[PATCH 4.19 089/114] hrtimer: Annotate lockless access to timer->state

Greg Kroah-Hartman
2020-01-02T22:53:10Z

From: Eric Dumazet <edumazet@google.com>

commit 56144737e67329c9aaed15f942d46a6302e2e3d8 upstream.

syzbot reported various data-race caused by hrtimer_is_queued() reading
timer->state. A READ_ONCE() is required there to silence the warning.

Also add the corresponding WRITE_ONCE() when timer->state is set.

In remove_hrtimer() the hrtimer_is_queued() helper is open coded to avoid
loading timer->state twice.

KCSAN reported these cases:

BUG: KCSAN: data-race in __remove_hrtimer / tcp_pacing_check

write to 0xffff8880b2a7d388 of 1 bytes by interrupt on cpu 0:
__remove_hrtimer+0x52/0x130 kernel/time/hrtimer.c:991
__run_hrtimer kernel/time/hrtimer.c:1496 [inline]
__hrtimer_run_queues+0x250/0x600 kernel/time/hrtimer.c:1576
hrtimer_run_softirq+0x10e/0x150 kernel/time/hrtimer.c:1593
__do_softirq+0x115/0x33f kernel/softirq.c:292
run_ksoftirqd+0x46/0x60 kernel/softirq.c:603
smpboot_thread_fn+0x37d/0x4a0 kernel/smpboot.c:165
kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff8880b2a7d388 of 1 bytes by task 24652 on cpu 1:
tcp_pacing_check net/ipv4/tcp_output.c:2235 [inline]
tcp_pacing_check+0xba/0x130 net/ipv4/tcp_output.c:2225
tcp_xmit_retransmit_queue+0x32c/0x5a0 net/ipv4/tcp_output.c:3044
tcp_xmit_recovery+0x7c/0x120 net/ipv4/tcp_input.c:3558
tcp_ack+0x17b6/0x3170 net/ipv4/tcp_input.c:3717
tcp_rcv_established+0x37e/0xf50 net/ipv4/tcp_input.c:5696
tcp_v4_do_rcv+0x381/0x4e0 net/ipv4/tcp_ipv4.c:1561
sk_backlog_rcv include/net/sock.h:945 [inline]
__release_sock+0x135/0x1e0 net/core/sock.c:2435
release_sock+0x61/0x160 net/core/sock.c:2951
sk_stream_wait_memory+0x3d7/0x7c0 net/core/stream.c:145
tcp_sendmsg_locked+0xb47/0x1f30 net/ipv4/tcp.c:1393
tcp_sendmsg+0x39/0x60 net/ipv4/tcp.c:1434
inet_sendmsg+0x6d/0x90 net/ipv4/af_inet.c:807
sock_sendmsg_nosec net/socket.c:637 [inline]
sock_sendmsg+0x9f/0xc0 net/socket.c:657

BUG: KCSAN: data-race in __remove_hrtimer / __tcp_ack_snd_check

write to 0xffff8880a3a65588 of 1 bytes by interrupt on cpu 0:
__remove_hrtimer+0x52/0x130 kernel/time/hrtimer.c:991
__run_hrtimer kernel/time/hrtimer.c:1496 [inline]
__hrtimer_run_queues+0x250/0x600 kernel/time/hrtimer.c:1576
hrtimer_run_softirq+0x10e/0x150 kernel/time/hrtimer.c:1593
__do_softirq+0x115/0x33f kernel/softirq.c:292
invoke_softirq kernel/softirq.c:373 [inline]
irq_exit+0xbb/0xe0 kernel/softirq.c:413
exiting_irq arch/x86/include/asm/apic.h:536 [inline]
smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830

read to 0xffff8880a3a65588 of 1 bytes by task 22891 on cpu 1:
__tcp_ack_snd_check+0x415/0x4f0 net/ipv4/tcp_input.c:5265
tcp_ack_snd_check net/ipv4/tcp_input.c:5287 [inline]
tcp_rcv_established+0x750/0xf50 net/ipv4/tcp_input.c:5708
tcp_v4_do_rcv+0x381/0x4e0 net/ipv4/tcp_ipv4.c:1561
sk_backlog_rcv include/net/sock.h:945 [inline]
__release_sock+0x135/0x1e0 net/core/sock.c:2435
release_sock+0x61/0x160 net/core/sock.c:2951
sk_stream_wait_memory+0x3d7/0x7c0 net/core/stream.c:145
tcp_sendmsg_locked+0xb47/0x1f30 net/ipv4/tcp.c:1393
tcp_sendmsg+0x39/0x60 net/ipv4/tcp.c:1434
inet_sendmsg+0x6d/0x90 net/ipv4/af_inet.c:807
sock_sendmsg_nosec net/socket.c:637 [inline]
sock_sendmsg+0x9f/0xc0 net/socket.c:657
__sys_sendto+0x21f/0x320 net/socket.c:1952
__do_sys_sendto net/socket.c:1964 [inline]
__se_sys_sendto net/socket.c:1960 [inline]
__x64_sys_sendto+0x89/0xb0 net/socket.c:1960
do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 24652 Comm: syz-executor.3 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

[ tglx: Added comments ]

Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191106174804.74723-1-edumazet@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/hrtimer.h | 14 ++++++++++----
kernel/time/hrtimer.c | 11 +++++++----
2 files changed, 17 insertions(+), 8 deletions(-)

--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -430,12 +430,18 @@ extern u64 hrtimer_next_event_without(co

extern bool hrtimer_active(const struct hrtimer *timer);

-/*
- * Helper function to check, whether the timer is on one of the queues
+/**
+ * hrtimer_is_queued = check, whether the timer is on one of the queues
+ * @timer: Timer to check
+ *
+ * Returns: True if the timer is queued, false otherwise
+ *
+ * The function can be used lockless, but it gives only a current snapshot.
*/
-static inline int hrtimer_is_queued(struct hrtimer *timer)
+static inline bool hrtimer_is_queued(struct hrtimer *timer)
{
- return timer->state & HRTIMER_STATE_ENQUEUED;
+ /* The READ_ONCE pairs with the update functions of timer->state */
+ return !!(READ_ONCE(timer->state) & HRTIMER_STATE_ENQUEUED);
}

/*
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -955,7 +955,8 @@ static int enqueue_hrtimer(struct hrtime

base->cpu_base->active_bases |= 1 << base->index;

- timer->state = HRTIMER_STATE_ENQUEUED;
+ /* Pairs with the lockless read in hrtimer_is_queued() */
+ WRITE_ONCE(timer->state, HRTIMER_STATE_ENQUEUED);

return timerqueue_add(&base->active, &timer->node);
}
@@ -977,7 +978,8 @@ static void __remove_hrtimer(struct hrti
struct hrtimer_cpu_base *cpu_base = base->cpu_base;
u8 state = timer->state;

- timer->state = newstate;
+ /* Pairs with the lockless read in hrtimer_is_queued() */
+ WRITE_ONCE(timer->state, newstate);
if (!(state & HRTIMER_STATE_ENQUEUED))
return;

@@ -1002,8 +1004,9 @@ static void __remove_hrtimer(struct hrti
static inline int
remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base, bool restart)
{
- if (hrtimer_is_queued(timer)) {
- u8 state = timer->state;
+ u8 state = timer->state;
+
+ if (state & HRTIMER_STATE_ENQUEUED) {
int reprogram;

/*