[08/12] futex: Sanitize exit state handling

Message ID	20210201151214.2193508-9-lee.jones@linaro.org
State	New
Headers	show Delivered-To: patch@linaro.org Received-SPF: pass (google.com: domain of stable-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; From: Lee Jones <lee.jones@linaro.org> To: stable@vger.kernel.org Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Lee Jones <lee.jones@linaro.org> Subject: [PATCH 08/12] futex: Sanitize exit state handling Date: Mon, 1 Feb 2021 15:12:10 +0000 Message-Id: <20210201151214.2193508-9-lee.jones@linaro.org> In-Reply-To: <20210201151214.2193508-1-lee.jones@linaro.org> References: <20210201151214.2193508-1-lee.jones@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk
Series	Futex back-port from v4.9 \| expand [4.4,00/12] Futex back-port from v4.9 [01/12] y2038: futex: Move compat implementation into futex.c [02/12] futex: Move futex exit handling into futex code [03/12] futex: Replace PF_EXITPIDONE with a state [04/12] exit/exec: Seperate mm_release() [05/12] futex: Split futex_mm_release() for exit/exec [06/12] futex: Set task::futex_state to DEAD right after handling futex exit [07/12] futex: Mark the begin of futex exit explicitly [08/12] futex: Sanitize exit state handling [09/12] futex: Provide state handling for exec() as well [10/12] futex: Add mutex around futex exit [11/12] futex: Provide distinct return value when owner is exiting [12/12] futex: Prevent exit livelock

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20210201151214.2193508-9-lee.jones@linaro.org

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Received-SPF: pass (google.com: domain of stable-owner@vger.kernel.org
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From: Lee Jones <lee.jones@linaro.org>
To: stable@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Lee Jones <lee.jones@linaro.org>
Subject: [PATCH 08/12] futex: Sanitize exit state handling
Date: Mon,  1 Feb 2021 15:12:10 +0000
Message-Id: <20210201151214.2193508-9-lee.jones@linaro.org>
In-Reply-To: <20210201151214.2193508-1-lee.jones@linaro.org>
References: <20210201151214.2193508-1-lee.jones@linaro.org>
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Series

Futex back-port from v4.9 | expand

Commit Message

Lee Jones Feb. 1, 2021, 3:12 p.m. UTC

From: Thomas Gleixner <tglx@linutronix.de>


commit 4a8e991b91aca9e20705d434677ac013974e0e30 upstream.

Instead of having a smp_mb() and an empty lock/unlock of task::pi_lock move
the state setting into to the lock section.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Reviewed-by: Ingo Molnar <mingo@kernel.org>

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Link: https://lkml.kernel.org/r/20191106224556.645603214@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Lee Jones <lee.jones@linaro.org>

---
 kernel/futex.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

-- 
2.25.1

diff --git a/kernel/futex.c b/kernel/futex.c
index 5bd3afee4e139..0efcb55455c2a 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3276,16 +3276,19 @@  void futex_exit_recursive(struct task_struct *tsk)
 
 void futex_exit_release(struct task_struct *tsk)
 {
-	tsk->futex_state = FUTEX_STATE_EXITING;
-	/*
-	 * Ensure that all new tsk->pi_lock acquisitions must observe
-	 * FUTEX_STATE_EXITING. Serializes against attach_to_pi_owner().
-	 */
-	smp_mb();
 	/*
-	 * Ensure that we must observe the pi_state in exit_pi_state_list().
+	 * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
+	 *
+	 * This ensures that all subsequent checks of tsk->futex_state in
+	 * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
+	 * tsk->pi_lock held.
+	 *
+	 * It guarantees also that a pi_state which was queued right before
+	 * the state change under tsk->pi_lock by a concurrent waiter must
+	 * be observed in exit_pi_state_list().
 	 */
 	raw_spin_lock_irq(&tsk->pi_lock);
+	tsk->futex_state = FUTEX_STATE_EXITING;
 	raw_spin_unlock_irq(&tsk->pi_lock);
 
 	futex_exec_release(tsk);

[08/12] futex: Sanitize exit state handling

Commit Message

Patch