From 9cc63f8bcd560c760d0b12e15bba8f81c86237cf Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: Fri, 14 Aug 2026 15:43:51 -0700
Subject: Merge branches 'expcb.2026.07.24a', 'misc.2026.07.30a',
 'rcu-tasks.2026.07.30a', 'srcu.2026.08.11a' and 'torture.2026.08.14a' into
 HEAD

Changes:

Make expedited grace periods expedite normal RCU callbacks

Miscellaneous fixes:
 * Improve diagnostic output with character task states.
 * Mark accesses to inform KCSAN of concurrency design.
 * Move from kmalloc() to kmalloc_obj().
 * Documentation updates.
 * Improve handling of RCU deferred quiescent states.
 * Clean up unused function arguments and structure fields.
 * Reduce show_rcu_gp_kthreads() stack space.

Tasks RCU updates:
 * Clean up after SRCU re-implementation of Tasks Trace RCU.
 * Mark accesses to inform KCSAN of concurrency design.
 * Add ->lazy_timer status to diagnostic output.
 * Remove an unnecessary memory barrier.
 * Fix a data race, courtesy of KCSAN.
 * Documentation updates.
 * Convert cond_resched_tasks_rcu_qs() from macro to static inline
   function.

SRCU updates:
 * Add Rust helpers for SRCU.
 * Avoid losing queued work at cleanup_srcu_struct() time.

Torture-test updates:
 * Preparation work for immediate RCU priority deboosting.
 * Test RCU readers from real interrupt handlers (as opposed to softirq).
 * Simplify code through use of cpumask_next_wrap().
 * Improve diagnostic output with character task states.
 * Add rcutorture.nwriters parameter to allow lightweight stall testing,
   and rcutorture.stall_only to make doing so easier.
 * Test an RCU Tasks Trace grace period implying an RCU grace period.
 * Make RCU Tasks Trace torturing track reader batches.
 * Fix a data race, courtesy of KCSAN.
 * Plug a shuffle_tmp_mask memory leak on kthread spawn failure.
---
 Documentation/admin-guide/device-mapper/delay.rst | 54 +++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 Documentation/admin-guide/device-mapper/delay.rst

(limited to 'Documentation/admin-guide/device-mapper/delay.rst')

diff --git a/Documentation/admin-guide/device-mapper/delay.rst b/Documentation/admin-guide/device-mapper/delay.rst
new file mode 100644
index 000000000..a1e673c0e
--- /dev/null
+++ b/Documentation/admin-guide/device-mapper/delay.rst
@@ -0,0 +1,54 @@
+========
+dm-delay
+========
+
+Device-Mapper's "delay" target delays reads and/or writes
+and/or flushes and optionally maps them to different devices.
+
+Arguments::
+
+    <device> <offset> <delay> [<write_device> <write_offset> <write_delay>
+			       [<flush_device> <flush_offset> <flush_delay>]]
+
+Table line has to either have 3, 6 or 9 arguments:
+
+3: apply offset and delay to read, write and flush operations on device
+
+6: apply offset and delay to device, also apply write_offset and write_delay
+   to write and flush operations on optionally different write_device with
+   optionally different sector offset
+
+9: same as 6 arguments plus define flush_offset and flush_delay explicitly
+   on/with optionally different flush_device/flush_offset.
+
+Offsets are specified in sectors.
+
+Delays are specified in milliseconds.
+
+
+Example scripts
+===============
+
+::
+	#!/bin/sh
+	#
+	# Create mapped device named "delayed" delaying read, write and flush operations for 500ms.
+	#
+	dmsetup create delayed --table  "0 `blockdev --getsz $1` delay $1 0 500"
+
+::
+	#!/bin/sh
+	#
+	# Create mapped device delaying write and flush operations for 400ms and
+	# splitting reads to device $1 but writes and flushes to different device $2
+	# to different offsets of 2048 and 4096 sectors respectively.
+	#
+	dmsetup create delayed --table "0 `blockdev --getsz $1` delay $1 2048 0 $2 4096 400"
+
+::
+	#!/bin/sh
+	#
+	# Create mapped device delaying reads for 50ms, writes for 100ms and flushes for 333ms
+	# onto the same backing device at offset 0 sectors.
+	#
+	dmsetup create delayed --table "0 `blockdev --getsz $1` delay $1 0 50 $2 0 100 $1 0 333"
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