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

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Date:   Thu, 11 Mar 2021 11:25:57 +0800
From:   Zheng Yejian <zhengyejian1@...wei.com>
To:     <gregkh@...uxfoundation.org>, <lee.jones@...aro.org>,
        <stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <tglx@...utronix.de>, <cj.chengjian@...wei.com>,
        <judy.chenhui@...wei.com>, <zhangjinhao2@...wei.com>,
        <nixiaoming@...wei.com>
Subject: [PATCH 4.4 v2 0/3] Backport patch series to update Futex from 4.9

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(-)

-- 
2.25.4