The patch titled
Subject: percpu: fix data race with pcpu_nr_empty_pop_pages
has been added to the -mm mm-unstable branch. Its filename is
percpu-fix-data-race-with-pcpu_nr_empty_pop_pages.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/percpu-fix-data-race-with-pcpu_nr_empty_pop_pages.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Dennis Zhou <dennis@xxxxxxxxxx>
Subject: percpu: fix data race with pcpu_nr_empty_pop_pages
Date: Mon, 7 Oct 2024 17:19:42 -0700
Fixes the data race by moving the read to be behind the pcpu_lock. This
is okay because the code (initially) above it will not increase the
empty populated page count because it is populating backing pages that
already have allocations served out of them.
Link: https://lkml.kernel.org/r/20241008001942.8114-1-dennis@xxxxxxxxxx
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202407191651.f24e499d-oliver.sang@xxxxxxxxx
Signed-off-by: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/percpu.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
--- a/mm/percpu.c~percpu-fix-data-race-with-pcpu_nr_empty_pop_pages
+++ a/mm/percpu.c
@@ -1864,6 +1864,10 @@ restart:
area_found:
pcpu_stats_area_alloc(chunk, size);
+
+ if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)
+ pcpu_schedule_balance_work();
+
spin_unlock_irqrestore(&pcpu_lock, flags);
/* populate if not all pages are already there */
@@ -1891,9 +1895,6 @@ area_found:
mutex_unlock(&pcpu_alloc_mutex);
}
- if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)
- pcpu_schedule_balance_work();
-
/* clear the areas and return address relative to base address */
for_each_possible_cpu(cpu)
memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);
_
Patches currently in -mm which might be from dennis@xxxxxxxxxx are
percpu-fix-data-race-with-pcpu_nr_empty_pop_pages.patch
