linux-kernel - Re: [PATCH 4.4 v2 0/3] Backport patch series to update Futex from 4.9

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Date:   Fri, 12 Mar 2021 14:26:32 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zheng Yejian <zhengyejian1@...wei.com>
Cc:     lee.jones@...aro.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        cj.chengjian@...wei.com, judy.chenhui@...wei.com,
        zhangjinhao2@...wei.com, nixiaoming@...wei.com
Subject: Re: [PATCH 4.4 v2 0/3] Backport patch series to update Futex from 4.9

On Thu, Mar 11, 2021 at 11:25:57AM +0800, Zheng Yejian wrote:
> Changelog for 'v2':
>   Complete commit messages with needed git commit ids as Greg and Lee suggested.
> 
> Lee sent a patchset to update Futex for v4.9, see https://www.spinics.net/lists/stable/msg443081.html,
> Then Xiaoming sent a follow-up patch for it, see https://lore.kernel.org/lkml/20210225093120.GD641347@dell/.
> 
> These 3 patches is directly picked from v4.9,
> and they may also resolve following issues in 4.4.260 which have been reported in v4.9,
> see https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/?h=linux-4.4.y&id=319f66f08de1083c1fe271261665c209009dd65a
>       > /*
>       >  * The task is on the way out. When the futex state is
>       >  * FUTEX_STATE_DEAD, we know that the task has finished
>       >  * the cleanup:
>       >  */
>       > int ret = (p->futex_state = FUTEX_STATE_DEAD) ? -ESRCH : -EAGAIN;
> 
>     Here may be:
>       int ret = (p->futex_state == FUTEX_STATE_DEAD) ? -ESRCH : -EAGAIN;
> 
>       > raw_spin_unlock_irq(&p->pi_lock);
>       > /*
>       >  * If the owner task is between FUTEX_STATE_EXITING and
>       >  * FUTEX_STATE_DEAD then store the task pointer and keep
>       >  * the reference on the task struct. The calling code will
>       >  * drop all locks, wait for the task to reach
>       >  * FUTEX_STATE_DEAD and then drop the refcount. This is
>       >  * required to prevent a live lock when the current task
>       >  * preempted the exiting task between the two states.
>       >  */
>       > if (ret == -EBUSY)
> 
>     And here, the variable "ret" may only be "-ESRCH" or "-EAGAIN", but not "-EBUSY".
> 
>       > 	*exiting = p;
>       > else
>       > 	put_task_struct(p);
> 
> Since 074e7d515783 ("futex: Ensure the correct return value from futex_lock_pi()") has
> been merged in 4.4.260, I send the remain 3 patches.
> 
> Peter Zijlstra (1):
>   futex: Change locking rules
> 
> Thomas Gleixner (2):
>   futex: Cure exit race
>   futex: fix dead code in attach_to_pi_owner()
> 
>  kernel/futex.c | 209 +++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 177 insertions(+), 32 deletions(-)

All now queued up, thanks.

greg k-h