Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull RCU changes from Paul E. McKenney:

 - Make kfree_rcu() use kfree_bulk() for added performance
 - RCU updates
 - Callback-overload handling updates
 - Tasks-RCU KCSAN and sparse updates
 - Locking torture test and RCU torture test updates
 - Documentation updates
 - Miscellaneous fixes

Signed-off-by: Ingo Molnar <[email protected]>

Author: Ingo Molnar

Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst

@@ -4,7 +4,7 @@ A Tour Through TREE_RCU's Grace-Period Memory Ordering
 
 August 8, 2017
 
-This article was contributed by Paul E. McKenney
+This article was contributed by Paul E. McKenney
 
 Introduction
 ============
@@ -48,7 +48,7 @@ Tree RCU Grace Period Memory Ordering Building Blocks
 
 The workhorse for RCU's grace-period memory ordering is the
 critical section for the ``rcu_node`` structure's
-``->lock``. These critical sections use helper functions for lock
+``->lock``. These critical sections use helper functions for lock
 acquisition, including ``raw_spin_lock_rcu_node()``,
 ``raw_spin_lock_irq_rcu_node()``, and ``raw_spin_lock_irqsave_rcu_node()``.
 Their lock-release counterparts are ``raw_spin_unlock_rcu_node()``,
@@ -102,9 +102,9 @@ lock-acquisition and lock-release functions::
    23   r3 = READ_ONCE(x);
    24 }
    25
-   26 WARN_ON(r1 == 0 && r2 == 0 && r3 == 0);
+   26 WARN_ON(r1 == 0 && r2 == 0 && r3 == 0);
 
-The ``WARN_ON()`` is evaluated at “the end of time”,
+The ``WARN_ON()`` is evaluated at "the end of time",
 after all changes have propagated throughout the system.
 Without the ``smp_mb__after_unlock_lock()`` provided by the
 acquisition functions, this ``WARN_ON()`` could trigger, for example

Documentation/RCU/listRCU.rst

@@ -11,8 +11,8 @@ must be long enough that any readers accessing the item being deleted have
 since dropped their references.  For example, an RCU-protected deletion
 from a linked list would first remove the item from the list, wait for
 a grace period to elapse, then free the element.  See the
-Documentation/RCU/listRCU.rst file for more information on using RCU with
-linked lists.
+:ref:`Documentation/RCU/listRCU.rst <list_rcu_doc>` for more information on
+using RCU with linked lists.
 
 Frequently Asked Questions
 --------------------------
@@ -50,7 +50,7 @@ Frequently Asked Questions
 - If I am running on a uniprocessor kernel, which can only do one
   thing at a time, why should I wait for a grace period?
 
-  See the Documentation/RCU/UP.rst file for more information.
+  See :ref:`Documentation/RCU/UP.rst <up_doc>` for more information.
 
 - How can I see where RCU is currently used in the Linux kernel?
 
@@ -68,18 +68,18 @@ Frequently Asked Questions
 
 - Why the name "RCU"?
 
-  "RCU" stands for "read-copy update".  The file Documentation/RCU/listRCU.rst
-  has more information on where this name came from, search for
-  "read-copy update" to find it.
+  "RCU" stands for "read-copy update".
+  :ref:`Documentation/RCU/listRCU.rst <list_rcu_doc>` has more information on where
+  this name came from, search for "read-copy update" to find it.
 
 - I hear that RCU is patented?  What is with that?
 
   Yes, it is.  There are several known patents related to RCU,
-  search for the string "Patent" in RTFP.txt to find them.
+  search for the string "Patent" in Documentation/RCU/RTFP.txt to find them.
   Of these, one was allowed to lapse by the assignee, and the
   others have been contributed to the Linux kernel under GPL.
   There are now also LGPL implementations of user-level RCU
-  available (http://liburcu.org/).
+  available (https://liburcu.org/).
 
 - I hear that RCU needs work in order to support realtime kernels?
 
@@ -88,5 +88,5 @@ Frequently Asked Questions
 
 - Where can I find more information on RCU?
 
-  See the RTFP.txt file in this directory.
+  See the Documentation/RCU/RTFP.txt file.
   Or point your browser at (http://www.rdrop.com/users/paulmck/RCU/).

Documentation/RCU/rcu.rst

@@ -124,9 +124,14 @@ using a dynamically allocated srcu_struct (hence "srcud-" rather than
 debugging.  The final "T" entry contains the totals of the counters.
 
 
-USAGE
+USAGE ON SPECIFIC KERNEL BUILDS
 
-The following script may be used to torture RCU:
+It is sometimes desirable to torture RCU on a specific kernel build,
+for example, when preparing to put that kernel build into production.
+In that case, the kernel should be built with CONFIG_RCU_TORTURE_TEST=m
+so that the test can be started using modprobe and terminated using rmmod.
+
+For example, the following script may be used to torture RCU:
 
 	#!/bin/sh
 
@@ -142,8 +147,136 @@ checked for such errors.  The "rmmod" command forces a "SUCCESS",
 two are self-explanatory, while the last indicates that while there
 were no RCU failures, CPU-hotplug problems were detected.
 
-However, the tools/testing/selftests/rcutorture/bin/kvm.sh script
-provides better automation, including automatic failure analysis.
-It assumes a qemu/kvm-enabled platform, and runs guest OSes out of initrd.
-See tools/testing/selftests/rcutorture/doc/initrd.txt for instructions
-on setting up such an initrd.
+
+USAGE ON MAINLINE KERNELS
+
+When using rcutorture to test changes to RCU itself, it is often
+necessary to build a number of kernels in order to test that change
+across a broad range of combinations of the relevant Kconfig options
+and of the relevant kernel boot parameters.  In this situation, use
+of modprobe and rmmod can be quite time-consuming and error-prone.
+
+Therefore, the tools/testing/selftests/rcutorture/bin/kvm.sh
+script is available for mainline testing for x86, arm64, and
+powerpc.  By default, it will run the series of tests specified by
+tools/testing/selftests/rcutorture/configs/rcu/CFLIST, with each test
+running for 30 minutes within a guest OS using a minimal userspace
+supplied by an automatically generated initrd.  After the tests are
+complete, the resulting build products and console output are analyzed
+for errors and the results of the runs are summarized.
+
+On larger systems, rcutorture testing can be accelerated by passing the
+--cpus argument to kvm.sh.  For example, on a 64-CPU system, "--cpus 43"
+would use up to 43 CPUs to run tests concurrently, which as of v5.4 would
+complete all the scenarios in two batches, reducing the time to complete
+from about eight hours to about one hour (not counting the time to build
+the sixteen kernels).  The "--dryrun sched" argument will not run tests,
+but rather tell you how the tests would be scheduled into batches.  This
+can be useful when working out how many CPUs to specify in the --cpus
+argument.
+
+Not all changes require that all scenarios be run.  For example, a change
+to Tree SRCU might run only the SRCU-N and SRCU-P scenarios using the
+--configs argument to kvm.sh as follows:  "--configs 'SRCU-N SRCU-P'".
+Large systems can run multiple copies of of the full set of scenarios,
+for example, a system with 448 hardware threads can run five instances
+of the full set concurrently.  To make this happen:
+
+	kvm.sh --cpus 448 --configs '5*CFLIST'
+
+Alternatively, such a system can run 56 concurrent instances of a single
+eight-CPU scenario:
+
+	kvm.sh --cpus 448 --configs '56*TREE04'
+
+Or 28 concurrent instances of each of two eight-CPU scenarios:
+
+	kvm.sh --cpus 448 --configs '28*TREE03 28*TREE04'
+
+Of course, each concurrent instance will use memory, which can be
+limited using the --memory argument, which defaults to 512M.  Small
+values for memory may require disabling the callback-flooding tests
+using the --bootargs parameter discussed below.
+
+Sometimes additional debugging is useful, and in such cases the --kconfig
+parameter to kvm.sh may be used, for example, "--kconfig 'CONFIG_KASAN=y'".
+
+Kernel boot arguments can also be supplied, for example, to control
+rcutorture's module parameters.  For example, to test a change to RCU's
+CPU stall-warning code, use "--bootargs 'rcutorture.stall_cpu=30'".
+This will of course result in the scripting reporting a failure, namely
+the resuling RCU CPU stall warning.  As noted above, reducing memory may
+require disabling rcutorture's callback-flooding tests:
+
+	kvm.sh --cpus 448 --configs '56*TREE04' --memory 128M \
+		--bootargs 'rcutorture.fwd_progress=0'
+
+Sometimes all that is needed is a full set of kernel builds.  This is
+what the --buildonly argument does.
+
+Finally, the --trust-make argument allows each kernel build to reuse what
+it can from the previous kernel build.
+
+There are additional more arcane arguments that are documented in the
+source code of the kvm.sh script.
+
+If a run contains failures, the number of buildtime and runtime failures
+is listed at the end of the kvm.sh output, which you really should redirect
+to a file.  The build products and console output of each run is kept in
+tools/testing/selftests/rcutorture/res in timestamped directories.  A
+given directory can be supplied to kvm-find-errors.sh in order to have
+it cycle you through summaries of errors and full error logs.  For example:
+
+	tools/testing/selftests/rcutorture/bin/kvm-find-errors.sh \
+		tools/testing/selftests/rcutorture/res/2020.01.20-15.54.23
+
+However, it is often more convenient to access the files directly.
+Files pertaining to all scenarios in a run reside in the top-level
+directory (2020.01.20-15.54.23 in the example above), while per-scenario
+files reside in a subdirectory named after the scenario (for example,
+"TREE04").  If a given scenario ran more than once (as in "--configs
+'56*TREE04'" above), the directories corresponding to the second and
+subsequent runs of that scenario include a sequence number, for example,
+"TREE04.2", "TREE04.3", and so on.
+
+The most frequently used file in the top-level directory is testid.txt.
+If the test ran in a git repository, then this file contains the commit
+that was tested and any uncommitted changes in diff format.
+
+The most frequently used files in each per-scenario-run directory are:
+
+.config: This file contains the Kconfig options.
+
+Make.out: This contains build output for a specific scenario.
+
+console.log: This contains the console output for a specific scenario.
+	This file may be examined once the kernel has booted, but
+	it might not exist if the build failed.
+
+vmlinux: This contains the kernel, which can be useful with tools like
+	objdump and gdb.
+
+A number of additional files are available, but are less frequently used.
+Many are intended for debugging of rcutorture itself or of its scripting.
+
+As of v5.4, a successful run with the default set of scenarios produces
+the following summary at the end of the run on a 12-CPU system:
+
+SRCU-N ------- 804233 GPs (148.932/s) [srcu: g10008272 f0x0 ]
+SRCU-P ------- 202320 GPs (37.4667/s) [srcud: g1809476 f0x0 ]
+SRCU-t ------- 1122086 GPs (207.794/s) [srcu: g0 f0x0 ]
+SRCU-u ------- 1111285 GPs (205.794/s) [srcud: g1 f0x0 ]
+TASKS01 ------- 19666 GPs (3.64185/s) [tasks: g0 f0x0 ]
+TASKS02 ------- 20541 GPs (3.80389/s) [tasks: g0 f0x0 ]
+TASKS03 ------- 19416 GPs (3.59556/s) [tasks: g0 f0x0 ]
+TINY01 ------- 836134 GPs (154.84/s) [rcu: g0 f0x0 ] n_max_cbs: 34198
+TINY02 ------- 850371 GPs (157.476/s) [rcu: g0 f0x0 ] n_max_cbs: 2631
+TREE01 ------- 162625 GPs (30.1157/s) [rcu: g1124169 f0x0 ]
+TREE02 ------- 333003 GPs (61.6672/s) [rcu: g2647753 f0x0 ] n_max_cbs: 35844
+TREE03 ------- 306623 GPs (56.782/s) [rcu: g2975325 f0x0 ] n_max_cbs: 1496497
+CPU count limited from 16 to 12
+TREE04 ------- 246149 GPs (45.5831/s) [rcu: g1695737 f0x0 ] n_max_cbs: 434961
+TREE05 ------- 314603 GPs (58.2598/s) [rcu: g2257741 f0x2 ] n_max_cbs: 193997
+TREE07 ------- 167347 GPs (30.9902/s) [rcu: g1079021 f0x0 ] n_max_cbs: 478732
+CPU count limited from 16 to 12
+TREE09 ------- 752238 GPs (139.303/s) [rcu: g13075057 f0x0 ] n_max_cbs: 99011

Documentation/RCU/torture.txt

@@ -3984,6 +3984,15 @@
 			Set threshold of queued RCU callbacks below which
 			batch limiting is re-enabled.
 
+	rcutree.qovld= [KNL]
+			Set threshold of queued RCU callbacks beyond which
+			RCU's force-quiescent-state scan will aggressively
+			enlist help from cond_resched() and sched IPIs to
+			help CPUs more quickly reach quiescent states.
+			Set to less than zero to make this be set based
+			on rcutree.qhimark at boot time and to zero to
+			disable more aggressive help enlistment.
+
 	rcutree.rcu_idle_gp_delay= [KNL]
 			Set wakeup interval for idle CPUs that have
 			RCU callbacks (RCU_FAST_NO_HZ=y).
@@ -4199,6 +4208,12 @@
 	rcupdate.rcu_cpu_stall_suppress= [KNL]
 			Suppress RCU CPU stall warning messages.
 
+	rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
+			Suppress RCU CPU stall warning messages and
+			rcutorture writer stall warnings that occur
+			during early boot, that is, during the time
+			before the init task is spawned.
+
 	rcupdate.rcu_cpu_stall_timeout= [KNL]
 			Set timeout for RCU CPU stall warning messages.
 
@@ -4871,6 +4886,10 @@
 			topology updates sent by the hypervisor to this
 			LPAR.
 
+	torture.disable_onoff_at_boot= [KNL]
+			Prevent the CPU-hotplug component of torturing
+			until after init has spawned.
+
 	tp720=		[HW,PS2]
 
 	tpm_suspend_pcr=[HW,TPM]

Documentation/admin-guide/kernel-parameters.txt

@@ -185,7 +185,7 @@ As a further example, consider this sequence of events:
 	===============	===============
 	{ A == 1, B == 2, C == 3, P == &A, Q == &C }
 	B = 4;		Q = P;
-	P = &B		D = *Q;
+	P = &B;		D = *Q;
 
 There is an obvious data dependency here, as the value loaded into D depends on
 the address retrieved from P by CPU 2.  At the end of the sequence, any of the
@@ -569,7 +569,7 @@ following sequence of events:
 	{ A == 1, B == 2, C == 3, P == &A, Q == &C }
 	B = 4;
 	<write barrier>
-	WRITE_ONCE(P, &B)
+	WRITE_ONCE(P, &B);
 			      Q = READ_ONCE(P);
 			      D = *Q;
 
@@ -1721,7 +1721,7 @@ of optimizations:
      and WRITE_ONCE() are more selective:  With READ_ONCE() and
      WRITE_ONCE(), the compiler need only forget the contents of the
      indicated memory locations, while with barrier() the compiler must
-     discard the value of all memory locations that it has currented
+     discard the value of all memory locations that it has currently
      cached in any machine registers.  Of course, the compiler must also
      respect the order in which the READ_ONCE()s and WRITE_ONCE()s occur,
      though the CPU of course need not do so.
@@ -1833,7 +1833,7 @@ Aside: In the case of data dependencies, the compiler would be expected
 to issue the loads in the correct order (eg. `a[b]` would have to load
 the value of b before loading a[b]), however there is no guarantee in
 the C specification that the compiler may not speculate the value of b
-(eg. is equal to 1) and load a before b (eg. tmp = a[1]; if (b != 1)
+(eg. is equal to 1) and load a[b] before b (eg. tmp = a[1]; if (b != 1)
 tmp = a[b]; ).  There is also the problem of a compiler reloading b after
 having loaded a[b], thus having a newer copy of b than a[b].  A consensus
 has not yet been reached about these problems, however the READ_ONCE()

Documentation/memory-barriers.txt

@@ -2489,7 +2489,7 @@ static int nfs_access_get_cached_rcu(struct inode *inode, const struct cred *cre
 	rcu_read_lock();
 	if (nfsi->cache_validity & NFS_INO_INVALID_ACCESS)
 		goto out;
-	lh = rcu_dereference(nfsi->access_cache_entry_lru.prev);
+	lh = rcu_dereference(list_tail_rcu(&nfsi->access_cache_entry_lru));
 	cache = list_entry(lh, struct nfs_access_entry, lru);
 	if (lh == &nfsi->access_cache_entry_lru ||
 	    cred_fscmp(cred, cache->cred) != 0)

fs/nfs/dir.c

@@ -60,9 +60,9 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
 #define __list_check_rcu(dummy, cond, extra...)				\
 	({								\
 	check_arg_count_one(extra);					\
-	RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),		\
+	RCU_LOCKDEP_WARN(!(cond) && !rcu_read_lock_any_held(),		\
 			 "RCU-list traversed in non-reader section!");	\
-	 })
+	})
 #else
 #define __list_check_rcu(dummy, cond, extra...)				\
 	({ check_arg_count_one(extra); })

include/linux/rculist.h

@@ -83,6 +83,7 @@ void rcu_scheduler_starting(void);
 static inline void rcu_scheduler_starting(void) { }
 #endif /* #else #ifndef CONFIG_SRCU */
 static inline void rcu_end_inkernel_boot(void) { }
+static inline bool rcu_inkernel_boot_has_ended(void) { return true; }
 static inline bool rcu_is_watching(void) { return true; }
 static inline void rcu_momentary_dyntick_idle(void) { }
 static inline void kfree_rcu_scheduler_running(void) { }

include/linux/rcutiny.h

@@ -54,6 +54,7 @@ void exit_rcu(void);
 void rcu_scheduler_starting(void);
 extern int rcu_scheduler_active __read_mostly;
 void rcu_end_inkernel_boot(void);
+bool rcu_inkernel_boot_has_ended(void);
 bool rcu_is_watching(void);
 #ifndef CONFIG_PREEMPTION
 void rcu_all_qs(void);