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

Pull RCU updates from Ingo Molnar:
 "This cycles's RCU changes include:

   - a couple of straggling RCU flavor consolidation updates

   - SRCU updates

   - RCU CPU stall-warning updates

   - torture-test updates

   - an LKMM commit adding support for synchronize_srcu_expedited()

   - documentation updates

   - miscellaneous fixes"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (57 commits)
  net/ipv4/netfilter: Update comment from call_rcu_bh() to call_rcu()
  tools/memory-model: Add support for synchronize_srcu_expedited()
  doc/kprobes: Update obsolete RCU update functions
  torture: Suppress false-positive CONFIG_INITRAMFS_SOURCE complaint
  locktorture: NULL cxt.lwsa and cxt.lrsa to allow bad-arg detection
  rcuperf: Fix cleanup path for invalid perf_type strings
  rcutorture: Fix cleanup path for invalid torture_type strings
  rcutorture: Fix expected forward progress duration in OOM notifier
  rcutorture: Remove ->ext_irq_conflict field
  rcutorture: Make rcutorture_extend_mask() comment match the code
  tools/.../rcutorture: Convert to SPDX license identifier
  torture: Don't try to offline the last CPU
  rcu: Fix nohz status in stall warning
  rcu: Move forward-progress checkers into tree_stall.h
  rcu: Move irq-disabled stall-warning checking to tree_stall.h
  rcu: Organize functions in tree_stall.h
  rcu: Move FAST_NO_HZ stall-warning code to tree_stall.h
  rcu: Inline RCU stall-warning info helper functions
  rcu: Move rcu_print_task_exp_stall() to tree_exp.h
  rcu: Inline RCU task stall-warning helper functions
  ...

1 files changed, 29 insertions, 4 deletions

diff --git a/tools/memory-model/README b/tools/memory-model/README
index 0f2c366518c6..2b87f3971548 100644
--- a/tools/memory-model/README
+++ b/tools/memory-model/README
@@ -20,13 +20,17 @@ that litmus test to be exercised within the Linux kernel.
 REQUIREMENTS
 ============
 
-Version 7.49 of the "herd7" and "klitmus7" tools must be downloaded
-separately:
+Version 7.52 or higher of the "herd7" and "klitmus7" tools must be
+downloaded separately:
 
   https://github.com/herd/herdtools7
 
 See "herdtools7/INSTALL.md" for installation instructions.
 
+Note that although these tools usually provide backwards compatibility,
+this is not absolutely guaranteed.  Therefore, if a later version does
+not work, please try using the exact version called out above.
+
 
 ==================
 BASIC USAGE: HERD7
@@ -221,8 +225,29 @@ The Linux-kernel memory model has the following limitations:
 		additional call_rcu() process to the site of the
 		emulated rcu-barrier().
 
-	e.	Sleepable RCU (SRCU) is not modeled.  It can be
-		emulated, but perhaps not simply.
+	e.	Although sleepable RCU (SRCU) is now modeled, there
+		are some subtle differences between its semantics and
+		those in the Linux kernel.  For example, the kernel
+		might interpret the following sequence as two partially
+		overlapping SRCU read-side critical sections:
+
+			 1  r1 = srcu_read_lock(&my_srcu);
+			 2  do_something_1();
+			 3  r2 = srcu_read_lock(&my_srcu);
+			 4  do_something_2();
+			 5  srcu_read_unlock(&my_srcu, r1);
+			 6  do_something_3();
+			 7  srcu_read_unlock(&my_srcu, r2);
+
+		In contrast, LKMM will interpret this as a nested pair of
+		SRCU read-side critical sections, with the outer critical
+		section spanning lines 1-7 and the inner critical section
+		spanning lines 3-5.
+
+		This difference would be more of a concern had anyone
+		identified a reasonable use case for partially overlapping
+		SRCU read-side critical sections.  For more information,
+		please see: https://paulmck.livejournal.com/40593.html
 
 	f.	Reader-writer locking is not modeled.  It can be
 		emulated in litmus tests using atomic read-modify-write