[PATCH -next] mm/vmpressure: fix data-race with memcg->socket_pressure

From: Yuanzheng Song
Date: Mon Oct 25 2021 - 04:14:45 EST


BUG: KCSAN: data-race in __sk_mem_reduce_allocated / vmpressure

write to 0xffff8881286f4938 of 8 bytes by task 24550 on cpu 3:
vmpressure+0x218/0x230 mm/vmpressure.c:307
shrink_node_memcgs+0x2b9/0x410 mm/vmscan.c:2658
shrink_node+0x9d2/0x11d0 mm/vmscan.c:2769
shrink_zones+0x29f/0x470 mm/vmscan.c:2972
do_try_to_free_pages+0x193/0x6e0 mm/vmscan.c:3027
try_to_free_mem_cgroup_pages+0x1c0/0x3f0 mm/vmscan.c:3345
reclaim_high mm/memcontrol.c:2440 [inline]
mem_cgroup_handle_over_high+0x18b/0x4d0 mm/memcontrol.c:2624
tracehook_notify_resume include/linux/tracehook.h:197 [inline]
exit_to_user_mode_loop kernel/entry/common.c:164 [inline]
exit_to_user_mode_prepare+0x110/0x170 kernel/entry/common.c:191
syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:266
ret_from_fork+0x15/0x30 arch/x86/entry/entry_64.S:289

read to 0xffff8881286f4938 of 8 bytes by interrupt on cpu 1:
mem_cgroup_under_socket_pressure include/linux/memcontrol.h:1483 [inline]
sk_under_memory_pressure include/net/sock.h:1314 [inline]
__sk_mem_reduce_allocated+0x1d2/0x270 net/core/sock.c:2696
__sk_mem_reclaim+0x44/0x50 net/core/sock.c:2711
sk_mem_reclaim include/net/sock.h:1490 [inline]
......
net_rx_action+0x17a/0x480 net/core/dev.c:6864
__do_softirq+0x12c/0x2af kernel/softirq.c:298
run_ksoftirqd+0x13/0x20 kernel/softirq.c:653
smpboot_thread_fn+0x33f/0x510 kernel/smpboot.c:165
kthread+0x1fc/0x220 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

When reading memcg->socket_pressure in mem_cgroup_under_socket_pressure()
and writing memcg->socket_pressure in vmpressure() at the same time,
the data-race occurs.

So fix it by using READ_ONCE() and WRITE_ONCE() to read and write
memcg->socket_pressure.

Signed-off-by: Yuanzheng Song <songyuanzheng@xxxxxxxxxx>
---
include/linux/memcontrol.h | 2 +-
mm/vmpressure.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e34bf0cbdf55..d06bbac14abc 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1667,7 +1667,7 @@ static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && memcg->tcpmem_pressure)
return true;
do {
- if (time_before(jiffies, memcg->socket_pressure))
+ if (time_before(jiffies, READ_ONCE(memcg->socket_pressure)))
return true;
} while ((memcg = parent_mem_cgroup(memcg)));
return false;
diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index 76518e4166dc..b52644771cc4 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -308,7 +308,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
* asserted for a second in which subsequent
* pressure events can occur.
*/
- memcg->socket_pressure = jiffies + HZ;
+ WRITE_ONCE(memcg->socket_pressure, jiffies + HZ);
}
}
}
--
2.25.1