Commit 23e8fe2e authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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

Pull RCU updates from Ingo Molnar:
 "The main RCU changes in this cycle are:

   - Documentation updates.

   - Miscellaneous fixes.

   - Preemptible-RCU fixes, including fixing an old bug in the
     interaction of RCU priority boosting and CPU hotplug.

   - SRCU updates.

   - RCU CPU stall-warning updates.

   - RCU torture-test updates"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (54 commits)
  rcu: Initialize tiny RCU stall-warning timeouts at boot
  rcu: Fix RCU CPU stall detection in tiny implementation
  rcu: Add GP-kthread-starvation checks to CPU stall warnings
  rcu: Make cond_resched_rcu_qs() apply to normal RCU flavors
  rcu: Optionally run grace-period kthreads at real-time priority
  ksoftirqd: Use new cond_resched_rcu_qs() function
  ksoftirqd: Enable IRQs and call cond_resched() before poking RCU
  rcutorture: Add more diagnostics in rcu_barrier() test failure case
  torture: Flag console.log file to prevent holdovers from earlier runs
  torture: Add "-enable-kvm -soundhw pcspk" to qemu command line
  rcutorture: Handle different mpstat versions
  rcutorture: Check from beginning to end of grace period
  rcu: Remove redundant rcu_batches_completed() declaration
  rcutorture: Drop rcu_torture_completed() and friends
  rcu: Provide rcu_batches_completed_sched() for TINY_RCU
  rcutorture: Use unsigned for Reader Batch computations
  rcutorture: Make build-output parsing correctly flag RCU's warnings
  rcu: Make _batches_completed() functions return unsigned long
  rcutorture: Issue warnings on close calls due to Reader Batch blows
  documentation: Fix smp typo in memory-barriers.txt
  ...
parents 30d46827 f4902829

Documentation/RCU/stallwarn.txt

+15 −1
Original line number Diff line number Diff line
@@ -15,7 +15,7 @@ CONFIG_RCU_CPU_STALL_TIMEOUT 
	21 seconds.



	This configuration parameter may be changed at runtime via the

	/sys/module/rcutree/parameters/rcu_cpu_stall_timeout, however

	/sys/module/rcupdate/parameters/rcu_cpu_stall_timeout, however

	this parameter is checked only at the beginning of a cycle.

	So if you are 10 seconds into a 40-second stall, setting this

	sysfs parameter to (say) five will shorten the timeout for the
@@ -152,6 +152,15 @@ no non-lazy callbacks ("." is printed otherwise, as shown above) and 
"D" indicates that dyntick-idle processing is enabled ("." is printed

otherwise, for example, if disabled via the "nohz=" kernel boot parameter).



If the relevant grace-period kthread has been unable to run prior to

the stall warning, the following additional line is printed:



	rcu_preempt kthread starved for 2023 jiffies!



Starving the grace-period kthreads of CPU time can of course result in

RCU CPU stall warnings even when all CPUs and tasks have passed through

the required quiescent states.





Multiple Warnings From One Stall
@@ -187,6 +196,11 @@ o For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the 
	behavior, you might need to replace some of the cond_resched()

	calls with calls to cond_resched_rcu_qs().



o	Anything that prevents RCU's grace-period kthreads from running.

	This can result in the "All QSes seen" console-log message.

	This message will include information on when the kthread last

	ran and how often it should be expected to run.



o	A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might

	happen to preempt a low-priority task in the middle of an RCU

	read-side critical section.   This is especially damaging if

Documentation/RCU/trace.txt

+16 −16
Original line number Diff line number Diff line
@@ -56,14 +56,14 @@ rcuboost: 


The output of "cat rcu/rcu_preempt/rcudata" looks as follows:



  0!c=30455 g=30456 pq=1 qp=1 dt=126535/140000000000000/0 df=2002 of=4 ql=0/0 qs=N... b=10 ci=74572 nci=0 co=1131 ca=716

  1!c=30719 g=30720 pq=1 qp=0 dt=132007/140000000000000/0 df=1874 of=10 ql=0/0 qs=N... b=10 ci=123209 nci=0 co=685 ca=982

  2!c=30150 g=30151 pq=1 qp=1 dt=138537/140000000000000/0 df=1707 of=8 ql=0/0 qs=N... b=10 ci=80132 nci=0 co=1328 ca=1458

  3 c=31249 g=31250 pq=1 qp=0 dt=107255/140000000000000/0 df=1749 of=6 ql=0/450 qs=NRW. b=10 ci=151700 nci=0 co=509 ca=622

  4!c=29502 g=29503 pq=1 qp=1 dt=83647/140000000000000/0 df=965 of=5 ql=0/0 qs=N... b=10 ci=65643 nci=0 co=1373 ca=1521

  5 c=31201 g=31202 pq=1 qp=1 dt=70422/0/0 df=535 of=7 ql=0/0 qs=.... b=10 ci=58500 nci=0 co=764 ca=698

  6!c=30253 g=30254 pq=1 qp=1 dt=95363/140000000000000/0 df=780 of=5 ql=0/0 qs=N... b=10 ci=100607 nci=0 co=1414 ca=1353

  7 c=31178 g=31178 pq=1 qp=0 dt=91536/0/0 df=547 of=4 ql=0/0 qs=.... b=10 ci=109819 nci=0 co=1115 ca=969

  0!c=30455 g=30456 pq=1/0 qp=1 dt=126535/140000000000000/0 df=2002 of=4 ql=0/0 qs=N... b=10 ci=74572 nci=0 co=1131 ca=716

  1!c=30719 g=30720 pq=1/0 qp=0 dt=132007/140000000000000/0 df=1874 of=10 ql=0/0 qs=N... b=10 ci=123209 nci=0 co=685 ca=982

  2!c=30150 g=30151 pq=1/1 qp=1 dt=138537/140000000000000/0 df=1707 of=8 ql=0/0 qs=N... b=10 ci=80132 nci=0 co=1328 ca=1458

  3 c=31249 g=31250 pq=1/1 qp=0 dt=107255/140000000000000/0 df=1749 of=6 ql=0/450 qs=NRW. b=10 ci=151700 nci=0 co=509 ca=622

  4!c=29502 g=29503 pq=1/0 qp=1 dt=83647/140000000000000/0 df=965 of=5 ql=0/0 qs=N... b=10 ci=65643 nci=0 co=1373 ca=1521

  5 c=31201 g=31202 pq=1/0 qp=1 dt=70422/0/0 df=535 of=7 ql=0/0 qs=.... b=10 ci=58500 nci=0 co=764 ca=698

  6!c=30253 g=30254 pq=1/0 qp=1 dt=95363/140000000000000/0 df=780 of=5 ql=0/0 qs=N... b=10 ci=100607 nci=0 co=1414 ca=1353

  7 c=31178 g=31178 pq=1/0 qp=0 dt=91536/0/0 df=547 of=4 ql=0/0 qs=.... b=10 ci=109819 nci=0 co=1115 ca=969



This file has one line per CPU, or eight for this 8-CPU system.

The fields are as follows:
@@ -188,14 +188,14 @@ o "ca" is the number of RCU callbacks that have been adopted by this 
Kernels compiled with CONFIG_RCU_BOOST=y display the following from

/debug/rcu/rcu_preempt/rcudata:



  0!c=12865 g=12866 pq=1 qp=1 dt=83113/140000000000000/0 df=288 of=11 ql=0/0 qs=N... kt=0/O ktl=944 b=10 ci=60709 nci=0 co=748 ca=871

  1 c=14407 g=14408 pq=1 qp=0 dt=100679/140000000000000/0 df=378 of=7 ql=0/119 qs=NRW. kt=0/W ktl=9b6 b=10 ci=109740 nci=0 co=589 ca=485

  2 c=14407 g=14408 pq=1 qp=0 dt=105486/0/0 df=90 of=9 ql=0/89 qs=NRW. kt=0/W ktl=c0c b=10 ci=83113 nci=0 co=533 ca=490

  3 c=14407 g=14408 pq=1 qp=0 dt=107138/0/0 df=142 of=8 ql=0/188 qs=NRW. kt=0/W ktl=b96 b=10 ci=121114 nci=0 co=426 ca=290

  4 c=14405 g=14406 pq=1 qp=1 dt=50238/0/0 df=706 of=7 ql=0/0 qs=.... kt=0/W ktl=812 b=10 ci=34929 nci=0 co=643 ca=114

  5!c=14168 g=14169 pq=1 qp=0 dt=45465/140000000000000/0 df=161 of=11 ql=0/0 qs=N... kt=0/O ktl=b4d b=10 ci=47712 nci=0 co=677 ca=722

  6 c=14404 g=14405 pq=1 qp=0 dt=59454/0/0 df=94 of=6 ql=0/0 qs=.... kt=0/W ktl=e57 b=10 ci=55597 nci=0 co=701 ca=811

  7 c=14407 g=14408 pq=1 qp=1 dt=68850/0/0 df=31 of=8 ql=0/0 qs=.... kt=0/W ktl=14bd b=10 ci=77475 nci=0 co=508 ca=1042

  0!c=12865 g=12866 pq=1/0 qp=1 dt=83113/140000000000000/0 df=288 of=11 ql=0/0 qs=N... kt=0/O ktl=944 b=10 ci=60709 nci=0 co=748 ca=871

  1 c=14407 g=14408 pq=1/0 qp=0 dt=100679/140000000000000/0 df=378 of=7 ql=0/119 qs=NRW. kt=0/W ktl=9b6 b=10 ci=109740 nci=0 co=589 ca=485

  2 c=14407 g=14408 pq=1/0 qp=0 dt=105486/0/0 df=90 of=9 ql=0/89 qs=NRW. kt=0/W ktl=c0c b=10 ci=83113 nci=0 co=533 ca=490

  3 c=14407 g=14408 pq=1/0 qp=0 dt=107138/0/0 df=142 of=8 ql=0/188 qs=NRW. kt=0/W ktl=b96 b=10 ci=121114 nci=0 co=426 ca=290

  4 c=14405 g=14406 pq=1/0 qp=1 dt=50238/0/0 df=706 of=7 ql=0/0 qs=.... kt=0/W ktl=812 b=10 ci=34929 nci=0 co=643 ca=114

  5!c=14168 g=14169 pq=1/0 qp=0 dt=45465/140000000000000/0 df=161 of=11 ql=0/0 qs=N... kt=0/O ktl=b4d b=10 ci=47712 nci=0 co=677 ca=722

  6 c=14404 g=14405 pq=1/0 qp=0 dt=59454/0/0 df=94 of=6 ql=0/0 qs=.... kt=0/W ktl=e57 b=10 ci=55597 nci=0 co=701 ca=811

  7 c=14407 g=14408 pq=1/0 qp=1 dt=68850/0/0 df=31 of=8 ql=0/0 qs=.... kt=0/W ktl=14bd b=10 ci=77475 nci=0 co=508 ca=1042



This is similar to the output discussed above, but contains the following

additional fields:

Documentation/memory-barriers.txt

+45 −1
Original line number Diff line number Diff line
@@ -269,6 +269,50 @@ And there are a number of things that _must_ or _must_not_ be assumed: 
	STORE *(A + 4) = Y; STORE *A = X;

	STORE {*A, *(A + 4) } = {X, Y};



And there are anti-guarantees:



 (*) These guarantees do not apply to bitfields, because compilers often

     generate code to modify these using non-atomic read-modify-write

     sequences.  Do not attempt to use bitfields to synchronize parallel

     algorithms.



 (*) Even in cases where bitfields are protected by locks, all fields

     in a given bitfield must be protected by one lock.  If two fields

     in a given bitfield are protected by different locks, the compiler's

     non-atomic read-modify-write sequences can cause an update to one

     field to corrupt the value of an adjacent field.



 (*) These guarantees apply only to properly aligned and sized scalar

     variables.  "Properly sized" currently means variables that are

     the same size as "char", "short", "int" and "long".  "Properly

     aligned" means the natural alignment, thus no constraints for

     "char", two-byte alignment for "short", four-byte alignment for

     "int", and either four-byte or eight-byte alignment for "long",

     on 32-bit and 64-bit systems, respectively.  Note that these

     guarantees were introduced into the C11 standard, so beware when

     using older pre-C11 compilers (for example, gcc 4.6).  The portion

     of the standard containing this guarantee is Section 3.14, which

     defines "memory location" as follows:



     	memory location

		either an object of scalar type, or a maximal sequence

		of adjacent bit-fields all having nonzero width



		NOTE 1: Two threads of execution can update and access

		separate memory locations without interfering with

		each other.



		NOTE 2: A bit-field and an adjacent non-bit-field member

		are in separate memory locations. The same applies

		to two bit-fields, if one is declared inside a nested

		structure declaration and the other is not, or if the two

		are separated by a zero-length bit-field declaration,

		or if they are separated by a non-bit-field member

		declaration. It is not safe to concurrently update two

		bit-fields in the same structure if all members declared

		between them are also bit-fields, no matter what the

		sizes of those intervening bit-fields happen to be.





=========================

WHAT ARE MEMORY BARRIERS?
@@ -750,7 +794,7 @@ In summary: 
      However, they do -not- guarantee any other sort of ordering:

      Not prior loads against later loads, nor prior stores against

      later anything.  If you need these other forms of ordering,

      use smb_rmb(), smp_wmb(), or, in the case of prior stores and

      use smp_rmb(), smp_wmb(), or, in the case of prior stores and

      later loads, smp_mb().



  (*) If both legs of the "if" statement begin with identical stores

arch/arm/kvm/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ config KVM 
	select HAVE_KVM_CPU_RELAX_INTERCEPT

	select KVM_MMIO

	select KVM_ARM_HOST

	select SRCU

	depends on ARM_VIRT_EXT && ARM_LPAE

	---help---

	  Support hosting virtualized guest machines. You will also

arch/arm64/kvm/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ config KVM 
	select KVM_ARM_HOST

	select KVM_ARM_VGIC

	select KVM_ARM_TIMER

	select SRCU

	---help---

	  Support hosting virtualized guest machines.

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