only protection for intel_context.gem_cotext is granted by RCU, so
annotate it as a rcu protected pointer and carefully dereference it in
the few occasions we need to use it.
Fixes: 9f3ccd40acf4 ("drm/i915: Drop GEM context as a direct link from
i915_request")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Andi Shyti <andi.shyti@xxxxxxxxx>
---
drivers/gpu/drm/i915/gem/i915_gem_context.c | 5 ++-
drivers/gpu/drm/i915/gt/intel_context_types.h | 2 +-
drivers/gpu/drm/i915/gt/intel_reset.c | 26 +++++++++---
.../gpu/drm/i915/gt/intel_ring_submission.c | 2 +-
drivers/gpu/drm/i915/i915_gpu_error.c | 40 ++++++++++++-------
drivers/gpu/drm/i915/i915_request.c | 6 +--
drivers/gpu/drm/i915/i915_request.h | 8 ++++
7 files changed, 62 insertions(+), 27 deletions(-)
[snip]
static void engine_record_requests(struct intel_engine_cs *engine,
@@ -1298,28 +1304,34 @@ static void
error_record_engine_execlists(const struct intel_engine_cs *engine,
static bool record_context(struct drm_i915_error_context *e,
const struct i915_request *rq)
{
- const struct i915_gem_context *ctx = rq->context->gem_context;
+ struct i915_gem_context *ctx;
+ struct task_struct *task;
+ bool capture;
+ rcu_read_lock();
+ ctx = rcu_dereference(rq->context->gem_context);
+ if (ctx && !kref_get_unless_zero(&ctx->ref))
+ ctx = NULL;
+ rcu_read_unlock();
if (!ctx)
return false;
- if (ctx->pid) {
- struct task_struct *task;
-
- rcu_read_lock();
- task = pid_task(ctx->pid, PIDTYPE_PID);
- if (task) {
- strcpy(e->comm, task->comm);
- e->pid = task->pid;
- }
- rcu_read_unlock();
+ rcu_read_lock();
+ task = pid_task(ctx->pid, PIDTYPE_PID);
+ if (task) {
+ strcpy(e->comm, task->comm);
+ e->pid = task->pid;
}
+ rcu_read_unlock();
Why is this rcu_read_lock section needed? The first one obtained the
reference to the context so should be good.
Hmm pid_task() does:
...
first =
rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
lockdep_tasklist_lock_is_held());
...
Note, tasklist_lock_is_held.
Regards,
Tvrtko
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