This is a note to let you know that I've just added the patch titled
futex: fix dead code in attach_to_pi_owner()
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
futex-fix-dead-code-in-attach_to_pi_owner.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Fri Mar 12 11:10:32 AM CET 2021
From: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
Date: Thu, 11 Mar 2021 11:26:00 +0800
Subject: futex: fix dead code in attach_to_pi_owner()
To: <gregkh@xxxxxxxxxxxxxxxxxxx>, <lee.jones@xxxxxxxxxx>, <stable@xxxxxxxxxxxxxxx>, <linux-kernel@xxxxxxxxxxxxxxx>
Cc: <tglx@xxxxxxxxxxxxx>, <cj.chengjian@xxxxxxxxxx>, <judy.chenhui@xxxxxxxxxx>, <zhangjinhao2@xxxxxxxxxx>, <nixiaoming@xxxxxxxxxx>
Message-ID: <20210311032600.2326035-4-zhengyejian1@xxxxxxxxxx>
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
This patch comes directly from an origin patch (commit
91509e84949fc97e7424521c32a9e227746e0b85) in v4.9.
And it is part of a full patch which was originally back-ported
to v4.14 as commit e6e00df182908f34360c3c9f2d13cc719362e9c0
The handle_exit_race() function is defined in commit 9c3f39860367
("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.
Lee writes:
This commit takes the remaining functional snippet of:
ac31c7ff8624409 ("futex: Provide distinct return value when owner is exiting")
... and is the correct fix for this issue.
Fixes: 9c3f39860367 ("futex: Cure exit race")
Cc: stable@xxxxxxxxxxxxxxx # v4.9.258
Signed-off-by: Xiaoming Ni <nixiaoming@xxxxxxxxxx>
Reviewed-by: Lee Jones <lee.jones@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/futex.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1204,11 +1204,11 @@ static int handle_exit_race(u32 __user *
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:
Patches currently in stable-queue which might be from zhengyejian1@xxxxxxxxxx are
queue-4.4/futex-change-locking-rules.patch
queue-4.4/futex-fix-dead-code-in-attach_to_pi_owner.patch
queue-4.4/futex-cure-exit-race.patch
