+ mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch added to -mm tree

+ mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm/vmstat: protect per cpu variables with preempt disable on RT
has been added to the -mm tree.  Its filename is
     mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch

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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Ingo Molnar <mingo@elte.hu>
Subject: mm/vmstat: protect per cpu variables with preempt disable on RT

Disable preemption on -RT for the vmstat code.  On vanilla the code runs
in IRQ-off regions while on -RT it may not when stats are updated under a
local_lock.  "preempt_disable" ensures that the same resources are not
updated in parallel due to preemption.

This patch differs from the preempt-rt version where __count_vm_event and
__count_vm_events are also protected.  The counters are explicitly
"allowed to be to be racy" so there is no need to protect them from
preemption.  Only the accurate page stats that are updated by a
read-modify-write need protection.

Link: https://lkml.kernel.org/r/20210723100034.13353-3-mgorman@techsingularity.net
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vmstat.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/mm/vmstat.c~mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt
+++ a/mm/vmstat.c
@@ -319,6 +319,7 @@ void __mod_zone_page_state(struct zone *
 	long x;
 	long t;
 
+	preempt_disable_rt();
 	x = delta + __this_cpu_read(*p);
 
 	t = __this_cpu_read(pcp->stat_threshold);
@@ -328,6 +329,7 @@ void __mod_zone_page_state(struct zone *
 		x = 0;
 	}
 	__this_cpu_write(*p, x);
+	preempt_enable_rt();
 }
 EXPORT_SYMBOL(__mod_zone_page_state);
 
@@ -350,6 +352,7 @@ void __mod_node_page_state(struct pglist
 		delta >>= PAGE_SHIFT;
 	}
 
+	preempt_disable_rt();
 	x = delta + __this_cpu_read(*p);
 
 	t = __this_cpu_read(pcp->stat_threshold);
@@ -359,6 +362,7 @@ void __mod_node_page_state(struct pglist
 		x = 0;
 	}
 	__this_cpu_write(*p, x);
+	preempt_enable_rt();
 }
 EXPORT_SYMBOL(__mod_node_page_state);
 
@@ -391,6 +395,7 @@ void __inc_zone_state(struct zone *zone,
 	s8 __percpu *p = pcp->vm_stat_diff + item;
 	s8 v, t;
 
+	preempt_disable_rt();
 	v = __this_cpu_inc_return(*p);
 	t = __this_cpu_read(pcp->stat_threshold);
 	if (unlikely(v > t)) {
@@ -399,6 +404,7 @@ void __inc_zone_state(struct zone *zone,
 		zone_page_state_add(v + overstep, zone, item);
 		__this_cpu_write(*p, -overstep);
 	}
+	preempt_enable_rt();
 }
 
 void __inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
@@ -409,6 +415,7 @@ void __inc_node_state(struct pglist_data
 
 	VM_WARN_ON_ONCE(vmstat_item_in_bytes(item));
 
+	preempt_disable_rt();
 	v = __this_cpu_inc_return(*p);
 	t = __this_cpu_read(pcp->stat_threshold);
 	if (unlikely(v > t)) {
@@ -417,6 +424,7 @@ void __inc_node_state(struct pglist_data
 		node_page_state_add(v + overstep, pgdat, item);
 		__this_cpu_write(*p, -overstep);
 	}
+	preempt_enable_rt();
 }
 
 void __inc_zone_page_state(struct page *page, enum zone_stat_item item)
@@ -437,6 +445,7 @@ void __dec_zone_state(struct zone *zone,
 	s8 __percpu *p = pcp->vm_stat_diff + item;
 	s8 v, t;
 
+	preempt_disable_rt();
 	v = __this_cpu_dec_return(*p);
 	t = __this_cpu_read(pcp->stat_threshold);
 	if (unlikely(v < - t)) {
@@ -445,6 +454,7 @@ void __dec_zone_state(struct zone *zone,
 		zone_page_state_add(v - overstep, zone, item);
 		__this_cpu_write(*p, overstep);
 	}
+	preempt_enable_rt();
 }
 
 void __dec_node_state(struct pglist_data *pgdat, enum node_stat_item item)
@@ -455,6 +465,7 @@ void __dec_node_state(struct pglist_data
 
 	VM_WARN_ON_ONCE(vmstat_item_in_bytes(item));
 
+	preempt_disable_rt();
 	v = __this_cpu_dec_return(*p);
 	t = __this_cpu_read(pcp->stat_threshold);
 	if (unlikely(v < - t)) {
@@ -463,6 +474,7 @@ void __dec_node_state(struct pglist_data
 		node_page_state_add(v - overstep, pgdat, item);
 		__this_cpu_write(*p, overstep);
 	}
+	preempt_enable_rt();
 }
 
 void __dec_zone_page_state(struct page *page, enum zone_stat_item item)
_

Patches currently in -mm which might be from mingo@elte.hu are

mm-vmstat-protect-per-cpu-variables-with-preempt-disable-on-rt.patch