linux-kernel - [PATCH] futex: fix dead code in attach_to_pi

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Message-ID: <20210222125352.110124-1-nixiaoming@huawei.com>
Date:   Mon, 22 Feb 2021 20:53:52 +0800
From:   Xiaoming Ni <nixiaoming@...wei.com>
To:     <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
        <gregkh@...uxfoundation.org>, <sashal@...nel.org>,
        <tglx@...utronix.de>, <lee.jones@...aro.org>
CC:     <nixiaoming@...wei.com>, <wangle6@...wei.com>,
        <zhengyejian1@...wei.com>
Subject: [PATCH] futex: fix dead code in attach_to_pi_owner()

From: Thomas Gleixner <tglx@...utronix.de>

The handle_exit_race() function is defined in commit c158b461306df82
 ("futex: Cure exit race"), which never returns -EBUSY. This results
in a small piece of dead code in the attach_to_pi_owner() function:

	int ret = handle_exit_race(uaddr, uval, p); /* Never return -EBUSY */
	...
	if (ret == -EBUSY)
		*exiting = p; /* dead code */

The return value -EBUSY is added to handle_exit_race() in upsteam
commit ac31c7ff8624409 ("futex: Provide distinct return value when
owner is exiting"). This commit was incorporated into v4.9.255, before
the function handle_exit_race() was introduced, whitout Modify
handle_exit_race().

To fix dead code, extract the change of handle_exit_race() from
commit ac31c7ff8624409 ("futex: Provide distinct return value when owner
 is exiting"), re-incorporated.

Fixes: c158b461306df82 ("futex: Cure exit race")
Cc: stable@...r.kernel.org # 4.9.258-rc1
Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
---
 kernel/futex.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index b65dbb5d60bb..0fd785410150 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1207,11 +1207,11 @@ static int handle_exit_race(u32 __user *uaddr, u32 uval,
 	u32 uval2;

 	/*
-	 * If the futex exit state is not yet FUTEX_STATE_DEAD, wait
-	 * for it to finish.
+	 * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
+	 * caller that the alleged owner is busy.
 	 */
 	if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
-		return -EAGAIN;
+		return -EBUSY;

 	/*
 	 * Reread the user space value to handle the following situation:
-- 
2.27.0