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

[Yuanzheng Song]

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