Merge tag 'core-rcu-2020-08-03' of git://git.kernel.org/pub/scm/linux…

…/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:

 - kfree_rcu updates

 - RCU tasks updates

 - Read-side scalability tests

 - SRCU updates

 - Torture-test updates

 - Documentation updates

 - Miscellaneous fixes

* tag 'core-rcu-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (109 commits)
  torture: Remove obsolete "cd $KVM"
  torture: Avoid duplicate specification of qemu command
  torture: Dump ftrace at shutdown only if requested
  torture: Add kvm-tranform.sh script for qemu-cmd files
  torture: Add more tracing crib notes to kvm.sh
  torture: Improve diagnostic for KCSAN-incapable compilers
  torture: Correctly summarize build-only runs
  torture: Pass --kmake-arg to all make invocations
  rcutorture: Check for unwatched readers
  torture: Abstract out console-log error detection
  torture: Add a stop-run capability
  torture: Create qemu-cmd in --buildonly runs
  rcu/rcutorture: Replace 0 with false
  torture: Add --allcpus argument to the kvm.sh script
  torture: Remove whitespace from identify_qemu_vcpus output
  rcutorture: NULL rcu_torture_current earlier in cleanup code
  rcutorture: Handle non-statistic bang-string error messages
  torture: Set configfile variable to current scenario
  rcutorture: Add races with task-exit processing
  locktorture: Use true and false to assign to bool variables
  ...

Documentation/RCU/Design/Requirements/Requirements.rst

@@ -2583,7 +2583,12 @@ not work to have these markers in the trampoline itself, because there
 would need to be instructions following ``rcu_read_unlock()``. Although
 ``synchronize_rcu()`` would guarantee that execution reached the
 ``rcu_read_unlock()``, it would not be able to guarantee that execution
-had completely left the trampoline.
+had completely left the trampoline. Worse yet, in some situations
+the trampoline's protection must extend a few instructions *prior* to
+execution reaching the trampoline.  For example, these few instructions
+might calculate the address of the trampoline, so that entering the
+trampoline would be pre-ordained a surprisingly long time before execution
+actually reached the trampoline itself.
 
 The solution, in the form of `Tasks
 RCU <https://lwn.net/Articles/607117/>`__, is to have implicit read-side

Documentation/RCU/checklist.txt → Documentation/RCU/checklist.rst

@@ -1,4 +1,8 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+================================
 Review Checklist for RCU Patches
+================================
 
 
 This document contains a checklist for producing and reviewing patches
@@ -411,18 +415,21 @@ over a rather long period of time, but improvements are always welcome!
 	__rcu sparse checks to validate your RCU code.	These can help
 	find problems as follows:
 
-	CONFIG_PROVE_LOCKING: check that accesses to RCU-protected data
+	CONFIG_PROVE_LOCKING:
+		check that accesses to RCU-protected data
 		structures are carried out under the proper RCU
 		read-side critical section, while holding the right
 		combination of locks, or whatever other conditions
 		are appropriate.
 
-	CONFIG_DEBUG_OBJECTS_RCU_HEAD: check that you don't pass the
+	CONFIG_DEBUG_OBJECTS_RCU_HEAD:
+		check that you don't pass the
 		same object to call_rcu() (or friends) before an RCU
 		grace period has elapsed since the last time that you
 		passed that same object to call_rcu() (or friends).
 
-	__rcu sparse checks: tag the pointer to the RCU-protected data
+	__rcu sparse checks:
+		tag the pointer to the RCU-protected data
 		structure with __rcu, and sparse will warn you if you
 		access that pointer without the services of one of the
 		variants of rcu_dereference().
@@ -442,8 +449,8 @@ over a rather long period of time, but improvements are always welcome!
 
 	You instead need to use one of the barrier functions:
 
-	o	call_rcu() -> rcu_barrier()
-	o	call_srcu() -> srcu_barrier()
+	-	call_rcu() -> rcu_barrier()
+	-	call_srcu() -> srcu_barrier()
 
 	However, these barrier functions are absolutely -not- guaranteed
 	to wait for a grace period.  In fact, if there are no call_rcu()

Documentation/RCU/index.rst

@@ -1,3 +1,5 @@
+.. SPDX-License-Identifier: GPL-2.0
+
 .. _rcu_concepts:
 
 ============
@@ -8,10 +10,17 @@ RCU concepts
    :maxdepth: 3
 
    arrayRCU
+   checklist
+   lockdep
+   lockdep-splat
    rcubarrier
    rcu_dereference
    whatisRCU
    rcu
+   rculist_nulls
+   rcuref
+   torture
+   stallwarn
    listRCU
    NMI-RCU
    UP

Documentation/RCU/lockdep-splat.txt → Documentation/RCU/lockdep-splat.rst

@@ -1,3 +1,9 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================
+Lockdep-RCU Splat
+=================
+
 Lockdep-RCU was added to the Linux kernel in early 2010
 (http://lwn.net/Articles/371986/).  This facility checks for some common
 misuses of the RCU API, most notably using one of the rcu_dereference()
@@ -12,55 +18,54 @@ overwriting or worse.  There can of course be false positives, this
 being the real world and all that.
 
 So let's look at an example RCU lockdep splat from 3.0-rc5, one that
-has long since been fixed:
-
-=============================
-WARNING: suspicious RCU usage
------------------------------
-block/cfq-iosched.c:2776 suspicious rcu_dereference_protected() usage!
-
-other info that might help us debug this:
-
-
-rcu_scheduler_active = 1, debug_locks = 0
-3 locks held by scsi_scan_6/1552:
- #0:  (&shost->scan_mutex){+.+.}, at: [<ffffffff8145efca>]
-scsi_scan_host_selected+0x5a/0x150
- #1:  (&eq->sysfs_lock){+.+.}, at: [<ffffffff812a5032>]
-elevator_exit+0x22/0x60
- #2:  (&(&q->__queue_lock)->rlock){-.-.}, at: [<ffffffff812b6233>]
-cfq_exit_queue+0x43/0x190
-
-stack backtrace:
-Pid: 1552, comm: scsi_scan_6 Not tainted 3.0.0-rc5 #17
-Call Trace:
- [<ffffffff810abb9b>] lockdep_rcu_dereference+0xbb/0xc0
- [<ffffffff812b6139>] __cfq_exit_single_io_context+0xe9/0x120
- [<ffffffff812b626c>] cfq_exit_queue+0x7c/0x190
- [<ffffffff812a5046>] elevator_exit+0x36/0x60
- [<ffffffff812a802a>] blk_cleanup_queue+0x4a/0x60
- [<ffffffff8145cc09>] scsi_free_queue+0x9/0x10
- [<ffffffff81460944>] __scsi_remove_device+0x84/0xd0
- [<ffffffff8145dca3>] scsi_probe_and_add_lun+0x353/0xb10
- [<ffffffff817da069>] ? error_exit+0x29/0xb0
- [<ffffffff817d98ed>] ? _raw_spin_unlock_irqrestore+0x3d/0x80
- [<ffffffff8145e722>] __scsi_scan_target+0x112/0x680
- [<ffffffff812c690d>] ? trace_hardirqs_off_thunk+0x3a/0x3c
- [<ffffffff817da069>] ? error_exit+0x29/0xb0
- [<ffffffff812bcc60>] ? kobject_del+0x40/0x40
- [<ffffffff8145ed16>] scsi_scan_channel+0x86/0xb0
- [<ffffffff8145f0b0>] scsi_scan_host_selected+0x140/0x150
- [<ffffffff8145f149>] do_scsi_scan_host+0x89/0x90
- [<ffffffff8145f170>] do_scan_async+0x20/0x160
- [<ffffffff8145f150>] ? do_scsi_scan_host+0x90/0x90
- [<ffffffff810975b6>] kthread+0xa6/0xb0
- [<ffffffff817db154>] kernel_thread_helper+0x4/0x10
- [<ffffffff81066430>] ? finish_task_switch+0x80/0x110
- [<ffffffff817d9c04>] ? retint_restore_args+0xe/0xe
- [<ffffffff81097510>] ? __kthread_init_worker+0x70/0x70
- [<ffffffff817db150>] ? gs_change+0xb/0xb
-
-Line 2776 of block/cfq-iosched.c in v3.0-rc5 is as follows:
+has long since been fixed::
+
+    =============================
+    WARNING: suspicious RCU usage
+    -----------------------------
+    block/cfq-iosched.c:2776 suspicious rcu_dereference_protected() usage!
+
+other info that might help us debug this::
+
+    rcu_scheduler_active = 1, debug_locks = 0
+    3 locks held by scsi_scan_6/1552:
+    #0:  (&shost->scan_mutex){+.+.}, at: [<ffffffff8145efca>]
+    scsi_scan_host_selected+0x5a/0x150
+    #1:  (&eq->sysfs_lock){+.+.}, at: [<ffffffff812a5032>]
+    elevator_exit+0x22/0x60
+    #2:  (&(&q->__queue_lock)->rlock){-.-.}, at: [<ffffffff812b6233>]
+    cfq_exit_queue+0x43/0x190
+
+    stack backtrace:
+    Pid: 1552, comm: scsi_scan_6 Not tainted 3.0.0-rc5 #17
+    Call Trace:
+    [<ffffffff810abb9b>] lockdep_rcu_dereference+0xbb/0xc0
+    [<ffffffff812b6139>] __cfq_exit_single_io_context+0xe9/0x120
+    [<ffffffff812b626c>] cfq_exit_queue+0x7c/0x190
+    [<ffffffff812a5046>] elevator_exit+0x36/0x60
+    [<ffffffff812a802a>] blk_cleanup_queue+0x4a/0x60
+    [<ffffffff8145cc09>] scsi_free_queue+0x9/0x10
+    [<ffffffff81460944>] __scsi_remove_device+0x84/0xd0
+    [<ffffffff8145dca3>] scsi_probe_and_add_lun+0x353/0xb10
+    [<ffffffff817da069>] ? error_exit+0x29/0xb0
+    [<ffffffff817d98ed>] ? _raw_spin_unlock_irqrestore+0x3d/0x80
+    [<ffffffff8145e722>] __scsi_scan_target+0x112/0x680
+    [<ffffffff812c690d>] ? trace_hardirqs_off_thunk+0x3a/0x3c
+    [<ffffffff817da069>] ? error_exit+0x29/0xb0
+    [<ffffffff812bcc60>] ? kobject_del+0x40/0x40
+    [<ffffffff8145ed16>] scsi_scan_channel+0x86/0xb0
+    [<ffffffff8145f0b0>] scsi_scan_host_selected+0x140/0x150
+    [<ffffffff8145f149>] do_scsi_scan_host+0x89/0x90
+    [<ffffffff8145f170>] do_scan_async+0x20/0x160
+    [<ffffffff8145f150>] ? do_scsi_scan_host+0x90/0x90
+    [<ffffffff810975b6>] kthread+0xa6/0xb0
+    [<ffffffff817db154>] kernel_thread_helper+0x4/0x10
+    [<ffffffff81066430>] ? finish_task_switch+0x80/0x110
+    [<ffffffff817d9c04>] ? retint_restore_args+0xe/0xe
+    [<ffffffff81097510>] ? __kthread_init_worker+0x70/0x70
+    [<ffffffff817db150>] ? gs_change+0xb/0xb
+
+Line 2776 of block/cfq-iosched.c in v3.0-rc5 is as follows::
 
 	if (rcu_dereference(ioc->ioc_data) == cic) {
 
@@ -70,7 +75,7 @@ case.  Instead, we hold three locks, one of which might be RCU related.
 And maybe that lock really does protect this reference.  If so, the fix
 is to inform RCU, perhaps by changing __cfq_exit_single_io_context() to
 take the struct request_queue "q" from cfq_exit_queue() as an argument,
-which would permit us to invoke rcu_dereference_protected as follows:
+which would permit us to invoke rcu_dereference_protected as follows::
 
 	if (rcu_dereference_protected(ioc->ioc_data,
 				      lockdep_is_held(&q->queue_lock)) == cic) {
@@ -85,7 +90,7 @@ On the other hand, perhaps we really do need an RCU read-side critical
 section.  In this case, the critical section must span the use of the
 return value from rcu_dereference(), or at least until there is some
 reference count incremented or some such.  One way to handle this is to
-add rcu_read_lock() and rcu_read_unlock() as follows:
+add rcu_read_lock() and rcu_read_unlock() as follows::
 
 	rcu_read_lock();
 	if (rcu_dereference(ioc->ioc_data) == cic) {
@@ -102,7 +107,7 @@ above lockdep-RCU splat.
 But in this particular case, we don't actually dereference the pointer
 returned from rcu_dereference().  Instead, that pointer is just compared
 to the cic pointer, which means that the rcu_dereference() can be replaced
-by rcu_access_pointer() as follows:
+by rcu_access_pointer() as follows::
 
 	if (rcu_access_pointer(ioc->ioc_data) == cic) {
 

Documentation/RCU/lockdep.txt → Documentation/RCU/lockdep.rst

@@ -1,4 +1,8 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================
 RCU and lockdep checking
+========================
 
 All flavors of RCU have lockdep checking available, so that lockdep is
 aware of when each task enters and leaves any flavor of RCU read-side
@@ -8,7 +12,7 @@ tracking to include RCU state, which can sometimes help when debugging
 deadlocks and the like.
 
 In addition, RCU provides the following primitives that check lockdep's
-state:
+state::
 
 	rcu_read_lock_held() for normal RCU.
 	rcu_read_lock_bh_held() for RCU-bh.
@@ -63,7 +67,7 @@ checking of rcu_dereference() primitives:
 The rcu_dereference_check() check expression can be any boolean
 expression, but would normally include a lockdep expression.  However,
 any boolean expression can be used.  For a moderately ornate example,
-consider the following:
+consider the following::
 
 	file = rcu_dereference_check(fdt->fd[fd],
 				     lockdep_is_held(&files->file_lock) ||
@@ -82,7 +86,7 @@ RCU read-side critical sections, in case (2) the ->file_lock prevents
 any change from taking place, and finally, in case (3) the current task
 is the only task accessing the file_struct, again preventing any change
 from taking place.  If the above statement was invoked only from updater
-code, it could instead be written as follows:
+code, it could instead be written as follows::
 
 	file = rcu_dereference_protected(fdt->fd[fd],
 					 lockdep_is_held(&files->file_lock) ||
@@ -105,7 +109,7 @@ false and they are called from outside any RCU read-side critical section.
 
 For example, the workqueue for_each_pwq() macro is intended to be used
 either within an RCU read-side critical section or with wq->mutex held.
-It is thus implemented as follows:
+It is thus implemented as follows::
 
 	#define for_each_pwq(pwq, wq)
 		list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,