Re: [PATCH 4.4 3/3] futex: fix dead code in attach_to_pi_owner()

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On 2021/3/10 22:10, Greg KH wrote:
On Wed, Mar 10, 2021 at 01:28:02PM +0000, Lee Jones wrote:
On Wed, 10 Mar 2021, Greg KH wrote:

On Tue, Mar 09, 2021 at 06:14:37PM +0000, Lee Jones wrote:
On Tue, 09 Mar 2021, Greg KH wrote:

On Tue, Mar 09, 2021 at 11:06:05AM +0800, Zheng Yejian wrote:
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

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>
---
  kernel/futex.c | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

Same here, what is the upstream git id?

It doesn't have one as such - it's a part-patch:

This commit takes the remaining functional snippet of:

  ac31c7ff8624409 ("futex: Provide distinct return value when owner is exiting")

That wasn't obvious :(

This was also my thinking, which is why I replied to the original
patch in an attempt to clarify what I thought was happening.

Is this a backport of another patch in the stable tree somewhere?

Yes, it looks like it.

The full patch was back-ported to v4.14 as:

   e6e00df182908f34360c3c9f2d13cc719362e9c0

Ok, Zheng, can you put this information in the patch and resend the
whole series?


Sure, I'll send a "v2" patchset soon.
Thanks for your suggestions,

Zheng Yejian



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