On Mon, Aug 02, 2021 at 09:46:13PM +0800, Zhen Lei wrote:
Commit 73d786bd043e "futex: Rework inconsistent rt_mutex/futex_q state" mentions that it could cause an infinite loop, and will fix it in the later patches: bebe5b514345f09 futex: Futex_unlock_pi() determinism cfafcd117da0216 futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock()
But at the moment they're not backported. In a single-core environment, the probability of triggering is high.
I also backported commit b4abf91047cf ("rtmutex: Make wait_lock irq safe"), it fixes a potential deadlock problem. Although it hasn't actually been triggered in our environment at the moment.
Other patches are used to resolve conflicts or fix problems caused by new patches.
Anna-Maria Gleixner (1): rcu: Update documentation of rcu_read_unlock()
Mike Galbraith (1): futex: Handle transient "ownerless" rtmutex state correctly
Peter Zijlstra (6): futex: Cleanup refcounting futex,rt_mutex: Introduce rt_mutex_init_waiter() futex: Pull rt_mutex_futex_unlock() out from under hb->lock futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock() futex: Futex_unlock_pi() determinism futex,rt_mutex: Fix rt_mutex_cleanup_proxy_lock()
Thomas Gleixner (3): futex: Rename free_pi_state() to put_pi_state() rtmutex: Make wait_lock irq safe futex: Avoid freeing an active timer
include/linux/rcupdate.h | 4 +- kernel/futex.c | 245 +++++++++++++++++++++----------- kernel/locking/rtmutex.c | 185 +++++++++++++----------- kernel/locking/rtmutex_common.h | 2 +- 4 files changed, 262 insertions(+), 174 deletions(-)
To all concerned,
I have verified that this series of patches, when applied to 4.4.277, passes the futex-unlock-pi replicator I posted to lkml on July 19.
Subject: [BUG] 4.4.262: infinite loop in futex_unlock_pi (EAGAIN loop)
Acked-by: Joe Korty joe.korty@concurrent-rt.com