user/sven/linux.git/kernel/locking, branch v5.0.2

futex: Handle early deadlock return correctly

2019-02-08T12:00:36Z

commit 56222b212e8e ("futex: Drop hb->lock before enqueueing on the rtmutex") changed the locking rules in the futex code so that the hash bucket lock is not longer held while the waiter is enqueued into the rtmutex wait list. This made the lock and the unlock path symmetric, but unfortunately the possible early exit from __rt_mutex_proxy_start() due to a detected deadlock was not updated accordingly. That allows a concurrent unlocker to observe inconsitent state which triggers the warning in the unlock path. futex_lock_pi() futex_unlock_pi() lock(hb->lock) queue(hb_waiter) lock(hb->lock) lock(rtmutex->wait_lock) unlock(hb->lock) // acquired hb->lock hb_waiter = futex_top_waiter() lock(rtmutex->wait_lock) __rt_mutex_proxy_start() ---> fail remove(rtmutex_waiter); ---> returns -EDEADLOCK unlock(rtmutex->wait_lock) // acquired wait_lock wake_futex_pi() rt_mutex_next_owner() --> returns NULL --> WARN lock(hb->lock) unqueue(hb_waiter) The problem is caused by the remove(rtmutex_waiter) in the failure case of __rt_mutex_proxy_start() as this lets the unlocker observe a waiter in the hash bucket but no waiter on the rtmutex, i.e. inconsistent state. The original commit handles this correctly for the other early return cases (timeout, signal) by delaying the removal of the rtmutex waiter until the returning task reacquired the hash bucket lock. Treat the failure case of __rt_mutex_proxy_start() in the same way and let the existing cleanup code handle the eventual handover of the rtmutex gracefully. The regular rt_mutex_proxy_start() gains the rtmutex waiter removal for the failure case, so that the other callsites are still operating correctly. Add proper comments to the code so all these details are fully documented. Thanks to Peter for helping with the analysis and writing the really valuable code comments. Fixes: 56222b212e8e ("futex: Drop hb->lock before enqueueing on the rtmutex") Reported-by: Heiko Carstens Co-developed-by: Peter Zijlstra Signed-off-by: Peter Zijlstra Signed-off-by: Thomas Gleixner Tested-by: Heiko Carstens Cc: Martin Schwidefsky Cc: linux-s390@vger.kernel.org Cc: Stefan Liebler Cc: Sebastian Sewior Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1901292311410.1950@nanos.tec.linutronix.de

locking/rwsem: Fix (possible) missed wakeup

2019-01-21T10:15:39Z

Because wake_q_add() can imply an immediate wakeup (cmpxchg failure case), we must not rely on the wakeup being delayed. However, commit: e38513905eea ("locking/rwsem: Rework zeroing reader waiter->task") relies on exactly that behaviour in that the wakeup must not happen until after we clear waiter->task. [ peterz: Added changelog. ] Signed-off-by: Xie Yongji Signed-off-by: Zhang Yu Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: e38513905eea ("locking/rwsem: Rework zeroing reader waiter->task") Link: https://lkml.kernel.org/r/1543495830-2644-1-git-send-email-xieyongji@baidu.com Signed-off-by: Ingo Molnar

kernel/locking/mutex.c: remove caller signal_pending branch predictions

2019-01-04T21:13:48Z

This is already done for us internally by the signal machinery. Link: http://lkml.kernel.org/r/20181116002713.8474-2-dave@stgolabs.net Signed-off-by: Davidlohr Bueso Reviewed-by: Andrew Morton Cc: Peter Zijlstra Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2018-12-26T22:25:52Z

Pull locking updates from Ingo Molnar: "The main change in this cycle are initial preparatory bits of dynamic lockdep keys support from Bart Van Assche. There are also misc changes, a comment cleanup and a data structure cleanup" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: sched/fair: Clean up comment in nohz_idle_balance() locking/lockdep: Stop using RCU primitives to access 'all_lock_classes' locking/lockdep: Make concurrent lockdep_reset_lock() calls safe locking/lockdep: Remove a superfluous INIT_LIST_HEAD() statement locking/lockdep: Introduce lock_class_cache_is_registered() locking/lockdep: Inline __lockdep_init_map() locking/lockdep: Declare local symbols static tools/lib/lockdep/tests: Test the lockdep_reset_lock() implementation tools/lib/lockdep: Add dummy print_irqtrace_events() implementation tools/lib/lockdep: Rename "trywlock" into "trywrlock" tools/lib/lockdep/tests: Run lockdep tests a second time under Valgrind tools/lib/lockdep/tests: Improve testing accuracy tools/lib/lockdep/tests: Fix shellcheck warnings tools/lib/lockdep/tests: Display compiler warning and error messages locking/lockdep: Remove ::version from lock_class structure

locking/lockdep: Stop using RCU primitives to access 'all_lock_classes'

2018-12-11T13:54:56Z

Due to the previous patch all code that accesses the 'all_lock_classes' list holds the graph lock. Hence use regular list primitives instead of their RCU variants to access this list. Signed-off-by: Bart Van Assche Signed-off-by: Peter Zijlstra (Intel) Cc: Johannes Berg Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Sasha Levin Cc: Thomas Gleixner Cc: Waiman Long Cc: johannes.berg@intel.com Cc: tj@kernel.org Link: https://lkml.kernel.org/r/20181207011148.251812-14-bvanassche@acm.org Signed-off-by: Ingo Molnar

locking/lockdep: Make concurrent lockdep_reset_lock() calls safe

2018-12-11T13:54:55Z

Since zap_class() removes items from the all_lock_classes list and the classhash_table, protect all zap_class() calls against concurrent data structure modifications with the graph lock. Signed-off-by: Bart Van Assche Signed-off-by: Peter Zijlstra (Intel) Cc: Johannes Berg Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Sasha Levin Cc: Thomas Gleixner Cc: Waiman Long Cc: johannes.berg@intel.com Cc: tj@kernel.org Link: https://lkml.kernel.org/r/20181207011148.251812-13-bvanassche@acm.org Signed-off-by: Ingo Molnar

locking/lockdep: Remove a superfluous INIT_LIST_HEAD() statement

2018-12-11T13:54:54Z

Initializing a list entry just before it is passed to list_add_tail_rcu() is not necessary because list_add_tail_rcu() overwrites the next and prev pointers anyway. Hence remove the INIT_LIST_HEAD() statement. Signed-off-by: Bart Van Assche Signed-off-by: Peter Zijlstra (Intel) Cc: Johannes Berg Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Sasha Levin Cc: Thomas Gleixner Cc: Waiman Long Cc: johannes.berg@intel.com Cc: tj@kernel.org Link: https://lkml.kernel.org/r/20181207011148.251812-12-bvanassche@acm.org Signed-off-by: Ingo Molnar

locking/lockdep: Introduce lock_class_cache_is_registered()

2018-12-11T13:54:53Z

This patch does not change any functionality but makes the lockdep_reset_lock() function easier to read. Signed-off-by: Bart Van Assche Signed-off-by: Peter Zijlstra (Intel) Cc: Johannes Berg Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Sasha Levin Cc: Thomas Gleixner Cc: Waiman Long Cc: johannes.berg@intel.com Cc: tj@kernel.org Link: https://lkml.kernel.org/r/20181207011148.251812-11-bvanassche@acm.org Signed-off-by: Ingo Molnar

locking/lockdep: Inline __lockdep_init_map()

2018-12-11T13:54:51Z

Since the function __lockdep_init_map() only has one caller, inline it into its caller. This patch does not change any functionality. Signed-off-by: Bart Van Assche Signed-off-by: Peter Zijlstra (Intel) Cc: Johannes Berg Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Sasha Levin Cc: Thomas Gleixner Cc: Waiman Long Cc: johannes.berg@intel.com Cc: tj@kernel.org Link: https://lkml.kernel.org/r/20181207011148.251812-10-bvanassche@acm.org Signed-off-by: Ingo Molnar

locking/lockdep: Declare local symbols static

2018-12-11T13:54:51Z

This patch avoids that sparse complains about a missing declaration for the lock_classes array when building with CONFIG_DEBUG_LOCKDEP=n. Signed-off-by: Bart Van Assche Signed-off-by: Peter Zijlstra (Intel) Cc: Johannes Berg Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Sasha Levin Cc: Thomas Gleixner Cc: Waiman Long Cc: johannes.berg@intel.com Cc: tj@kernel.org Link: https://lkml.kernel.org/r/20181207011148.251812-9-bvanassche@acm.org Signed-off-by: Ingo Molnar