user/sven/linux.git/include/linux/rwsem.h, branch v5.4.90

rwsem: Implement down_read_interruptible

2021-01-09T12:44:55Z

[ Upstream commit 31784cff7ee073b34d6eddabb95e3be2880a425c ] In preparation for converting exec_update_mutex to a rwsem so that multiple readers can execute in parallel and not deadlock, add down_read_interruptible. This is needed for perf_event_open to be converted (with no semantic changes) from working on a mutex to wroking on a rwsem. Signed-off-by: Eric W. Biederman Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/87k0tybqfy.fsf@x220.int.ebiederm.org Signed-off-by: Sasha Levin

rwsem: Implement down_read_killable_nested

2021-01-09T12:44:55Z

[ Upstream commit 0f9368b5bf6db0c04afc5454b1be79022a681615 ] In preparation for converting exec_update_mutex to a rwsem so that multiple readers can execute in parallel and not deadlock, add down_read_killable_nested. This is needed so that kcmp_lock can be converted from working on a mutexes to working on rw_semaphores. Signed-off-by: Eric W. Biederman Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/87o8jabqh3.fsf@x220.int.ebiederm.org Signed-off-by: Sasha Levin

locking/rwsem: Check for operations on an uninitialized rwsem

2019-08-06T10:49:15Z

Currently rwsems is the only locking primitive that lacks this debug feature. Add it under CONFIG_DEBUG_RWSEMS and do the magic checking in the locking fastpath (trylock) operation such that we cover all cases. The unlocking part is pretty straightforward. Signed-off-by: Davidlohr Bueso Signed-off-by: Peter Zijlstra (Intel) Acked-by: Waiman Long Cc: mingo@kernel.org Cc: Davidlohr Bueso Link: https://lkml.kernel.org/r/20190729044735.9632-1-dave@stgolabs.net

docs: locking: convert docs to ReST and rename to *.rst

2019-07-15T11:53:27Z

Convert the locking documents to ReST and add them to the kernel development book where it belongs. Most of the stuff here is just to make Sphinx to properly parse the text file, as they're already in good shape, not requiring massive changes in order to be parsed. The conversion is actually: - add blank lines and identation in order to identify paragraphs; - fix tables markups; - add some lists markups; - mark literal blocks; - adjust title markups. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab Acked-by: Federico Vaga

locking/rwsem: Make rwsem->owner an atomic_long_t

2019-06-17T10:28:06Z

The rwsem->owner contains not just the task structure pointer, it also holds some flags for storing the current state of the rwsem. Some of the flags may have to be atomically updated. To reflect the new reality, the owner is now changed to an atomic_long_t type. New helper functions are added to properly separate out the task structure pointer and the embedded flags. Suggested-by: Peter Zijlstra Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Cc: Borislav Petkov Cc: Davidlohr Bueso Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Thomas Gleixner Cc: Tim Chen Cc: Will Deacon Cc: huang ying Link: https://lkml.kernel.org/r/20190520205918.22251-14-longman@redhat.com Signed-off-by: Ingo Molnar

locking/rwsem: Clarify usage of owner's nonspinaable bit

2019-06-17T10:28:03Z

Bit 1 of sem->owner (RWSEM_ANONYMOUSLY_OWNED) is used to designate an anonymous owner - readers or an anonymous writer. The setting of this anonymous bit is used as an indicator that optimistic spinning cannot be done on this rwsem. With the upcoming reader optimistic spinning patches, a reader-owned rwsem can be spinned on for a limit period of time. We still need this bit to indicate a rwsem is nonspinnable, but not setting this bit loses its meaning that the owner is known. So rename the bit to RWSEM_NONSPINNABLE to clarify its meaning. This patch also fixes a DEBUG_RWSEMS_WARN_ON() bug in __up_write(). Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Cc: Borislav Petkov Cc: Davidlohr Bueso Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Tim Chen Cc: Will Deacon Cc: huang ying Link: https://lkml.kernel.org/r/20190520205918.22251-12-longman@redhat.com Signed-off-by: Ingo Molnar

locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER

2019-06-17T10:27:54Z

The owner field in the rw_semaphore structure is used primarily for optimistic spinning. However, identifying the rwsem owner can also be helpful in debugging as well as tracing locking related issues when analyzing crash dump. The owner field may also store state information that can be important to the operation of the rwsem. So the owner field is now made a permanent member of the rw_semaphore structure irrespective of CONFIG_RWSEM_SPIN_ON_OWNER. Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Cc: Borislav Petkov Cc: Davidlohr Bueso Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Tim Chen Cc: Will Deacon Cc: huang ying Link: https://lkml.kernel.org/r/20190520205918.22251-2-longman@redhat.com Signed-off-by: Ingo Molnar

locking/rwsem: Optimize rwsem structure for uncontended lock acquisition

2019-04-10T08:56:06Z

For an uncontended rwsem, count and owner are the only fields a task needs to touch when acquiring the rwsem. So they are put next to each other to increase the chance that they will share the same cacheline. On a ThunderX2 99xx (arm64) system with 32K L1 cache and 256K L2 cache, a rwsem locking microbenchmark with one locking thread was run to write-lock and write-unlock an array of rwsems separated 2 cachelines apart in a 1M byte memory block. The locking rates (kops/s) of the microbenchmark when the rwsems are at various "long" (8-byte) offsets from beginning of the cacheline before and after the patch were as follows: Cacheline Offset Pre-patch Post-patch ---------------- --------- ---------- 0 17,449 16,588 1 17,450 16,465 2 17,450 16,460 3 17,453 16,462 4 14,867 16,471 5 14,867 16,470 6 14,853 16,464 7 14,867 13,172 Before the patch, the count and owner are 4 "long"s apart. After the patch, they are only 1 "long" apart. The rwsem data have to be loaded from the L3 cache for each access. It can be seen that the locking rates are more consistent after the patch than before. Note that for this particular system, the performance drop happens whenever the count and owner are at an odd multiples of "long"s apart. No performance drop was observed when only a single rwsem was used (hot cache). So the drop is likely just an idiosyncrasy of the cache architecture of this chip than an inherent problem with the patch. Suggested-by: Linus Torvalds Signed-off-by: Waiman Long Acked-by: Peter Zijlstra Cc: Andrew Morton Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Davidlohr Bueso Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Tim Chen Cc: Will Deacon Link: http://lkml.kernel.org/r/20190404174320.22416-12-longman@redhat.com Signed-off-by: Ingo Molnar

locking/rwsem: Move rwsem internal function declarations to rwsem-xadd.h

2019-04-10T08:56:00Z

We don't need to expose rwsem internal functions which are not supposed to be called directly from other kernel code. Signed-off-by: Waiman Long Acked-by: Peter Zijlstra Acked-by: Will Deacon Acked-by: Davidlohr Bueso Cc: Andrew Morton Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Davidlohr Bueso Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Tim Chen Link: http://lkml.kernel.org/r/20190404174320.22416-4-longman@redhat.com Signed-off-by: Ingo Molnar

locking/rwsem: Remove rwsem-spinlock.c & use rwsem-xadd.c for all archs

2019-04-03T12:50:52Z

Currently, we have two different implementation of rwsem: 1) CONFIG_RWSEM_GENERIC_SPINLOCK (rwsem-spinlock.c) 2) CONFIG_RWSEM_XCHGADD_ALGORITHM (rwsem-xadd.c) As we are going to use a single generic implementation for rwsem-xadd.c and no architecture-specific code will be needed, there is no point in keeping two different implementations of rwsem. In most cases, the performance of rwsem-spinlock.c will be worse. It also doesn't get all the performance tuning and optimizations that had been implemented in rwsem-xadd.c over the years. For simplication, we are going to remove rwsem-spinlock.c and make all architectures use a single implementation of rwsem - rwsem-xadd.c. All references to RWSEM_GENERIC_SPINLOCK and RWSEM_XCHGADD_ALGORITHM in the code are removed. Suggested-by: Peter Zijlstra Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Acked-by: Linus Torvalds Cc: Andrew Morton Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Davidlohr Bueso Cc: H. Peter Anvin Cc: Paul E. McKenney Cc: Thomas Gleixner Cc: Tim Chen Cc: Will Deacon Cc: linux-arm-kernel@lists.infradead.org Cc: linux-c6x-dev@linux-c6x.org Cc: linux-m68k@lists.linux-m68k.org Cc: linux-riscv@lists.infradead.org Cc: linux-um@lists.infradead.org Cc: linux-xtensa@linux-xtensa.org Cc: linuxppc-dev@lists.ozlabs.org Cc: nios2-dev@lists.rocketboards.org Cc: openrisc@lists.librecores.org Cc: uclinux-h8-devel@lists.sourceforge.jp Link: https://lkml.kernel.org/r/20190322143008.21313-3-longman@redhat.com Signed-off-by: Ingo Molnar