Patch "staging: lustre: disable preempt while sampling processor id." has been added to the 4.15-stable tree

Patch "staging: lustre: disable preempt while sampling processor id." has been added to the 4.15-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    staging: lustre: disable preempt while sampling processor id.

to the 4.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     staging-lustre-disable-preempt-while-sampling-processor-id.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Mon Apr  9 10:16:32 CEST 2018
From: NeilBrown <neilb@suse.com>
Date: Tue, 19 Dec 2017 10:01:47 +1100
Subject: staging: lustre: disable preempt while sampling processor id.

From: NeilBrown <neilb@suse.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@suse.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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);


Patches currently in stable-queue which might be from neilb@suse.com are

queue-4.15/staging-lustre-disable-preempt-while-sampling-processor-id.patch
queue-4.15/vfs-close-race-between-getcwd-and-d_move.patch