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Subject[PATCH 4.4 v2 0/3] Backport patch series to update Futex from 4.9
Date
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

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