Set md_mod parameter legacy_async_del_gendisk only when the running kernel provides it

config.yaml

@@ -0,0 +1,23 @@
+actions:
+  - delete_line:
+    - target: "spec"
+      lines:
+        - "Patch202:    mdadm-get-rhel-version.patch"
+
+  - delete_files:
+    - file_name: "mdadm-get-rhel-version.patch"
+
+  - modify_release:
+    - suffix: ".alma.1"
+      enabled: true
+
+  - changelog_entry:
+    - name: "Andrew Lukoshko"
+      email: "alukoshko@almalinux.org"
+      line:
+        - "Set md_mod parameter legacy_async_del_gendisk only when the running kernel provides it"
+
+  - add_files:
+    - type: "patch"
+      name: "mdadm-get-MD_MOD_ASYNC_DEL_GENDISK.patch"
+      number: 202

files/mdadm-get-MD_MOD_ASYNC_DEL_GENDISK.patch

@@ -0,0 +1,72 @@
+Subject: Set legacy_async_del_gendisk only when the kernel supports it
+
+0042-mdadm-Create-array-with-sync-del-gendisk-mode.patch switches mdadm to
+the sync del_gendisk mode by writing N to the md_mod parameter
+legacy_async_del_gendisk. Upstream gates this on get_linux_version() >=
+6018000, which never matches a RHEL 9 kernel (5.14.0), and the RHEL patch
+mdadm-get-rhel-version.patch replaced it with a check for the z-stream
+number of the running kernel (>= 28), assuming kernel-5.14.0-611.28.1.el9_7
+or newer.
+
+Both variants are wrong for AlmaLinux 9:
+
+- the z-stream number is only comparable within a single minor release, so
+  9.6 kernels (5.14.0-570.x) and 9.8 kernels (5.14.0-6xx.y, y restarting
+  from a low number) are misdetected;
+- when the check passes but the running kernel does not provide the
+  parameter, set_md_mod_parameter() fails and init_md_mod() returns false,
+  which makes create_mddev() fail, i.e. arrays can't be created or
+  assembled at all.
+
+The parameter is added by kernel commit 25db5f284fb8 ("md: add
+legacy_async_del_gendisk mod"), which comes together with 9e59d609763f
+("md: call del_gendisk in control path"). Its presence in sysfs is
+therefore the exact condition mdadm needs, and it works for every kernel
+regardless of upstream or downstream versioning. If the parameter is not
+there, the kernel has the old async-only behaviour and nothing has to be
+set.
+
+--- a/util.c
++++ b/util.c
+@@ -2580,6 +2580,21 @@ bool set_md_mod_parameter(const char *name, const char *value)
+ 	return ret;
+ }
+ 
++/*
++ * Check if md_mod parameter is supported by the running kernel
++ * @name: name of the parameter
++ *
++ * Return: true if /sys/module/md_mod/parameters/<name> exists, false if not
++ */
++static bool md_mod_parameter_exists(const char *name)
++{
++	char path[256];
++
++	snprintf(path, sizeof(path), "/sys/module/md_mod/parameters/%s", name);
++
++	return access(path, F_OK) == 0;
++}
++
+ /* Init kernel md_mod and parameters here if needed */
+ bool init_md_mod(void)
+ {
+@@ -2624,10 +2639,16 @@ bool init_md_mod(void)
+ 	 * update mdadm and update to new kernel, they can't assemble array
+ 	 * anymore. So kernel adds a kernel parameter legacy_async_del_gendisk
+ 	 * and uses async as default.
+-	 * We'll use sync mode since 6.18 rather than async mode. So in future
+-	 * the kernel parameter will be removed.
++	 * We'll use sync mode rather than async mode. So in future the kernel
++	 * parameter will be removed.
++	 *
++	 * The kernel version can't be used to decide whether the parameter is
++	 * supported, because the two commits mentioned above are backported to
++	 * various downstream kernels which keep their own versioning. Check
++	 * sysfs to know if the running kernel provides the parameter and only
++	 * set it then, otherwise keep the kernel default.
+ 	 */
+-	if (get_linux_version() >= 6018000)
++	if (md_mod_parameter_exists(MD_MOD_ASYNC_DEL_GENDISK))
+ 		ret = set_md_mod_parameter(MD_MOD_ASYNC_DEL_GENDISK, "N");
+ 
+ 	return ret;