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, 129 insertions, 0 deletions

diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
new file mode 100644
index 000000000..4a6574b67
--- /dev/null
+++ b/lib/strnlen_user.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/uaccess.h>
+#include <linux/mm.h>
+#include <linux/bitops.h>
+
+#include <asm/word-at-a-time.h>
+
+/*
+ * Do a strnlen, return length of string *with* final '\0'.
+ * 'count' is the user-supplied count, while 'max' is the
+ * address space maximum.
+ *
+ * Return 0 for exceptions (which includes hitting the address
+ * space maximum), or 'count+1' if hitting the user-supplied
+ * maximum count.
+ *
+ * NOTE! We can sometimes overshoot the user-supplied maximum
+ * if it fits in a aligned 'long'. The caller needs to check
+ * the return value against "> max".
+ */
+static __always_inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
+{
+	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
+	unsigned long align, res = 0;
+	unsigned long c;
+
+	/*
+	 * Do everything aligned. But that means that we
+	 * need to also expand the maximum..
+	 */
+	align = (sizeof(unsigned long) - 1) & (unsigned long)src;
+	src -= align;
+	max += align;
+
+	unsafe_get_user(c, (unsigned long __user *)src, efault);
+	c |= aligned_byte_mask(align);
+
+	for (;;) {
+		unsigned long data;
+		if (has_zero(c, &data, &constants)) {
+			data = prep_zero_mask(c, data, &constants);
+			data = create_zero_mask(data);
+			return res + find_zero(data) + 1 - align;
+		}
+		res += sizeof(unsigned long);
+		/* We already handled 'unsigned long' bytes. Did we do it all ? */
+		if (unlikely(max <= sizeof(unsigned long)))
+			break;
+		max -= sizeof(unsigned long);
+		unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
+	}
+	res -= align;
+
+	/*
+	 * Uhhuh. We hit 'max'. But was that the user-specified maximum
+	 * too? If so, return the marker for "too long".
+	 */
+	if (res >= count)
+		return count+1;
+
+	/*
+	 * Nope: we hit the address space limit, and we still had more
+	 * characters the caller would have wanted. That's 0.
+	 */
+efault:
+	return 0;
+}
+
+/**
+ * strnlen_user: - Get the size of a user string INCLUDING final NUL.
+ * @str: The string to measure.
+ * @count: Maximum count (including NUL character)
+ *
+ * Context: User context only. This function may sleep if pagefaults are
+ *          enabled.
+ *
+ * Get the size of a NUL-terminated string in user space.
+ *
+ * Returns the size of the string INCLUDING the terminating NUL.
+ * If the string is too long, returns a number larger than @count. User
+ * has to check the return value against "> count".
+ * On exception (or invalid count), returns 0.
+ *
+ * NOTE! You should basically never use this function. There is
+ * almost never any valid case for using the length of a user space
+ * string, since the string can be changed at any time by other
+ * threads. Use "strncpy_from_user()" instead to get a stable copy
+ * of the string.
+ */
+long strnlen_user(const char __user *str, long count)
+{
+	unsigned long max_addr, src_addr;
+
+	if (unlikely(count <= 0))
+		return 0;
+
+	if (can_do_masked_user_access()) {
+		long retval;
+
+		str = masked_user_read_access_begin(str);
+		retval = do_strnlen_user(str, count, count);
+		user_read_access_end();
+		return retval;
+	}
+
+	max_addr = TASK_SIZE_MAX;
+	src_addr = (unsigned long)untagged_addr(str);
+	if (likely(src_addr < max_addr)) {
+		unsigned long max = max_addr - src_addr;
+		long retval;
+
+		/*
+		 * Truncate 'max' to the user-specified limit, so that
+		 * we only have one limit we need to check in the loop
+		 */
+		if (max > count)
+			max = count;
+
+		if (user_read_access_begin(str, max)) {
+			retval = do_strnlen_user(str, count, max);
+			user_read_access_end();
+			return retval;
+		}
+	}
+	return 0;
+}
+EXPORT_SYMBOL(strnlen_user);