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=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(>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.
Re: [PATCH 4.4 0/3] Backport patch series to update Futex from 4.9
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=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(>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?
If not, please resend this series with the needed git commit ids added to
them.
thanks,
greg k-h
[PATCH 4.4 0/3] Backport patch series to update Futex from 4.9
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=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(>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
