Will Deacon d133166146 locking/qrwlock: Prevent slowpath writers getting held up by fastpath ... When a prospective writer takes the qrwlock locking slowpath due to the lock being held, it attempts to cmpxchg the wmode field from 0 to _QW_WAITING so that concurrent lockers also take the slowpath and queue on the spinlock accordingly, allowing the lockers to drain. Unfortunately, this isn't fair, because a fastpath writer that comes in after the lock is made available but before the _QW_WAITING flag is set can effectively jump the queue. If there is a steady stream of prospective writers, then the waiter will be held off indefinitely. This patch restores fairness by separating _QW_WAITING and _QW_LOCKED into two distinct fields: _QW_LOCKED continues to occupy the bottom byte of the lockword so that it can be cleared unconditionally when unlocking, but _QW_WAITING now occupies what used to be the bottom bit of the reader count. This then forces the slow-path for concurrent lockers. Tested-by: Waiman Long <longman@redhat.com> Tested-by: Jeremy Linton <jeremy.linton@arm.com> Tested-by: Adam Wallis <awallis@codeaurora.org> Tested-by: Jan Glauber <jglauber@cavium.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Jeremy.Linton@arm.com Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-arm-kernel@lists.infradead.org Link: http://lkml.kernel.org/r/1507810851-306-6-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>		2017-10-25 10:57:25 +02:00
..
bitops	bitops: Do not default to __clear_bit() for __clear_bit_unlock()	2016-03-21 10:50:48 +01:00
4level-fixup.h	asm-generic: introduce 5level-fixup.h	2017-03-09 11:48:47 -08:00
5level-fixup.h	asm-generic: introduce 5level-fixup.h	2017-03-09 11:48:47 -08:00
asm-offsets.h	asm-generic: Add common asm-offsets.h	2015-06-23 13:35:49 +09:00
asm-prototypes.h	asm-prototypes: Clear any CPP defines before declaring the functions	2017-01-05 12:57:42 +01:00
atomic-long.h	locking/atomic: Add atomic_cond_read_acquire()	2017-10-25 10:57:24 +02:00
atomic.h	openrisc: add optimized atomic operations	2017-02-25 04:14:06 +09:00
atomic64.h	locking/atomic: Fix atomic_set_release() for 'funny' architectures	2017-08-10 12:28:54 +02:00
audit_change_attr.h	audit: Modify a set of system calls in audit class definitions	2014-01-17 17:01:46 -05:00
audit_dir_write.h
audit_read.h
audit_signal.h
audit_write.h	audit: Modify a set of system calls in audit class definitions	2014-01-17 17:01:46 -05:00
barrier.h	locking/spinlock, arch: Update and fix spin_unlock_wait() implementations	2016-06-14 11:55:15 +02:00
bitops.h	arch: Prepare for smp_mb__{before,after}_atomic()	2014-04-18 11:40:30 +02:00
bitsperlong.h
bug.h	asm-generic/bug.h: declare struct pt_regs; before function prototype	2017-07-10 16:32:34 -07:00
bugs.h
cache.h
cacheflush.h
checksum.h	ipv4: Update parameters for csum_tcpudp_magic to their original types	2016-03-13 23:55:13 -04:00
clkdev.h	asm-generic: COMMON_CLK defines __clk_{get,put}	2014-09-25 18:00:45 -07:00
cmpxchg-local.h	LLVMLinux: Remove warning about returning an uninitialized variable	2014-04-09 13:44:35 -07:00
cmpxchg.h	asm-generic: cmpxchg: avoid warnings from macro-ized cmpxchg() implementations	2015-10-15 00:21:13 +02:00
current.h
delay.h
device.h
div64.h	__div64_32(): make it overridable at compile time	2015-11-16 14:42:12 -05:00
dma-contiguous.h	asm-generic: Add dma-contiguous.h	2014-09-22 13:35:51 +02:00
dma.h
early_ioremap.h	x86/mm: Extend early_memremap() support with additional attrs	2017-07-18 11:38:00 +02:00
emergency-restart.h
exec.h
export.h	modversions: treat symbol CRCs as 32 bit quantities	2017-02-03 08:28:25 -08:00
extable.h	add asm-generic/extable.h	2017-03-27 20:27:28 -04:00
fb.h
fixmap.h	asm-generic: Fix local variable shadow in __set_fixmap_offset	2016-02-16 15:10:44 +00:00
ftrace.h
futex.h	futex: Remove duplicated code and fix undefined behaviour	2017-08-25 22:49:59 +02:00
getorder.h
gpio.h	gpio: allow setting ARCH_NR_GPIOS from Kconfig	2016-02-19 00:22:54 +01:00
hardirq.h
hugetlb.h	mm/hugetlb: allow architectures to override huge_pte_clear()	2017-07-06 16:24:34 -07:00
hw_irq.h
ide_iops.h
int-ll64.h
io.h	x86/io: Remove xlate_dev_kmem_ptr() duplication	2017-07-24 11:18:21 +02:00
ioctl.h	include/asm-generic/ioctl.h: fix _IOC_TYPECHECK sparse error	2014-06-06 16:08:13 -07:00
iomap.h	asm-generic/io.h: add io{read,write}64 accessors	2016-05-31 16:41:50 +08:00
irq.h
irq_regs.h
irq_work.h	irq_work: Introduce arch_irq_work_has_interrupt()	2014-09-13 18:38:07 +02:00
irqflags.h
kdebug.h
kmap_types.h
kprobes.h	kprobes: move kprobe declarations to asm-generic/kprobes.h	2017-02-27 18:43:45 -08:00
kvm_para.h	KVM: add kvm_para_available to asm-generic/kvm_para.h	2013-06-05 13:21:29 +03:00
linkage.h
local.h
local64.h
mcs_spinlock.h	locking/mcs: Allow architecture specific asm files to be used for contended case	2014-02-09 21:18:52 +01:00
memory_model.h	mm: add PHYS_PFN, use it in __phys_to_pfn()	2016-01-14 16:00:49 -08:00
mm-arch-hooks.h	mm: clean up per architecture MM hook header files	2015-07-17 16:39:53 -07:00
mm_hooks.h	mm/gup: Drop the arch_pte_access_permitted() MMU callback	2017-03-18 09:48:01 +01:00
mmu.h
mmu_context.h	asm-generic: Remove asm-generic arch_bprm_mm_init()	2014-11-22 21:52:08 +01:00
module.h
msi.h	asm-generic: Add msi.h	2014-11-23 13:01:47 +01:00
page.h	asm-generic: page.h: Remove useless get_user_page and free_user_page	2016-02-26 15:24:55 +01:00
param.h
parport.h
pci.h	PCI: Remove unused pcibios_select_root() (again)	2015-06-08 07:56:21 -05:00
pci_iomap.h	PCI: Add pci_iomap_wc() variants	2015-08-25 09:59:45 +02:00
percpu.h	percpu: make this_cpu_generic_read() atomic w.r.t. interrupts	2017-09-26 07:37:33 -07:00
pgalloc.h
pgtable-nop4d-hack.h	asm-generic: introduce __ARCH_USE_5LEVEL_HACK	2017-03-09 11:48:47 -08:00
pgtable-nop4d.h	asm-generic: introduce <asm-generic/pgtable-nop4d.h>	2017-03-09 11:48:47 -08:00
pgtable-nopmd.h
pgtable-nopud.h	asm-generic: introduce <asm-generic/pgtable-nop4d.h>	2017-03-09 11:48:47 -08:00
pgtable.h	mm: soft-dirty: keep soft-dirty bits over thp migration	2017-09-08 18:26:45 -07:00
preempt.h	sched/preempt: Fix preempt_count manipulations	2016-05-17 12:24:21 +02:00
ptrace.h
qrwlock.h	locking/qrwlock: Prevent slowpath writers getting held up by fastpath	2017-10-25 10:57:25 +02:00
qrwlock_types.h	locking/qrwlock: Prevent slowpath writers getting held up by fastpath	2017-10-25 10:57:25 +02:00
qspinlock.h	locking/arch: Remove dummy arch_{read,spin,write}_lock_flags() implementations	2017-10-10 11:50:19 +02:00
qspinlock_types.h	locking/qspinlock: Move __ARCH_SPIN_LOCK_UNLOCKED to qspinlock_types.h	2016-02-29 10:02:43 +01:00
resource.h	asm-generic: remove _STK_LIM_MAX	2014-05-15 00:32:09 +01:00
rwsem.h	locking/rwsem: Add down_read_killable()	2017-10-10 11:50:16 +02:00
seccomp.h	seccomp: Get compat syscalls from asm-generic header	2016-05-13 14:02:00 +02:00
sections.h	irq: Make the irqentry text section unconditional	2017-08-10 16:28:53 +02:00
segment.h
serial.h
set_memory.h	treewide: move set_memory_* functions away from cacheflush.h	2017-05-08 17:15:13 -07:00
signal.h
simd.h	crypto: create generic version of ablk_helper	2013-09-24 06:02:24 +10:00
sizes.h
spinlock.h
statfs.h
string.h
switch_to.h
syscall.h	syscall.h: fix doc text for syscall_get_arch()	2014-09-23 16:20:00 -04:00
syscalls.h
termios-base.h	Replace <asm/uaccess.h> with <linux/uaccess.h> globally	2016-12-24 11:46:01 -08:00
termios.h	Replace <asm/uaccess.h> with <linux/uaccess.h> globally	2016-12-24 11:46:01 -08:00
timex.h
tlb.h	mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem	2017-08-10 15:54:07 -07:00
tlbflush.h
topology.h	cpumask: fix spurious cpumask_of_node() on non-NUMA multi-node configs	2017-08-28 16:13:16 -07:00
trace_clock.h
uaccess.h	fix the __user misannotations in asm-generic get_user/put_user	2017-09-04 12:07:24 -04:00
unaligned.h	asm-generic: allow generic unaligned access if the arch supports it	2014-05-08 10:22:23 +02:00
unistd.h
user.h
vga.h
vmlinux.lds.h	locking/refcounts, x86/asm: Use unique .text section for refcount exceptions	2017-09-28 09:45:05 +02:00
vtime.h	include/asm-generic/vtime.h: avoid zero-length file	2013-09-30 14:31:02 -07:00
word-at-a-time.h	Make asm/word-at-a-time.h available on all architectures	2015-07-08 16:41:55 -04:00
xor.h