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

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Date:   Thu, 11 Mar 2021 11:48:52 +0800
From:   "Zhengyejian (Zetta)" <zhengyejian1@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>
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 0/3] Backport patch series to update Futex from 4.9



On 2021/3/9 18:41, Greg KH wrote:
> On Tue, Mar 09, 2021 at 11:06:02AM +0800, Zheng Yejian wrote:
>> Lee sent a patchset to update Futex for 4.9, 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 patchsets may also resolve following issues in 4.4.260 which have been reported in 4.9,
>> 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.
> 
> There already are 2 futex patches in the 4.4.y stable queue, do those
> not resolve these issues for you?

I think that 2 futex patches in 4.4 stable queue are fixing other issues:
     futex-fix-irq-self-deadlock-and-satisfy-assertion.patch
     futex-fix-spin_lock-spin_unlock_irq-imbalance.patch
But I am not very sure if there are any lock conflicts between that 2 
patches and this 3 patches.

> 
> If not, please resend this series with the needed git commit ids added to
> them.

I have add that information and sent a "v2" patchset.