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 HEADgrafted

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.

1 files changed, 177 insertions, 0 deletions

diff --git a/Documentation/admin-guide/ramoops.rst b/Documentation/admin-guide/ramoops.rst
new file mode 100644
index 000000000..2eabef312
--- /dev/null
+++ b/Documentation/admin-guide/ramoops.rst
@@ -0,0 +1,177 @@
+Ramoops oops/panic logger
+=========================
+
+Sergiu Iordache <sergiu@chromium.org>
+
+Updated: 10 Feb 2021
+
+Introduction
+------------
+
+Ramoops is an oops/panic logger that writes its logs to RAM before the system
+crashes. It works by logging oopses and panics in a circular buffer. Ramoops
+needs a system with persistent RAM so that the content of that area can
+survive after a restart.
+
+Ramoops concepts
+----------------
+
+Ramoops uses a predefined memory area to store the dump. The start and size
+and type of the memory area are set using three variables:
+
+  * ``mem_address`` for the start
+  * ``mem_size`` for the size. The memory size will be rounded down to a
+    power of two.
+  * ``mem_type`` to specify if the memory type (default is pgprot_writecombine).
+  * ``mem_name`` to specify a memory region defined by ``reserve_mem`` command
+    line parameter.
+
+Typically the default value of ``mem_type=0`` should be used as that sets the pstore
+mapping to pgprot_writecombine. Setting ``mem_type=1`` attempts to use
+``pgprot_noncached``, which only works on some platforms. This is because pstore
+depends on atomic operations. At least on ARM, pgprot_noncached causes the
+memory to be mapped strongly ordered, and atomic operations on strongly ordered
+memory are implementation defined, and won't work on many ARMs such as omaps.
+Setting ``mem_type=2`` attempts to treat the memory region as normal memory,
+which enables full cache on it. This can improve the performance.
+
+The memory area is divided into ``record_size`` chunks (also rounded down to
+power of two) and each kmesg dump writes a ``record_size`` chunk of
+information.
+
+Limiting which kinds of kmsg dumps are stored can be controlled via
+the ``max_reason`` value, as defined in include/linux/kmsg_dump.h's
+``enum kmsg_dump_reason``. For example, to store both Oopses and Panics,
+``max_reason`` should be set to 2 (KMSG_DUMP_OOPS), to store only Panics
+``max_reason`` should be set to 1 (KMSG_DUMP_PANIC). Setting this to 0
+(KMSG_DUMP_UNDEF), means the reason filtering will be controlled by the
+``printk.always_kmsg_dump`` boot param: if unset, it'll be KMSG_DUMP_OOPS,
+otherwise KMSG_DUMP_MAX.
+
+The module uses a counter to record multiple dumps but the counter gets reset
+on restart (i.e. new dumps after the restart will overwrite old ones).
+
+Ramoops also supports software ECC protection of persistent memory regions.
+This might be useful when a hardware reset was used to bring the machine back
+to life (i.e. a watchdog triggered). In such cases, RAM may be somewhat
+corrupt, but usually it is restorable.
+
+Setting the parameters
+----------------------
+
+Setting the ramoops parameters can be done in several different manners:
+
+ A. Use the module parameters (which have the names of the variables described
+ as before). For quick debugging, you can also reserve parts of memory during
+ boot and then use the reserved memory for ramoops. For example, assuming a
+ machine with > 128 MB of memory, the following kernel command line will tell
+ the kernel to use only the first 128 MB of memory, and place ECC-protected
+ ramoops region at 128 MB boundary::
+
+	mem=128M ramoops.mem_address=0x8000000 ramoops.ecc=1
+
+ B. Use Device Tree bindings, as described in
+ ``Documentation/devicetree/bindings/reserved-memory/ramoops.yaml``.
+ For example::
+
+	reserved-memory {
+		#address-cells = <2>;
+		#size-cells = <2>;
+		ranges;
+
+		ramoops@8f000000 {
+			compatible = "ramoops";
+			reg = <0 0x8f000000 0 0x100000>;
+			record-size = <0x4000>;
+			console-size = <0x4000>;
+		};
+	};
+
+ C. Use a platform device and set the platform data. The parameters can then
+ be set through that platform data. An example of doing that is:
+
+ .. code-block:: c
+
+  #include <linux/pstore_ram.h>
+  [...]
+
+  static struct ramoops_platform_data ramoops_data = {
+        .mem_size               = <...>,
+        .mem_address            = <...>,
+        .mem_type               = <...>,
+        .record_size            = <...>,
+        .max_reason             = <...>,
+        .ecc                    = <...>,
+  };
+
+  static struct platform_device ramoops_dev = {
+        .name = "ramoops",
+        .dev = {
+                .platform_data = &ramoops_data,
+        },
+  };
+
+  [... inside a function ...]
+  int ret;
+
+  ret = platform_device_register(&ramoops_dev);
+  if (ret) {
+	printk(KERN_ERR "unable to register platform device\n");
+	return ret;
+  }
+
+ D. Using a region of memory reserved via ``reserve_mem`` command line
+    parameter. The address and size will be defined by the ``reserve_mem``
+    parameter. Note, that ``reserve_mem`` may not always allocate memory
+    in the same location, and cannot be relied upon. Testing will need
+    to be done, and it may not work on every machine, nor every kernel.
+    Consider this a "best effort" approach. The ``reserve_mem`` option
+    takes a size, alignment and name as arguments. The name is used
+    to map the memory to a label that can be retrieved by ramoops.
+
+	reserve_mem=2M:4096:oops  ramoops.mem_name=oops
+
+You can specify either RAM memory or peripheral devices' memory. However, when
+specifying RAM, be sure to reserve the memory by issuing memblock_reserve()
+very early in the architecture code, e.g.::
+
+	#include <linux/memblock.h>
+
+	memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size);
+
+Dump format
+-----------
+
+The data dump begins with a header, currently defined as ``====`` followed by a
+timestamp and a new line. The dump then continues with the actual data.
+
+Reading the data
+----------------
+
+The dump data can be read from the pstore filesystem. The format for these
+files is ``dmesg-ramoops-N``, where N is the record number in memory. To delete
+a stored record from RAM, simply unlink the respective pstore file.
+
+Persistent function tracing
+---------------------------
+
+Persistent function tracing might be useful for debugging software or hardware
+related hangs. The functions call chain log is stored in a ``ftrace-ramoops``
+file. Here is an example of usage::
+
+ # mount -t debugfs debugfs /sys/kernel/debug/
+ # echo 1 > /sys/kernel/debug/pstore/record_ftrace
+ # reboot -f
+ [...]
+ # mount -t pstore pstore /mnt/
+ # tail /mnt/ftrace-ramoops
+ 0 ffffffff8101ea64  ffffffff8101bcda  native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0
+ 0 ffffffff8101ea44  ffffffff8101bcf6  native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0
+ 0 ffffffff81020084  ffffffff8101a4b5  hpet_disable <- native_machine_shutdown+0x75/0x90
+ 0 ffffffff81005f94  ffffffff8101a4bb  iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90
+ 0 ffffffff8101a6a1  ffffffff8101a437  native_machine_emergency_restart <- native_machine_restart+0x37/0x40
+ 0 ffffffff811f9876  ffffffff8101a73a  acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0
+ 0 ffffffff8101a514  ffffffff8101a772  mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0
+ 0 ffffffff811d9c54  ffffffff8101a7a0  __const_udelay <- native_machine_emergency_restart+0x110/0x1e0
+ 0 ffffffff811d9c34  ffffffff811d9c80  __delay <- __const_udelay+0x30/0x40
+ 0 ffffffff811d9d14  ffffffff811d9c3f  delay_tsc <- __delay+0xf/0x20