linux-kernel - [PATCH v2] x86/platform/uv/BAU: disable BAU on single hub configurations

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Message-Id: <1500588351-78016-1-git-send-email-abanman@hpe.com>
Date:   Thu, 20 Jul 2017 17:05:51 -0500
From:   Andrew Banman <abanman@....com>
To:     mingo@...hat.com
Cc:     Andrew Banman <abanman@....com>, tglx@...utronix.de,
        x86@...nel.org, linux-kernel@...r.kernel.org, rja@....com,
        mike.travis@....com, tony.ernst@....com
Subject: [PATCH v2] x86/platform/uv/BAU: disable BAU on single hub configurations

The BAU confers no benefit to a UV system running with only one hub/socket.
Permanently disable the BAU driver if there are less than two hubs online
to avoid BAU overhead. We have observed failed boots on single-socket UV4
systems caused by BAU that are avoided with this patch.

Version 2: Consolidate initialization error blocks with goto err_bau_disable
and free the per_cpu cpumasks to fix a memory leak.

Signed-off-by: Andrew Banman <abanman@....com>
Acked-by: Russ Anderson <rja@....com>
Acked-by: Mike Travis <mike.travis@....com>
---
 arch/x86/platform/uv/tlb_uv.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
index 2511a28..e4a51a6 100644
--- a/arch/x86/platform/uv/tlb_uv.c
+++ b/arch/x86/platform/uv/tlb_uv.c
@@ -2245,13 +2245,17 @@ static int __init uv_bau_init(void)
 	else if (is_uv1_hub())
 		ops = uv1_bau_ops;
 
+	nuvhubs = uv_num_possible_blades();
+	if (nuvhubs < 2) {
+		pr_crit("UV: BAU disabled - insufficient hub count\n");
+		goto err_bau_disable;
+	}
+
 	for_each_possible_cpu(cur_cpu) {
 		mask = &per_cpu(uv_flush_tlb_mask, cur_cpu);
 		zalloc_cpumask_var_node(mask, GFP_KERNEL, cpu_to_node(cur_cpu));
 	}
 
-	nuvhubs = uv_num_possible_blades();
-
 	uv_base_pnode = 0x7fffffff;
 	for (uvhub = 0; uvhub < nuvhubs; uvhub++) {
 		cpus = uv_blade_nr_possible_cpus(uvhub);
@@ -2264,9 +2268,8 @@ static int __init uv_bau_init(void)
 		enable_timeouts();
 
 	if (init_per_cpu(nuvhubs, uv_base_pnode)) {
-		set_bau_off();
-		nobau_perm = 1;
-		return 0;
+		pr_crit("UV: BAU disabled - per CPU init failed\n");
+		goto err_bau_disable;
 	}
 
 	vector = UV_BAU_MESSAGE;
@@ -2292,6 +2295,14 @@ static int __init uv_bau_init(void)
 	}
 
 	return 0;
+
+err_bau_disable:
+	for_each_possible_cpu(cur_cpu) {
+		free_cpumask_var(per_cpu(uv_flush_tlb_mask, cur_cpu));
+	}
+	set_bau_off();
+	nobau_perm = 1;
+	return -EINVAL;
 }
 core_initcall(uv_bau_init);
 fs_initcall(uv_ptc_init);
-- 
1.8.2.1