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Date: Mon, 25 Oct 2021 07:00:15 +0000
From: Yuanzheng Song <songyuanzheng@...wei.com>
To: <dennis@...nel.org>, <tj@...nel.org>, <cl@...ux.com>,
<akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
<linux-kernel@...r.kernel.org>
Subject: [PATCH -next] mm/percpu: fix data-race with pcpu_nr_empty_pop_pages
When reading the pcpu_nr_empty_pop_pages in pcpu_alloc()
and writing the pcpu_nr_empty_pop_pages in
pcpu_update_empty_pages() at the same time,
the data-race occurs.
===========
read-write to 0xffffffff882fdd4c of 4 bytes by task 9424 on cpu 0:
pcpu_update_empty_pages
pcpu_chunk_populated
pcpu_balance_populated
pcpu_balance_workfn
process_one_work
worker_thread
kthread
ret_from_fork
read to 0xffffffff882fdd4c of 4 bytes by task 9386 on cpu 3:
pcpu_alloc
__alloc_percpu_gfp
fib_nh_common_init
fib_nh_init
fib_create_info
fib_table_insert
fib_magic
......
sock_sendmsg_nosec
sock_sendmsg
__sys_sendto
__do_sys_sendto
__se_sys_sendto
__x64_sys_sendto
do_syscall_64
entry_SYSCALL_64_after_hwframe
============
The same problem will occur in these functions:
pcpu_reclaim_populated(), pcpu_update_empty_pages(),
pcpu_isolate_chunk().
To fix this issue, use READ_ONCE() and WRITE_ONCE() to
read and write the pcpu_nr_empty_pop_pages.
Signed-off-by: Yuanzheng Song <songyuanzheng@...wei.com>
---
mm/percpu.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/mm/percpu.c b/mm/percpu.c
index 293009cc03ef..e8ef92e698ab 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -574,7 +574,9 @@ static void pcpu_isolate_chunk(struct pcpu_chunk *chunk)
if (!chunk->isolated) {
chunk->isolated = true;
- pcpu_nr_empty_pop_pages -= chunk->nr_empty_pop_pages;
+ WRITE_ONCE(pcpu_nr_empty_pop_pages,
+ READ_ONCE(pcpu_nr_empty_pop_pages) -
+ chunk->nr_empty_pop_pages);
}
list_move(&chunk->list, &pcpu_chunk_lists[pcpu_to_depopulate_slot]);
}
@@ -585,7 +587,9 @@ static void pcpu_reintegrate_chunk(struct pcpu_chunk *chunk)
if (chunk->isolated) {
chunk->isolated = false;
- pcpu_nr_empty_pop_pages += chunk->nr_empty_pop_pages;
+ WRITE_ONCE(pcpu_nr_empty_pop_pages,
+ READ_ONCE(pcpu_nr_empty_pop_pages) +
+ chunk->nr_empty_pop_pages);
pcpu_chunk_relocate(chunk, -1);
}
}
@@ -603,7 +607,8 @@ static inline void pcpu_update_empty_pages(struct pcpu_chunk *chunk, int nr)
{
chunk->nr_empty_pop_pages += nr;
if (chunk != pcpu_reserved_chunk && !chunk->isolated)
- pcpu_nr_empty_pop_pages += nr;
+ WRITE_ONCE(pcpu_nr_empty_pop_pages,
+ READ_ONCE(pcpu_nr_empty_pop_pages) + nr);
}
/*
@@ -1874,7 +1879,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
mutex_unlock(&pcpu_alloc_mutex);
}
- if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)
+ if (READ_ONCE(pcpu_nr_empty_pop_pages) < PCPU_EMPTY_POP_PAGES_LOW)
pcpu_schedule_balance_work();
/* clear the areas and return address relative to base address */
@@ -2062,7 +2067,7 @@ static void pcpu_balance_populated(void)
pcpu_atomic_alloc_failed = false;
} else {
nr_to_pop = clamp(PCPU_EMPTY_POP_PAGES_HIGH -
- pcpu_nr_empty_pop_pages,
+ READ_ONCE(pcpu_nr_empty_pop_pages),
0, PCPU_EMPTY_POP_PAGES_HIGH);
}
@@ -2163,7 +2168,8 @@ static void pcpu_reclaim_populated(void)
break;
/* reintegrate chunk to prevent atomic alloc failures */
- if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_HIGH) {
+ if (READ_ONCE(pcpu_nr_empty_pop_pages) <
+ PCPU_EMPTY_POP_PAGES_HIGH) {
reintegrate = true;
goto end_chunk;
}
--
2.25.1
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