Subject: [Saphira] Linux 7.3: run kthreads with init fs context (2.4.4 port)

Saphira-Port-By: Muse Spark 1.3 Contributor for AKADATA LIMITED
(Andrew Smalley, Director)
Note: The API moved; the data must not. Re-derived hunk by hunk
for 2.4.4 and proven by boot, not by inspection.

Ports robn/zfs@e8a0a6cd4ed3 onto OpenZFS 2.4.4 (see recipe comments for the rebase notes).

--- a/include/os/linux/Makefile.am
+++ b/include/os/linux/Makefile.am
@@ -6,6 +6,7 @@
 	%D%/kernel/linux/compiler_compat.h \
 	%D%/kernel/linux/dcache_compat.h \
 	%D%/kernel/linux/kmap_compat.h \
+	%D%/kernel/linux/kthread_compat.h \
 	%D%/kernel/linux/mm_compat.h \
 	%D%/kernel/linux/mod_compat.h \
 	%D%/kernel/linux/page_compat.h \
--- a/module/os/linux/spl/spl-taskq.c
+++ b/module/os/linux/spl/spl-taskq.c
@@ -38,6 +38,7 @@
 #include <sys/kstat.h>
 #include <linux/cpuhotplug.h>
 #include <linux/mod_compat.h>
+#include <linux/kthread_compat.h>
 
 /* Linux 6.2 renamed timer_delete_sync(); point it at its old name for those. */
 #ifndef HAVE_TIMER_DELETE_SYNC
@@ -1107,7 +1108,8 @@
 			DTRACE_PROBE1(taskq_ent__start, taskq_ent_t *, t);
 
 			/* Perform the requested task */
-			t->tqent_func(t->tqent_arg);
+			scoped_with_init_fs()
+			    t->tqent_func(t->tqent_arg);
 
 			DTRACE_PROBE1(taskq_ent__finish, taskq_ent_t *, t);
 
--- a/module/os/linux/spl/spl-thread.c
+++ b/module/os/linux/spl/spl-thread.c
@@ -29,6 +29,7 @@
 #include <sys/tsd.h>
 #include <sys/string.h>
 #include <sys/misc.h>
+#include <linux/kthread_compat.h>
 
 /*
  * Thread interfaces
@@ -59,8 +60,10 @@
 	kmem_free(tp->tp_name, tp->tp_name_size);
 	kmem_free(tp, sizeof (thread_priv_t));
 
-	if (func)
-		func(args);
+	if (func) {
+		scoped_with_init_fs()
+		    func(args);
+	}
 
 	return (0);
 }
--- /dev/null
+++ b/include/os/linux/kernel/linux/kthread_compat.h
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: CDDL-1.0
+/*
+ * This file and its contents are supplied under the terms of the
+ * Common Development and Distribution License ("CDDL"), version 1.0.
+ * You may only use this file in accordance with the terms of version
+ * 1.0 of the CDDL.
+ *
+ * A full copy of the text of the CDDL should have accompanied this
+ * source.  A copy of the CDDL is also available via the Internet at
+ * https://opensource.org/license/CDDL-1.0.
+ */
+
+/*
+ * Copyright (c) 2026, TrueNAS.
+ */
+
+#ifndef _ZFS_KTHREAD_COMPAT_H
+#define	_ZFS_KTHREAD_COMPAT_H
+
+#include <linux/fs_struct.h>
+
+/*
+ * Linux 7.3 change. Kernel-internal threads no longer have access to the
+ * filesystem by default. Callers that need it should wrap the necessary code
+ * in `scoped_with_init_fs()`, which will make the filesystem availble until
+ * end of scope.
+ *
+ * For older kernels that do not provide this macro, we define it to be a
+ * no-op.
+ */
+#ifndef scoped_with_init_fs
+#define	scoped_with_init_fs()	if (1)
+#endif
+
+#endif