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