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futex: fix dead code in attach_to_pi_owner()

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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@vger.kernel.org # v4.9.258
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Reviewed-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Thomas Gleixner 2021-02-24 18:09:23 +08:00 committed by Greg Kroah-Hartman
parent 0d351804d4
commit 91509e8494
1 changed files with 3 additions and 3 deletions
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6
kernel/futex.c
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@ -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: