From: Chris Wilson chris@chris-wilson.co.uk
commit 19b5f3b419a61808ff2713f1f30b8a88fe14ac9b upstream.
Mika spotted
<4>[17436.705441] general protection fault: 0000 [#1] PREEMPT SMP PTI <4>[17436.705447] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 5.5.0+ #1 <4>[17436.705449] Hardware name: System manufacturer System Product Name/Z170M-PLUS, BIOS 3805 05/16/2018 <4>[17436.705512] RIP: 0010:__execlists_submission_tasklet+0xc4d/0x16e0 [i915] <4>[17436.705516] Code: c5 4c 8d 60 e0 75 17 e9 8c 07 00 00 49 8b 44 24 20 49 39 c5 4c 8d 60 e0 0f 84 7a 07 00 00 49 8b 5c 24 08 49 8b 87 80 00 00 00 <48> 39 83 d8 fe ff ff 75 d9 48 8b 83 88 fe ff ff a8 01 0f 84 b6 05 <4>[17436.705518] RSP: 0018:ffffc9000012ce80 EFLAGS: 00010083 <4>[17436.705521] RAX: ffff88822ae42000 RBX: 5a5a5a5a5a5a5a5a RCX: dead000000000122 <4>[17436.705523] RDX: ffff88822ae42588 RSI: ffff8881e32a7908 RDI: ffff8881c429fd48 <4>[17436.705525] RBP: ffffc9000012cf00 R08: ffff88822ae42588 R09: 00000000fffffffe <4>[17436.705527] R10: ffff8881c429fb80 R11: 00000000a677cf08 R12: ffff8881c42a0aa8 <4>[17436.705529] R13: ffff8881c429fd38 R14: ffff88822ae42588 R15: ffff8881c429fb80 <4>[17436.705532] FS: 0000000000000000(0000) GS:ffff88822ed00000(0000) knlGS:0000000000000000 <4>[17436.705534] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 <4>[17436.705536] CR2: 00007f858c76d000 CR3: 0000000005610003 CR4: 00000000003606e0 <4>[17436.705538] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 <4>[17436.705540] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 <4>[17436.705542] Call Trace: <4>[17436.705545] <IRQ> <4>[17436.705603] execlists_submission_tasklet+0xc0/0x130 [i915]
which is us consuming a partially initialised new waiter in defer_requests(). We can prevent this by initialising the i915_dependency prior to making it visible, and since we are using a concurrent list_add/iterator mark them up to the compiler.
Fixes: 8ee36e048c98 ("drm/i915/execlists: Minimalistic timeslicing") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Mika Kuoppala mika.kuoppala@linux.intel.com Reviewed-by: Mika Kuoppala mika.kuoppala@linux.intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20200206204915.2636606-2-chris... (cherry picked from commit f14f27b1663269a81ed62d3961fe70250a1a0623) Signed-off-by: Jani Nikula jani.nikula@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/gpu/drm/i915/gt/intel_lrc.c | 7 ++++++- drivers/gpu/drm/i915/i915_scheduler.c | 6 ++++-- 2 files changed, 10 insertions(+), 3 deletions(-)
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c @@ -933,6 +933,11 @@ last_active(const struct intel_engine_ex return *last; }
+#define for_each_waiter(p__, rq__) \ + list_for_each_entry_lockless(p__, \ + &(rq__)->sched.waiters_list, \ + wait_link) + static void defer_request(struct i915_request *rq, struct list_head * const pl) { LIST_HEAD(list); @@ -950,7 +955,7 @@ static void defer_request(struct i915_re GEM_BUG_ON(i915_request_is_active(rq)); list_move_tail(&rq->sched.link, pl);
- list_for_each_entry(p, &rq->sched.waiters_list, wait_link) { + for_each_waiter(p, rq) { struct i915_request *w = container_of(p->waiter, typeof(*w), sched);
--- a/drivers/gpu/drm/i915/i915_scheduler.c +++ b/drivers/gpu/drm/i915/i915_scheduler.c @@ -418,8 +418,6 @@ bool __i915_sched_node_add_dependency(st
if (!node_signaled(signal)) { INIT_LIST_HEAD(&dep->dfs_link); - list_add(&dep->wait_link, &signal->waiters_list); - list_add(&dep->signal_link, &node->signalers_list); dep->signaler = signal; dep->waiter = node; dep->flags = flags; @@ -429,6 +427,10 @@ bool __i915_sched_node_add_dependency(st !node_started(signal)) node->flags |= I915_SCHED_HAS_SEMAPHORE_CHAIN;
+ /* All set, now publish. Beware the lockless walkers. */ + list_add(&dep->signal_link, &node->signalers_list); + list_add_rcu(&dep->wait_link, &signal->waiters_list); + /* * As we do not allow WAIT to preempt inflight requests, * once we have executed a request, along with triggering