diff mbox series

[179/262] mm/vmstat: annotate data race for zone->free_area[order].nr_free

Message ID 20211105204359.98NCTdblm%akpm@linux-foundation.org (mailing list archive)
State New
Headers show
Series [001/262] scripts/spelling.txt: add more spellings to spelling.txt | expand

Commit Message

Andrew Morton Nov. 5, 2021, 8:43 p.m. UTC 
From: Liu Shixin <liushixin2@huawei.com>
Subject: mm/vmstat: annotate data race for zone->free_area[order].nr_free

KCSAN reports a data-race on v5.10 which also exists on mainline:

==================================================================
BUG: KCSAN: data-race in extfrag_for_order+0x33/0x2d0

race at unknown origin, with read to 0xffff9ee9bfffab48 of 8 bytes by task 34 on cpu 1:
 extfrag_for_order+0x33/0x2d0
 kcompactd+0x5f0/0xce0
 kthread+0x1f9/0x220
 ret_from_fork+0x22/0x30

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 34 Comm: kcompactd0 Not tainted 5.10.0+ #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
==================================================================

Access to zone->free_area[order].nr_free in extfrag_for_order()/frag_show_print()
is lockless. That's intentional and the stats are a rough estimate anyway.
Annotate them with data_race().

[liushixin2@huawei.com: add comments]
  Link: https://lkml.kernel.org/r/20210918084655.2696522-1-liushixin2@huawei.com
Link: https://lkml.kernel.org/r/20210908015606.3999871-1-liushixin2@huawei.com
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vmstat.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)
diff mbox series

Patch

--- a/mm/vmstat.c~mm-vmstat-annotate-data-race-for-zone-free_areanr_free
+++ a/mm/vmstat.c
@@ -1070,8 +1070,13 @@  static void fill_contig_page_info(struct
 	for (order = 0; order < MAX_ORDER; order++) {
 		unsigned long blocks;
 
-		/* Count number of free blocks */
-		blocks = zone->free_area[order].nr_free;
+		/*
+		 * Count number of free blocks.
+		 *
+		 * Access to nr_free is lockless as nr_free is used only for
+		 * diagnostic purposes. Use data_race to avoid KCSAN warning.
+		 */
+		blocks = data_race(zone->free_area[order].nr_free);
 		info->free_blocks_total += blocks;
 
 		/* Count free base pages */
@@ -1446,7 +1451,11 @@  static void frag_show_print(struct seq_f
 
 	seq_printf(m, "Node %d, zone %8s ", pgdat->node_id, zone->name);
 	for (order = 0; order < MAX_ORDER; ++order)
-		seq_printf(m, "%6lu ", zone->free_area[order].nr_free);
+		/*
+		 * Access to nr_free is lockless as nr_free is used only for
+		 * printing purposes. Use data_race to avoid KCSAN warning.
+		 */
+		seq_printf(m, "%6lu ", data_race(zone->free_area[order].nr_free));
 	seq_putc(m, '\n');
 }