linux-kernel - [PATCH 4.15 062/168] staging: lustre: disable preempt while sampling processor id.

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Message-Id: <20180410212802.839699613@linuxfoundation.org>
Date:   Wed, 11 Apr 2018 00:23:24 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, NeilBrown <neilb@...e.com>,
        Andreas Dilger <andreas.dilger@...el.com>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.15 062/168] staging: lustre: disable preempt while sampling processor id.

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: NeilBrown <neilb@...e.com>


[ Upstream commit dbeccabf5294e80f7cc9ee566746c42211bed736 ]

Calling smp_processor_id() without disabling preemption
triggers a warning (if CONFIG_DEBUG_PREEMPT).
I think the result of cfs_cpt_current() is only used as a hint for
load balancing, rather than as a precise and stable indicator of
the current CPU.  So it doesn't need to be called with
preemption disabled.

So disable preemption inside cfs_cpt_current() to silence the warning.

Signed-off-by: NeilBrown <neilb@...e.com>
Reviewed-by: Andreas Dilger <andreas.dilger@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/staging/lustre/lnet/libcfs/linux/linux-cpu.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

--- a/drivers/staging/lustre/lnet/libcfs/linux/linux-cpu.c
+++ b/drivers/staging/lustre/lnet/libcfs/linux/linux-cpu.c
@@ -529,19 +529,20 @@ EXPORT_SYMBOL(cfs_cpt_spread_node);
 int
 cfs_cpt_current(struct cfs_cpt_table *cptab, int remap)
 {
-	int cpu = smp_processor_id();
-	int cpt = cptab->ctb_cpu2cpt[cpu];
+	int cpu;
+	int cpt;
 
-	if (cpt < 0) {
-		if (!remap)
-			return cpt;
+	preempt_disable();
+	cpu = smp_processor_id();
+	cpt = cptab->ctb_cpu2cpt[cpu];
 
+	if (cpt < 0 && remap) {
 		/* don't return negative value for safety of upper layer,
 		 * instead we shadow the unknown cpu to a valid partition ID
 		 */
 		cpt = cpu % cptab->ctb_nparts;
 	}
-
+	preempt_enable();
 	return cpt;
 }
 EXPORT_SYMBOL(cfs_cpt_current);