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, 235 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-max6900.c b/drivers/rtc/rtc-max6900.c
new file mode 100644
index 000000000..8ef6d0fcd
--- /dev/null
+++ b/drivers/rtc/rtc-max6900.c
@@ -0,0 +1,235 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * rtc class driver for the Maxim MAX6900 chip
+ *
+ * Copyright (c) 2007 MontaVista, Software, Inc.
+ *
+ * Author: Dale Farnsworth <dale@farnsworth.org>
+ *
+ * based on previously existing rtc class drivers
+ */
+
+#include <linux/module.h>
+#include <linux/i2c.h>
+#include <linux/bcd.h>
+#include <linux/rtc.h>
+#include <linux/delay.h>
+
+/*
+ * register indices
+ */
+#define MAX6900_REG_SC			0	/* seconds      00-59 */
+#define MAX6900_REG_MN			1	/* minutes      00-59 */
+#define MAX6900_REG_HR			2	/* hours        00-23 */
+#define MAX6900_REG_DT			3	/* day of month 00-31 */
+#define MAX6900_REG_MO			4	/* month        01-12 */
+#define MAX6900_REG_DW			5	/* day of week   1-7  */
+#define MAX6900_REG_YR			6	/* year         00-99 */
+#define MAX6900_REG_CT			7	/* control */
+						/* register 8 is undocumented */
+#define MAX6900_REG_CENTURY		9	/* century */
+#define MAX6900_REG_LEN			10
+
+#define MAX6900_BURST_LEN		8	/* can burst r/w first 8 regs */
+
+#define MAX6900_REG_CT_WP		(1 << 7)	/* Write Protect */
+
+/*
+ * register read/write commands
+ */
+#define MAX6900_REG_CONTROL_WRITE	0x8e
+#define MAX6900_REG_CENTURY_WRITE	0x92
+#define MAX6900_REG_CENTURY_READ	0x93
+#define MAX6900_REG_RESERVED_READ	0x96
+#define MAX6900_REG_BURST_WRITE		0xbe
+#define MAX6900_REG_BURST_READ		0xbf
+
+#define MAX6900_IDLE_TIME_AFTER_WRITE	3	/* specification says 2.5 mS */
+
+static struct i2c_driver max6900_driver;
+
+static int max6900_i2c_read_regs(struct i2c_client *client, u8 *buf)
+{
+	u8 reg_burst_read[1] = { MAX6900_REG_BURST_READ };
+	u8 reg_century_read[1] = { MAX6900_REG_CENTURY_READ };
+	struct i2c_msg msgs[4] = {
+		{
+		 .addr = client->addr,
+		 .flags = 0,	/* write */
+		 .len = sizeof(reg_burst_read),
+		 .buf = reg_burst_read}
+		,
+		{
+		 .addr = client->addr,
+		 .flags = I2C_M_RD,
+		 .len = MAX6900_BURST_LEN,
+		 .buf = buf}
+		,
+		{
+		 .addr = client->addr,
+		 .flags = 0,	/* write */
+		 .len = sizeof(reg_century_read),
+		 .buf = reg_century_read}
+		,
+		{
+		 .addr = client->addr,
+		 .flags = I2C_M_RD,
+		 .len = sizeof(buf[MAX6900_REG_CENTURY]),
+		 .buf = &buf[MAX6900_REG_CENTURY]
+		 }
+	};
+	int rc;
+
+	rc = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
+	if (rc != ARRAY_SIZE(msgs)) {
+		dev_err(&client->dev, "%s: register read failed\n", __func__);
+		return -EIO;
+	}
+	return 0;
+}
+
+static int max6900_i2c_write_regs(struct i2c_client *client, u8 const *buf)
+{
+	u8 i2c_century_buf[1 + 1] = { MAX6900_REG_CENTURY_WRITE };
+	struct i2c_msg century_msgs[1] = {
+		{
+		 .addr = client->addr,
+		 .flags = 0,	/* write */
+		 .len = sizeof(i2c_century_buf),
+		 .buf = i2c_century_buf}
+	};
+	u8 i2c_burst_buf[MAX6900_BURST_LEN + 1] = { MAX6900_REG_BURST_WRITE };
+	struct i2c_msg burst_msgs[1] = {
+		{
+		 .addr = client->addr,
+		 .flags = 0,	/* write */
+		 .len = sizeof(i2c_burst_buf),
+		 .buf = i2c_burst_buf}
+	};
+	int rc;
+
+	/*
+	 * We have to make separate calls to i2c_transfer because of
+	 * the need to delay after each write to the chip.  Also,
+	 * we write the century byte first, since we set the write-protect
+	 * bit as part of the burst write.
+	 */
+	i2c_century_buf[1] = buf[MAX6900_REG_CENTURY];
+
+	rc = i2c_transfer(client->adapter, century_msgs,
+			  ARRAY_SIZE(century_msgs));
+	if (rc != ARRAY_SIZE(century_msgs))
+		goto write_failed;
+
+	msleep(MAX6900_IDLE_TIME_AFTER_WRITE);
+
+	memcpy(&i2c_burst_buf[1], buf, MAX6900_BURST_LEN);
+
+	rc = i2c_transfer(client->adapter, burst_msgs, ARRAY_SIZE(burst_msgs));
+	if (rc != ARRAY_SIZE(burst_msgs))
+		goto write_failed;
+	msleep(MAX6900_IDLE_TIME_AFTER_WRITE);
+
+	return 0;
+
+ write_failed:
+	dev_err(&client->dev, "%s: register write failed\n", __func__);
+	return -EIO;
+}
+
+static int max6900_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	int rc;
+	u8 regs[MAX6900_REG_LEN];
+
+	rc = max6900_i2c_read_regs(client, regs);
+	if (rc < 0)
+		return rc;
+
+	tm->tm_sec = bcd2bin(regs[MAX6900_REG_SC]);
+	tm->tm_min = bcd2bin(regs[MAX6900_REG_MN]);
+	tm->tm_hour = bcd2bin(regs[MAX6900_REG_HR] & 0x3f);
+	tm->tm_mday = bcd2bin(regs[MAX6900_REG_DT]);
+	tm->tm_mon = bcd2bin(regs[MAX6900_REG_MO]) - 1;
+	tm->tm_year = bcd2bin(regs[MAX6900_REG_YR]) +
+		      bcd2bin(regs[MAX6900_REG_CENTURY]) * 100 - 1900;
+	tm->tm_wday = bcd2bin(regs[MAX6900_REG_DW]);
+
+	return 0;
+}
+
+static int max6900_i2c_clear_write_protect(struct i2c_client *client)
+{
+	return i2c_smbus_write_byte_data(client, MAX6900_REG_CONTROL_WRITE, 0);
+}
+
+static int max6900_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	u8 regs[MAX6900_REG_LEN];
+	int rc;
+
+	rc = max6900_i2c_clear_write_protect(client);
+	if (rc < 0)
+		return rc;
+
+	regs[MAX6900_REG_SC] = bin2bcd(tm->tm_sec);
+	regs[MAX6900_REG_MN] = bin2bcd(tm->tm_min);
+	regs[MAX6900_REG_HR] = bin2bcd(tm->tm_hour);
+	regs[MAX6900_REG_DT] = bin2bcd(tm->tm_mday);
+	regs[MAX6900_REG_MO] = bin2bcd(tm->tm_mon + 1);
+	regs[MAX6900_REG_DW] = bin2bcd(tm->tm_wday);
+	regs[MAX6900_REG_YR] = bin2bcd(tm->tm_year % 100);
+	regs[MAX6900_REG_CENTURY] = bin2bcd((tm->tm_year + 1900) / 100);
+	/* set write protect */
+	regs[MAX6900_REG_CT] = MAX6900_REG_CT_WP;
+
+	rc = max6900_i2c_write_regs(client, regs);
+	if (rc < 0)
+		return rc;
+
+	return 0;
+}
+
+static const struct rtc_class_ops max6900_rtc_ops = {
+	.read_time = max6900_rtc_read_time,
+	.set_time = max6900_rtc_set_time,
+};
+
+static int max6900_probe(struct i2c_client *client)
+{
+	struct rtc_device *rtc;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
+		return -ENODEV;
+
+	rtc = devm_rtc_device_register(&client->dev, max6900_driver.driver.name,
+					&max6900_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	i2c_set_clientdata(client, rtc);
+
+	return 0;
+}
+
+static const struct i2c_device_id max6900_id[] = {
+	{ .name = "max6900" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, max6900_id);
+
+static struct i2c_driver max6900_driver = {
+	.driver = {
+		   .name = "rtc-max6900",
+		   },
+	.probe = max6900_probe,
+	.id_table = max6900_id,
+};
+
+module_i2c_driver(max6900_driver);
+
+MODULE_DESCRIPTION("Maxim MAX6900 RTC driver");
+MODULE_AUTHOR("Dale Farnsworth <dale@farnsworth.org>");
+MODULE_LICENSE("GPL");