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From: Sasha Levin <Alexander.Levin@microsoft.com>
To: "stable@vger.kernel.org" <stable@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>,
	"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"akiyks@gmail.com" <akiyks@gmail.com>,
	"boqun.feng@gmail.com" <boqun.feng@gmail.com>,
	"dhowells@redhat.com" <dhowells@redhat.com>,
	"j.alglave@ucl.ac.uk" <j.alglave@ucl.ac.uk>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"luc.maranget@inria.fr" <luc.maranget@inria.fr>,
	"npiggin@gmail.com" <npiggin@gmail.com>,
	"parri.andrea@gmail.com" <parri.andrea@gmail.com>,
	"stern@rowland.harvard.edu" <stern@rowland.harvard.edu>,
	"will.deacon@arm.com" <will.deacon@arm.com>,
	Ingo Molnar <mingo@kernel.org>,
	Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL 4.14 17/57] sched/core: Use smp_mb() in wake_woken_function()
Date: Sat, 15 Sep 2018 01:32:40 +0000	[thread overview]
Message-ID: <20180915013223.179909-17-alexander.levin@microsoft.com> (raw)
In-Reply-To: <20180915013223.179909-1-alexander.levin@microsoft.com>

From: Andrea Parri <andrea.parri@amarulasolutions.com>

[ Upstream commit 76e079fefc8f62bd9b2cd2950814d1ee806e31a5 ]

wake_woken_function() synchronizes with wait_woken() as follows:

  [wait_woken]                       [wake_woken_function]

  entry->flags &= ~wq_flag_woken;    condition = true;
  smp_mb();                          smp_wmb();
  if (condition)                     wq_entry->flags |= wq_flag_woken;
     break;

This commit replaces the above smp_wmb() with an smp_mb() in order to
guarantee that either wait_woken() sees the wait condition being true
or the store to wq_entry->flags in woken_wake_function() follows the
store in wait_woken() in the coherence order (so that the former can
eventually be observed by wait_woken()).

The commit also fixes a comment associated to set_current_state() in
wait_woken(): the comment pairs the barrier in set_current_state() to
the above smp_wmb(), while the actual pairing involves the barrier in
set_current_state() and the barrier executed by the try_to_wake_up()
in wake_woken_function().

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akiyks@gmail.com
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: npiggin@gmail.com
Cc: parri.andrea@gmail.com
Cc: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/20180716180605.16115-10-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 kernel/sched/wait.c | 47 ++++++++++++++++++++-------------------------
 1 file changed, 21 insertions(+), 26 deletions(-)

diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 929ecb7d6b78..e29608464382 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -395,35 +395,36 @@ static inline bool is_kthread_should_stop(void)
  *     if (condition)
  *         break;
  *
- *     p->state = mode;				condition = true;
- *     smp_mb(); // A				smp_wmb(); // C
- *     if (!wq_entry->flags & WQ_FLAG_WOKEN)	wq_entry->flags |= WQ_FLAG_WOKEN;
- *         schedule()				try_to_wake_up();
- *     p->state = TASK_RUNNING;		    ~~~~~~~~~~~~~~~~~~
- *     wq_entry->flags &= ~WQ_FLAG_WOKEN;		condition = true;
- *     smp_mb() // B				smp_wmb(); // C
- *						wq_entry->flags |= WQ_FLAG_WOKEN;
- * }
- * remove_wait_queue(&wq_head, &wait);
+ *     // in wait_woken()			// in woken_wake_function()
  *
+ *     p->state = mode;				wq_entry->flags |= WQ_FLAG_WOKEN;
+ *     smp_mb(); // A				try_to_wake_up():
+ *     if (!(wq_entry->flags & WQ_FLAG_WOKEN))	   <full barrier>
+ *         schedule()				   if (p->state & mode)
+ *     p->state = TASK_RUNNING;			      p->state = TASK_RUNNING;
+ *     wq_entry->flags &= ~WQ_FLAG_WOKEN;	~~~~~~~~~~~~~~~~~~
+ *     smp_mb(); // B				condition = true;
+ * }						smp_mb(); // C
+ * remove_wait_queue(&wq_head, &wait);		wq_entry->flags |= WQ_FLAG_WOKEN;
  */
 long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
 {
-	set_current_state(mode); /* A */
 	/*
-	 * The above implies an smp_mb(), which matches with the smp_wmb() from
-	 * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
-	 * also observe all state before the wakeup.
+	 * The below executes an smp_mb(), which matches with the full barrier
+	 * executed by the try_to_wake_up() in woken_wake_function() such that
+	 * either we see the store to wq_entry->flags in woken_wake_function()
+	 * or woken_wake_function() sees our store to current->state.
 	 */
+	set_current_state(mode); /* A */
 	if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
 		timeout = schedule_timeout(timeout);
 	__set_current_state(TASK_RUNNING);
 
 	/*
-	 * The below implies an smp_mb(), it too pairs with the smp_wmb() from
-	 * woken_wake_function() such that we must either observe the wait
-	 * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
-	 * an event.
+	 * The below executes an smp_mb(), which matches with the smp_mb() (C)
+	 * in woken_wake_function() such that either we see the wait condition
+	 * being true or the store to wq_entry->flags in woken_wake_function()
+	 * follows ours in the coherence order.
 	 */
 	smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
 
@@ -433,14 +434,8 @@ EXPORT_SYMBOL(wait_woken);
 
 int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
 {
-	/*
-	 * Although this function is called under waitqueue lock, LOCK
-	 * doesn't imply write barrier and the users expects write
-	 * barrier semantics on wakeup functions.  The following
-	 * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
-	 * and is paired with smp_store_mb() in wait_woken().
-	 */
-	smp_wmb(); /* C */
+	/* Pairs with the smp_store_mb() in wait_woken(). */
+	smp_mb(); /* C */
 	wq_entry->flags |= WQ_FLAG_WOKEN;
 
 	return default_wake_function(wq_entry, mode, sync, key);
-- 
2.17.1

  parent reply	other threads:[~2018-09-15  1:43 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-15  1:32 [PATCH AUTOSEL 4.14 01/57] binfmt_elf: Respect error return from `regset->active' Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 02/57] net/mlx5: Add missing SET_DRIVER_VERSION command translation Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 03/57] arm64: dts: uniphier: Add missing cooling device properties for CPUs Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 04/57] audit: fix use-after-free in audit_add_watch Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 05/57] mtdchar: fix overflows in adjustment of `count` Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 07/57] Bluetooth: Use lock_sock_nested in bt_accept_enqueue Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 06/57] vfs: fix freeze protection in mnt_want_write_file() for overlayfs Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 08/57] mtd: rawnand: sunxi: Add an U suffix to NFC_PAGE_OP definition Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 09/57] evm: Don't deadlock if a crypto algorithm is unavailable Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 10/57] KVM: PPC: Book3S HV: Add of_node_put() in success path Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 12/57] PM / devfreq: use put_device() instead of kfree() Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 11/57] security: check for kstrdup() failure in lsm_append() Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 13/57] MIPS: loongson64: cs5536: Fix PCI_OHCI_INT_REG reads Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 14/57] configfs: fix registered group removal Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 15/57] pinctrl: rza1: Fix selector use for groups and functions Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 16/57] pinctrl: pinmux: Return selector to the pinctrl driver Sasha Levin
2018-09-15  1:32 ` Sasha Levin [this message]
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 19/57] ARM: hisi: handle of_iomap and fix missing of_node_put Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 18/57] efi/esrt: Only call efi_mem_reserve() for boot services memory Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 21/57] ARM: hisi: check of_iomap and fix missing of_node_put Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 20/57] ARM: hisi: fix error handling and " Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 22/57] liquidio: fix hang when re-binding VF host drv after running DPDK VF driver Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 23/57] gpu: ipu-v3: csi: pass back mbus_code_to_bus_cfg error codes Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 24/57] tty: fix termios input-speed encoding when using BOTHER Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 25/57] tty: fix termios input-speed encoding Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 27/57] mmc: tegra: prevent HS200 on Tegra 3 Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 26/57] mmc: sdhci-of-esdhc: set proper dma mask for ls104x chips Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 29/57] drm/nouveau: Fix runtime PM leak in drm_open() Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 28/57] mmc: sdhci: do not try to use 3.3V signaling if not supported Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 31/57] drm/nouveau: tegra: Detach from ARM DMA/IOMMU mapping Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 30/57] drm/nouveau/debugfs: Wake up GPU before doing any reclocking Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 32/57] parport: sunbpp: fix error return code Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 33/57] sched/fair: Fix util_avg of new tasks for asymmetric systems Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 34/57] coresight: Handle errors in finding input/output ports Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 36/57] coresight: ETM: Add support for Arm Cortex-A73 and Cortex-A35 Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 35/57] coresight: tpiu: Fix disabling timeouts Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 38/57] gpio: pxa: Fix potential NULL dereference Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 37/57] staging: bcm2835-audio: Don't leak workqueue if open fails Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 39/57] gpiolib: Mark gpio_suffixes array with __maybe_unused Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 40/57] mfd: 88pm860x-i2c: switch to i2c_lock_bus(..., I2C_LOCK_SEGMENT) Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 42/57] rcu: Fix grace-period hangs due to race with CPU offline Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 41/57] input: rohm_bu21023: switch to i2c_lock_bus(..., I2C_LOCK_SEGMENT) Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 43/57] drm/amdkfd: Fix error codes in kfd_get_process Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 45/57] ALSA: pcm: Fix snd_interval_refine first/last with open min/max Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 44/57] rtc: bq4802: add error handling for devm_ioremap Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 47/57] selftest: timers: Tweak raw_skew to SKIP when ADJ_OFFSET/other clock adjustments are in progress Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 46/57] scsi: libfc: fixup 'sleeping function called from invalid context' Sasha Levin
2018-09-15  1:32 ` [PATCH AUTOSEL 4.14 48/57] drm/panel: type promotion bug in s6e8aa0_read_mtp_id() Sasha Levin
2018-09-15  1:33 ` [PATCH AUTOSEL 4.14 49/57] dmaengine: hsu: Support dmaengine_terminate_sync() Sasha Levin
2018-09-15  1:33 ` [PATCH AUTOSEL 4.14 50/57] dmaengine: idma64: " Sasha Levin
2018-09-15  1:33 ` [PATCH AUTOSEL 4.14 51/57] IB/nes: Fix a compiler warning Sasha Levin
2018-09-15  1:33 ` [PATCH AUTOSEL 4.14 52/57] blk-mq: only attempt to merge bio if there is rq in sw queue Sasha Levin
2018-09-15  1:33 ` [PATCH AUTOSEL 4.14 54/57] gpiolib: Respect error code of ->get_direction() Sasha Levin
2018-09-15  1:33 ` [PATCH AUTOSEL 4.14 53/57] blk-mq: avoid to synchronize rcu inside blk_cleanup_queue() Sasha Levin
2018-09-15  1:33 ` [PATCH AUTOSEL 4.14 55/57] pinctrl: msm: Fix msm_config_group_get() to be compliant Sasha Levin
2018-09-15  1:33 ` [PATCH AUTOSEL 4.14 56/57] pinctrl: qcom: spmi-gpio: Fix pmic_gpio_config_get() " Sasha Levin
2018-09-15  1:33 ` [PATCH AUTOSEL 4.14 57/57] clk: tegra: bpmp: Don't crash when a clock fails to register Sasha Levin

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