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authorLinus Torvalds <torvalds@linux-foundation.org>2021-08-31 00:26:36 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-08-31 00:26:36 +0300
commite5e726f7bb9f711102edea7e5bd511835640e3b4 (patch)
treee9f2d1696cd7a9664a04735568b2adbd2527e2e0 /lib
parent08403e2174c4ac8b23922b5b7abe670129f8acb5 (diff)
parenta055fcc132d4c25b96d1115aea514258810dc6fc (diff)
downloadlinux-e5e726f7bb9f711102edea7e5bd511835640e3b4.tar.xz
Merge tag 'locking-core-2021-08-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking and atomics updates from Thomas Gleixner: "The regular pile: - A few improvements to the mutex code - Documentation updates for atomics to clarify the difference between cmpxchg() and try_cmpxchg() and to explain the forward progress expectations. - Simplification of the atomics fallback generator - The addition of arch_atomic_long*() variants and generic arch_*() bitops based on them. - Add the missing might_sleep() invocations to the down*() operations of semaphores. The PREEMPT_RT locking core: - Scheduler updates to support the state preserving mechanism for 'sleeping' spin- and rwlocks on RT. This mechanism is carefully preserving the state of the task when blocking on a 'sleeping' spin- or rwlock and takes regular wake-ups targeted at the same task into account. The preserved or updated (via a regular wakeup) state is restored when the lock has been acquired. - Restructuring of the rtmutex code so it can be utilized and extended for the RT specific lock variants. - Restructuring of the ww_mutex code to allow sharing of the ww_mutex specific functionality for rtmutex based ww_mutexes. - Header file disentangling to allow substitution of the regular lock implementations with the PREEMPT_RT variants without creating an unmaintainable #ifdef mess. - Shared base code for the PREEMPT_RT specific rw_semaphore and rwlock implementations. Contrary to the regular rw_semaphores and rwlocks the PREEMPT_RT implementation is writer unfair because it is infeasible to do priority inheritance on multiple readers. Experience over the years has shown that real-time workloads are not the typical workloads which are sensitive to writer starvation. The alternative solution would be to allow only a single reader which has been tried and discarded as it is a major bottleneck especially for mmap_sem. Aside of that many of the writer starvation critical usage sites have been converted to a writer side mutex/spinlock and RCU read side protections in the past decade so that the issue is less prominent than it used to be. - The actual rtmutex based lock substitutions for PREEMPT_RT enabled kernels which affect mutex, ww_mutex, rw_semaphore, spinlock_t and rwlock_t. The spin/rw_lock*() functions disable migration across the critical section to preserve the existing semantics vs per-CPU variables. - Rework of the futex REQUEUE_PI mechanism to handle the case of early wake-ups which interleave with a re-queue operation to prevent the situation that a task would be blocked on both the rtmutex associated to the outer futex and the rtmutex based hash bucket spinlock. While this situation cannot happen on !RT enabled kernels the changes make the underlying concurrency problems easier to understand in general. As a result the difference between !RT and RT kernels is reduced to the handling of waiting for the critical section. !RT kernels simply spin-wait as before and RT kernels utilize rcu_wait(). - The substitution of local_lock for PREEMPT_RT with a spinlock which protects the critical section while staying preemptible. The CPU locality is established by disabling migration. The underlying concepts of this code have been in use in PREEMPT_RT for way more than a decade. The code has been refactored several times over the years and this final incarnation has been optimized once again to be as non-intrusive as possible, i.e. the RT specific parts are mostly isolated. It has been extensively tested in the 5.14-rt patch series and it has been verified that !RT kernels are not affected by these changes" * tag 'locking-core-2021-08-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (92 commits) locking/rtmutex: Return success on deadlock for ww_mutex waiters locking/rtmutex: Prevent spurious EDEADLK return caused by ww_mutexes locking/rtmutex: Dequeue waiter on ww_mutex deadlock locking/rtmutex: Dont dereference waiter lockless locking/semaphore: Add might_sleep() to down_*() family locking/ww_mutex: Initialize waiter.ww_ctx properly static_call: Update API documentation locking/local_lock: Add PREEMPT_RT support locking/spinlock/rt: Prepare for RT local_lock locking/rtmutex: Add adaptive spinwait mechanism locking/rtmutex: Implement equal priority lock stealing preempt: Adjust PREEMPT_LOCK_OFFSET for RT locking/rtmutex: Prevent lockdep false positive with PI futexes futex: Prevent requeue_pi() lock nesting issue on RT futex: Simplify handle_early_requeue_pi_wakeup() futex: Reorder sanity checks in futex_requeue() futex: Clarify comment in futex_requeue() futex: Restructure futex_requeue() futex: Correct the number of requeued waiters for PI futex: Remove bogus condition for requeue PI ...
Diffstat (limited to 'lib')
-rw-r--r--lib/Kconfig.debug11
-rw-r--r--lib/test_lockup.c8
2 files changed, 10 insertions, 9 deletions
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 5ddd575159fb..e5cdf98f50c2 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1235,7 +1235,7 @@ config PROVE_LOCKING
depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
select LOCKDEP
select DEBUG_SPINLOCK
- select DEBUG_MUTEXES
+ select DEBUG_MUTEXES if !PREEMPT_RT
select DEBUG_RT_MUTEXES if RT_MUTEXES
select DEBUG_RWSEMS
select DEBUG_WW_MUTEX_SLOWPATH
@@ -1299,7 +1299,7 @@ config LOCK_STAT
depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
select LOCKDEP
select DEBUG_SPINLOCK
- select DEBUG_MUTEXES
+ select DEBUG_MUTEXES if !PREEMPT_RT
select DEBUG_RT_MUTEXES if RT_MUTEXES
select DEBUG_LOCK_ALLOC
default n
@@ -1335,7 +1335,7 @@ config DEBUG_SPINLOCK
config DEBUG_MUTEXES
bool "Mutex debugging: basic checks"
- depends on DEBUG_KERNEL
+ depends on DEBUG_KERNEL && !PREEMPT_RT
help
This feature allows mutex semantics violations to be detected and
reported.
@@ -1345,7 +1345,8 @@ config DEBUG_WW_MUTEX_SLOWPATH
depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
select DEBUG_LOCK_ALLOC
select DEBUG_SPINLOCK
- select DEBUG_MUTEXES
+ select DEBUG_MUTEXES if !PREEMPT_RT
+ select DEBUG_RT_MUTEXES if PREEMPT_RT
help
This feature enables slowpath testing for w/w mutex users by
injecting additional -EDEADLK wound/backoff cases. Together with
@@ -1368,7 +1369,7 @@ config DEBUG_LOCK_ALLOC
bool "Lock debugging: detect incorrect freeing of live locks"
depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
select DEBUG_SPINLOCK
- select DEBUG_MUTEXES
+ select DEBUG_MUTEXES if !PREEMPT_RT
select DEBUG_RT_MUTEXES if RT_MUTEXES
select LOCKDEP
help
diff --git a/lib/test_lockup.c b/lib/test_lockup.c
index 864554e76973..906b598740a7 100644
--- a/lib/test_lockup.c
+++ b/lib/test_lockup.c
@@ -485,13 +485,13 @@ static int __init test_lockup_init(void)
offsetof(spinlock_t, lock.wait_lock.magic),
SPINLOCK_MAGIC) ||
test_magic(lock_rwlock_ptr,
- offsetof(rwlock_t, rtmutex.wait_lock.magic),
+ offsetof(rwlock_t, rwbase.rtmutex.wait_lock.magic),
SPINLOCK_MAGIC) ||
test_magic(lock_mutex_ptr,
- offsetof(struct mutex, lock.wait_lock.magic),
+ offsetof(struct mutex, rtmutex.wait_lock.magic),
SPINLOCK_MAGIC) ||
test_magic(lock_rwsem_ptr,
- offsetof(struct rw_semaphore, rtmutex.wait_lock.magic),
+ offsetof(struct rw_semaphore, rwbase.rtmutex.wait_lock.magic),
SPINLOCK_MAGIC))
return -EINVAL;
#else
@@ -502,7 +502,7 @@ static int __init test_lockup_init(void)
offsetof(rwlock_t, magic),
RWLOCK_MAGIC) ||
test_magic(lock_mutex_ptr,
- offsetof(struct mutex, wait_lock.rlock.magic),
+ offsetof(struct mutex, wait_lock.magic),
SPINLOCK_MAGIC) ||
test_magic(lock_rwsem_ptr,
offsetof(struct rw_semaphore, wait_lock.magic),