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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Yongji Xie <elohimes@gmail.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Waiman Long <longman@redhat.com>,
	Will Deacon <will.deacon@arm.com>, Ingo Molnar <mingo@kernel.org>,
	Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Subject: [PATCH 4.14 51/62] sched/wake_q: Fix wakeup ordering for wake_q
Date: Fri,  8 Nov 2019 19:50:39 +0100
Message-ID: <20191108174754.515925895@linuxfoundation.org> (raw)
In-Reply-To: <20191108174719.228826381@linuxfoundation.org>

From: Peter Zijlstra <peterz@infradead.org>

commit 4c4e3731564c8945ac5ac90fc2a1e1f21cb79c92 upstream.

Notable cmpxchg() does not provide ordering when it fails, however
wake_q_add() requires ordering in this specific case too. Without this
it would be possible for the concurrent wakeup to not observe our
prior state.

Andrea Parri provided:

  C wake_up_q-wake_q_add

  {
	int next = 0;
	int y = 0;
  }

  P0(int *next, int *y)
  {
	int r0;

	/* in wake_up_q() */

	WRITE_ONCE(*next, 1);   /* node->next = NULL */
	smp_mb();               /* implied by wake_up_process() */
	r0 = READ_ONCE(*y);
  }

  P1(int *next, int *y)
  {
	int r1;

	/* in wake_q_add() */

	WRITE_ONCE(*y, 1);      /* wake_cond = true */
	smp_mb__before_atomic();
	r1 = cmpxchg_relaxed(next, 1, 2);
  }

  exists (0:r0=0 /\ 1:r1=0)

  This "exists" clause cannot be satisfied according to the LKMM:

  Test wake_up_q-wake_q_add Allowed
  States 3
  0:r0=0; 1:r1=1;
  0:r0=1; 1:r1=0;
  0:r0=1; 1:r1=1;
  No
  Witnesses
  Positive: 0 Negative: 3
  Condition exists (0:r0=0 /\ 1:r1=0)
  Observation wake_up_q-wake_q_add Never 0 3

Reported-by: Yongji Xie <elohimes@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/sched/core.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -432,10 +432,11 @@ void wake_q_add(struct wake_q_head *head
 	 * its already queued (either by us or someone else) and will get the
 	 * wakeup due to that.
 	 *
-	 * This cmpxchg() implies a full barrier, which pairs with the write
-	 * barrier implied by the wakeup in wake_up_q().
+	 * In order to ensure that a pending wakeup will observe our pending
+	 * state, even in the failed case, an explicit smp_mb() must be used.
 	 */
-	if (cmpxchg(&node->next, NULL, WAKE_Q_TAIL))
+	smp_mb__before_atomic();
+	if (cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL))
 		return;
 
 	get_task_struct(task);



  parent reply index

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-08 18:49 [PATCH 4.14 00/62] 4.14.153-stable review Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 01/62] arm64: dts: Fix gpio to pinmux mapping Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 02/62] regulator: ti-abb: Fix timeout in ti_abb_wait_txdone/ti_abb_clear_all_txdone Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 03/62] regulator: pfuze100-regulator: Variable "val" in pfuze100_regulator_probe() could be uninitialized Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 04/62] ASoC: wm_adsp: Dont generate kcontrols without READ flags Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 05/62] ASoc: rockchip: i2s: Fix RPM imbalance Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 06/62] ARM: dts: logicpd-torpedo-som: Remove twl_keypad Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 07/62] pinctrl: ns2: Fix off by one bugs in ns2_pinmux_enable() Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 08/62] ARM: mm: fix alignment handler faults under memory pressure Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 09/62] scsi: scsi_dh_alua: handle RTPG sense code correctly during state transitions Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 10/62] scsi: sni_53c710: fix compilation error Greg Kroah-Hartman
2019-11-08 18:49 ` [PATCH 4.14 11/62] scsi: fix kconfig dependency warning related to 53C700_LE_ON_BE Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 12/62] ARM: dts: imx7s: Correct GPTs ipg clock source Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 13/62] perf c2c: Fix memory leak in build_cl_output() Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 14/62] perf kmem: Fix memory leak in compact_gfp_flags() Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 15/62] ARM: davinci: dm365: Fix McBSP dma_slave_map entry Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 16/62] scsi: target: core: Do not overwrite CDB byte 1 Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 17/62] ARM: 8926/1: v7m: remove register save to stack before svc Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 18/62] of: unittest: fix memory leak in unittest_data_add Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 19/62] MIPS: bmips: mark exception vectors as char arrays Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 20/62] i2c: stm32f7: remove warning when compiling with W=1 Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 21/62] cifs: Fix cifsInodeInfo lock_sem deadlock when reconnect occurs Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 22/62] nbd: handle racing with errored out commands Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 23/62] cxgb4: fix panic when attaching to ULD fail Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 24/62] dccp: do not leak jiffies on the wire Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 25/62] net: annotate accesses to sk->sk_incoming_cpu Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 26/62] net: annotate lockless accesses to sk->sk_napi_id Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 27/62] net: dsa: bcm_sf2: Fix IMP setup for port different than 8 Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 28/62] net: ethernet: ftgmac100: Fix DMA coherency issue with SW checksum Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 29/62] net: fix sk_page_frag() recursion from memory reclaim Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 30/62] net: hisilicon: Fix ping latency when deal with high throughput Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 31/62] net/mlx4_core: Dynamically set guaranteed amount of counters per VF Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 32/62] net: Zeroing the structure ethtool_wolinfo in ethtool_get_wol() Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 33/62] selftests: net: reuseport_dualstack: fix uninitalized parameter Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 34/62] udp: fix data-race in udp_set_dev_scratch() Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 35/62] net: add READ_ONCE() annotation in __skb_wait_for_more_packets() Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 36/62] net/mlx5e: Fix handling of compressed CQEs in case of low NAPI budget Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 37/62] net: dsa: b53: Do not clear existing mirrored port mask Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 38/62] net: usb: lan78xx: Connect PHY before registering MAC Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 39/62] r8152: add device id for Lenovo ThinkPad USB-C Dock Gen 2 Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 40/62] net: dsa: fix switch tree list Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 41/62] net: bcmgenet: reset 40nm EPHY on energy detect Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 42/62] net: add skb_queue_empty_lockless() Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 43/62] udp: use skb_queue_empty_lockless() Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 44/62] net: use skb_queue_empty_lockless() in poll() handlers Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 45/62] net: use skb_queue_empty_lockless() in busy poll contexts Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 46/62] vxlan: check tun_info options_len properly Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 47/62] erspan: fix the tun_info options_len check for erspan Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 48/62] inet: stop leaking jiffies on the wire Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 49/62] net/flow_dissector: switch to siphash Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 50/62] dmaengine: qcom: bam_dma: Fix resource leak Greg Kroah-Hartman
2019-11-08 18:50 ` Greg Kroah-Hartman [this message]
2019-11-08 18:50 ` [PATCH 4.14 52/62] kbuild: use -fmacro-prefix-map to make __FILE__ a relative path Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 53/62] kbuild: add -fcf-protection=none when using retpoline flags Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 54/62] platform/x86: pmc_atom: Add Siemens SIMATIC IPC227E to critclk_systems DMI table Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 55/62] iio: adc: stm32-adc: move registers definitions Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 56/62] iio: adc: stm32-adc: fix a race when using several adcs with dma and irq Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 57/62] powerpc/mm: Fixup tlbie vs store ordering issue on POWER9 Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 58/62] powerpc/book3s64/mm: Dont do tlbie fixup for some hardware revisions Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 59/62] powerpc/book3s64/radix: Rename CPU_FTR_P9_TLBIE_BUG feature flag Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 60/62] powerpc/mm: Fixup tlbie vs mtpidr/mtlpidr ordering issue on POWER9 Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 61/62] selftests/powerpc: Add test case for tlbie vs mtpidr ordering issue Greg Kroah-Hartman
2019-11-08 18:50 ` [PATCH 4.14 62/62] selftests/powerpc: Fix compile error on tlbie_test due to newer gcc Greg Kroah-Hartman
2019-11-09  1:57 ` [PATCH 4.14 00/62] 4.14.153-stable review kernelci.org bot
2019-11-09 10:19 ` Naresh Kamboju
2019-11-09 15:40 ` Guenter Roeck

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