docs: admin-guide: merge sections for the kernel.modprobe sysctl

Documentation for the kernel.modprobe sysctl was added both by
commit 0317c53 ("docs: merge debugging-modules.txt into
sysctl/kernel.rst") and by commit 6e71582 ("docs: admin-guide:
document the kernel.modprobe sysctl"), resulting in the same sysctl
being documented in two places.  Merge these into one place.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20200414172430.230293-1-ebiggers@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/sysctl/kernel.rst

@@ -390,20 +390,33 @@ When ``kptr_restrict`` is set to 2, kernel pointers printed using
 modprobe
 ========
 
-This gives the full path of the modprobe command which the kernel will
-use to load modules. This can be used to debug module loading
-requests::
+The full path to the usermode helper for autoloading kernel modules,
+by default "/sbin/modprobe".  This binary is executed when the kernel
+requests a module.  For example, if userspace passes an unknown
+filesystem type to mount(), then the kernel will automatically request
+the corresponding filesystem module by executing this usermode helper.
+This usermode helper should insert the needed module into the kernel.
+
+This sysctl only affects module autoloading.  It has no effect on the
+ability to explicitly insert modules.
+
+This sysctl can be used to debug module loading requests::
 
     echo '#! /bin/sh' > /tmp/modprobe
     echo 'echo "$@" >> /tmp/modprobe.log' >> /tmp/modprobe
     echo 'exec /sbin/modprobe "$@"' >> /tmp/modprobe
     chmod a+x /tmp/modprobe
     echo /tmp/modprobe > /proc/sys/kernel/modprobe
 
-This only applies when the *kernel* is requesting that the module be
-loaded; it won't have any effect if the module is being loaded
-explicitly using ``modprobe`` from userspace.
+Alternatively, if this sysctl is set to the empty string, then module
+autoloading is completely disabled.  The kernel will not try to
+execute a usermode helper at all, nor will it call the
+kernel_module_request LSM hook.
 
+If CONFIG_STATIC_USERMODEHELPER=y is set in the kernel configuration,
+then the configured static usermode helper overrides this sysctl,
+except that the empty string is still accepted to completely disable
+module autoloading as described above.
 
 modules_disabled
 ================
@@ -446,28 +459,6 @@ Notes:
      successful IPC object allocation. If an IPC object allocation syscall
      fails, it is undefined if the value remains unmodified or is reset to -1.
 
-modprobe:
-=========
-
-The path to the usermode helper for autoloading kernel modules, by
-default "/sbin/modprobe".  This binary is executed when the kernel
-requests a module.  For example, if userspace passes an unknown
-filesystem type to mount(), then the kernel will automatically request
-the corresponding filesystem module by executing this usermode helper.
-This usermode helper should insert the needed module into the kernel.
-
-This sysctl only affects module autoloading.  It has no effect on the
-ability to explicitly insert modules.
-
-If this sysctl is set to the empty string, then module autoloading is
-completely disabled.  The kernel will not try to execute a usermode
-helper at all, nor will it call the kernel_module_request LSM hook.
-
-If CONFIG_STATIC_USERMODEHELPER=y is set in the kernel configuration,
-then the configured static usermode helper overrides this sysctl,
-except that the empty string is still accepted to completely disable
-module autoloading as described above.
-
 nmi_watchdog
 ============