From 08813496570879fbcc2adcdd9ddc0a054361bfde Mon Sep 17 00:00:00 2001 From: Olivier Houchard Date: Mon, 6 Aug 2018 21:58:42 +0200 Subject: [PATCH] spinlock/hclh: Strictly follow the algorithm instead of taking shortcuts. Don't attempt to be to smart, and just follow the algorithm, failing to do so may lead to getting a thread to wrongly believe it owns the lock when it does not. This should fix the random failures reported on PPC with many threads. --- include/spinlock/hclh.h | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/include/spinlock/hclh.h b/include/spinlock/hclh.h index 296448b..ece56c6 100644 --- a/include/spinlock/hclh.h +++ b/include/spinlock/hclh.h @@ -81,6 +81,8 @@ ck_spinlock_hclh_lock(struct ck_spinlock_hclh **glob_queue, thread->wait = true; thread->splice = false; thread->cluster_id = (*local_queue)->cluster_id; + /* Make sure previous->previous doesn't appear to be NULL */ + thread->previous = *local_queue; /* Serialize with respect to update of local queue. */ ck_pr_fence_store_atomic(); @@ -91,13 +93,15 @@ ck_spinlock_hclh_lock(struct ck_spinlock_hclh **glob_queue, /* Wait until previous thread from the local queue is done with lock. */ ck_pr_fence_load(); - if (previous->previous != NULL && - previous->cluster_id == thread->cluster_id) { - while (ck_pr_load_uint(&previous->wait) == true) + if (previous->previous != NULL) { + while (ck_pr_load_uint(&previous->wait) == true && + ck_pr_load_int(&previous->cluster_id) == thread->cluster_id && + ck_pr_load_uint(&previous->splice) == false) ck_pr_stall(); /* We're head of the global queue, we're done */ - if (ck_pr_load_uint(&previous->splice) == false) + if (ck_pr_load_int(&previous->cluster_id) == thread->cluster_id && + ck_pr_load_uint(&previous->splice) == false) return; }