Merge tag 'docs-4.20' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "This is a fairly typical cycle for documentation. There's some welcome
  readability improvements for the formatted output, some LICENSES
  updates including the addition of the ISC license, the removal of the
  unloved and unmaintained 00-INDEX files, the deprecated APIs document
  from Kees, more MM docs from Mike Rapoport, and the usual pile of typo
  fixes and corrections"

* tag 'docs-4.20' of git://git.lwn.net/linux: (41 commits)
  docs: Fix typos in histogram.rst
  docs: Introduce deprecated APIs list
  kernel-doc: fix declaration type determination
  doc: fix a typo in adding-syscalls.rst
  docs/admin-guide: memory-hotplug: remove table of contents
  doc: printk-formats: Remove bogus kobject references for device nodes
  Documentation: preempt-locking: Use better example
  dm flakey: Document "error_writes" feature
  docs/completion.txt: Fix a couple of punctuation nits
  LICENSES: Add ISC license text
  LICENSES: Add note to CDDL-1.0 license that it should not be used
  docs/core-api: memory-hotplug: add some details about locking internals
  docs/core-api: rename memory-hotplug-notifier to memory-hotplug
  docs: improve readability for people with poorer eyesight
  yama: clarify ptrace_scope=2 in Yama documentation
  docs/vm: split memory hotplug notifier description to Documentation/core-api
  docs: move memory hotplug description into admin-guide/mm
  doc: Fix acronym "FEKEK" in ecryptfs
  docs: fix some broken documentation references
  iommu: Fix passthrough option documentation
  ...

7 files changed, 259 insertions, 5 deletions

diff --git a/Documentation/core-api/boot-time-mm.rst b/Documentation/core-api/boot-time-mm.rst
index 03cb1643f46f..6e12e89a03e0 100644
--- a/Documentation/core-api/boot-time-mm.rst
+++ b/Documentation/core-api/boot-time-mm.rst
@@ -76,7 +76,7 @@ These interfaces available only with bootmem, i.e when ``CONFIG_NO_BOOTMEM=n``
 
 .. kernel-doc:: include/linux/bootmem.h
 .. kernel-doc:: mm/bootmem.c
-   :nodocs:
+   :functions:
 
 Memblock specific API
 ---------------------
@@ -89,4 +89,4 @@ really happens under the hood.
 
 .. kernel-doc:: include/linux/memblock.h
 .. kernel-doc:: mm/memblock.c
-   :nodocs:
+   :functions:
diff --git a/Documentation/core-api/gfp_mask-from-fs-io.rst b/Documentation/core-api/gfp_mask-from-fs-io.rst
index e0df8f416582..e7c32a8de126 100644
--- a/Documentation/core-api/gfp_mask-from-fs-io.rst
+++ b/Documentation/core-api/gfp_mask-from-fs-io.rst
@@ -1,3 +1,5 @@
+.. _gfp_mask_from_fs_io:
+
 =================================
 GFP masks used from FS/IO context
 =================================
diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
index 26b735cefb93..29c790f571a5 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -27,10 +27,13 @@ Core utilities
    errseq
    printk-formats
    circular-buffers
+   memory-allocation
    mm-api
    gfp_mask-from-fs-io
    timekeeping
    boot-time-mm
+   memory-hotplug
+
 
 Interfaces for kernel debugging
 ===============================
diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
new file mode 100644
index 000000000000..f8bb9aa120c4
--- /dev/null
+++ b/Documentation/core-api/memory-allocation.rst
@@ -0,0 +1,122 @@
+=======================
+Memory Allocation Guide
+=======================
+
+Linux provides a variety of APIs for memory allocation. You can
+allocate small chunks using `kmalloc` or `kmem_cache_alloc` families,
+large virtually contiguous areas using `vmalloc` and its derivatives,
+or you can directly request pages from the page allocator with
+`alloc_pages`. It is also possible to use more specialized allocators,
+for instance `cma_alloc` or `zs_malloc`.
+
+Most of the memory allocation APIs use GFP flags to express how that
+memory should be allocated. The GFP acronym stands for "get free
+pages", the underlying memory allocation function.
+
+Diversity of the allocation APIs combined with the numerous GFP flags
+makes the question "How should I allocate memory?" not that easy to
+answer, although very likely you should use
+
+::
+
+  kzalloc(<size>, GFP_KERNEL);
+
+Of course there are cases when other allocation APIs and different GFP
+flags must be used.
+
+Get Free Page flags
+===================
+
+The GFP flags control the allocators behavior. They tell what memory
+zones can be used, how hard the allocator should try to find free
+memory, whether the memory can be accessed by the userspace etc. The
+:ref:`Documentation/core-api/mm-api.rst <mm-api-gfp-flags>` provides
+reference documentation for the GFP flags and their combinations and
+here we briefly outline their recommended usage:
+
+  * Most of the time ``GFP_KERNEL`` is what you need. Memory for the
+    kernel data structures, DMAable memory, inode cache, all these and
+    many other allocations types can use ``GFP_KERNEL``. Note, that
+    using ``GFP_KERNEL`` implies ``GFP_RECLAIM``, which means that
+    direct reclaim may be triggered under memory pressure; the calling
+    context must be allowed to sleep.
+  * If the allocation is performed from an atomic context, e.g interrupt
+    handler, use ``GFP_NOWAIT``. This flag prevents direct reclaim and
+    IO or filesystem operations. Consequently, under memory pressure
+    ``GFP_NOWAIT`` allocation is likely to fail. Allocations which
+    have a reasonable fallback should be using ``GFP_NOWARN``.
+  * If you think that accessing memory reserves is justified and the kernel
+    will be stressed unless allocation succeeds, you may use ``GFP_ATOMIC``.
+  * Untrusted allocations triggered from userspace should be a subject
+    of kmem accounting and must have ``__GFP_ACCOUNT`` bit set. There
+    is the handy ``GFP_KERNEL_ACCOUNT`` shortcut for ``GFP_KERNEL``
+    allocations that should be accounted.
+  * Userspace allocations should use either of the ``GFP_USER``,
+    ``GFP_HIGHUSER`` or ``GFP_HIGHUSER_MOVABLE`` flags. The longer
+    the flag name the less restrictive it is.
+
+    ``GFP_HIGHUSER_MOVABLE`` does not require that allocated memory
+    will be directly accessible by the kernel and implies that the
+    data is movable.
+
+    ``GFP_HIGHUSER`` means that the allocated memory is not movable,
+    but it is not required to be directly accessible by the kernel. An
+    example may be a hardware allocation that maps data directly into
+    userspace but has no addressing limitations.
+
+    ``GFP_USER`` means that the allocated memory is not movable and it
+    must be directly accessible by the kernel.
+
+You may notice that quite a few allocations in the existing code
+specify ``GFP_NOIO`` or ``GFP_NOFS``. Historically, they were used to
+prevent recursion deadlocks caused by direct memory reclaim calling
+back into the FS or IO paths and blocking on already held
+resources. Since 4.12 the preferred way to address this issue is to
+use new scope APIs described in
+:ref:`Documentation/core-api/gfp_mask-from-fs-io.rst <gfp_mask_from_fs_io>`.
+
+Other legacy GFP flags are ``GFP_DMA`` and ``GFP_DMA32``. They are
+used to ensure that the allocated memory is accessible by hardware
+with limited addressing capabilities. So unless you are writing a
+driver for a device with such restrictions, avoid using these flags.
+And even with hardware with restrictions it is preferable to use
+`dma_alloc*` APIs.
+
+Selecting memory allocator
+==========================
+
+The most straightforward way to allocate memory is to use a function
+from the :c:func:`kmalloc` family. And, to be on the safe size it's
+best to use routines that set memory to zero, like
+:c:func:`kzalloc`. If you need to allocate memory for an array, there
+are :c:func:`kmalloc_array` and :c:func:`kcalloc` helpers.
+
+The maximal size of a chunk that can be allocated with `kmalloc` is
+limited. The actual limit depends on the hardware and the kernel
+configuration, but it is a good practice to use `kmalloc` for objects
+smaller than page size.
+
+For large allocations you can use :c:func:`vmalloc` and
+:c:func:`vzalloc`, or directly request pages from the page
+allocator. The memory allocated by `vmalloc` and related functions is
+not physically contiguous.
+
+If you are not sure whether the allocation size is too large for
+`kmalloc`, it is possible to use :c:func:`kvmalloc` and its
+derivatives. It will try to allocate memory with `kmalloc` and if the
+allocation fails it will be retried with `vmalloc`. There are
+restrictions on which GFP flags can be used with `kvmalloc`; please
+see :c:func:`kvmalloc_node` reference documentation. Note that
+`kvmalloc` may return memory that is not physically contiguous.
+
+If you need to allocate many identical objects you can use the slab
+cache allocator. The cache should be set up with
+:c:func:`kmem_cache_create` before it can be used. Afterwards
+:c:func:`kmem_cache_alloc` and its convenience wrappers can allocate
+memory from that cache.
+
+When the allocated memory is no longer needed it must be freed. You
+can use :c:func:`kvfree` for the memory allocated with `kmalloc`,
+`vmalloc` and `kvmalloc`. The slab caches should be freed with
+:c:func:`kmem_cache_free`. And don't forget to destroy the cache with
+:c:func:`kmem_cache_destroy`.
diff --git a/Documentation/core-api/memory-hotplug.rst b/Documentation/core-api/memory-hotplug.rst
new file mode 100644
index 000000000000..de7467e48067
--- /dev/null
+++ b/Documentation/core-api/memory-hotplug.rst
@@ -0,0 +1,125 @@
+.. _memory_hotplug:
+
+==============
+Memory hotplug
+==============
+
+Memory hotplug event notifier
+=============================
+
+Hotplugging events are sent to a notification queue.
+
+There are six types of notification defined in ``include/linux/memory.h``:
+
+MEM_GOING_ONLINE
+  Generated before new memory becomes available in order to be able to
+  prepare subsystems to handle memory. The page allocator is still unable
+  to allocate from the new memory.
+
+MEM_CANCEL_ONLINE
+  Generated if MEM_GOING_ONLINE fails.
+
+MEM_ONLINE
+  Generated when memory has successfully brought online. The callback may
+  allocate pages from the new memory.
+
+MEM_GOING_OFFLINE
+  Generated to begin the process of offlining memory. Allocations are no
+  longer possible from the memory but some of the memory to be offlined
+  is still in use. The callback can be used to free memory known to a
+  subsystem from the indicated memory block.
+
+MEM_CANCEL_OFFLINE
+  Generated if MEM_GOING_OFFLINE fails. Memory is available again from
+  the memory block that we attempted to offline.
+
+MEM_OFFLINE
+  Generated after offlining memory is complete.
+
+A callback routine can be registered by calling::
+
+  hotplug_memory_notifier(callback_func, priority)
+
+Callback functions with higher values of priority are called before callback
+functions with lower values.
+
+A callback function must have the following prototype::
+
+  int callback_func(
+    struct notifier_block *self, unsigned long action, void *arg);
+
+The first argument of the callback function (self) is a pointer to the block
+of the notifier chain that points to the callback function itself.
+The second argument (action) is one of the event types described above.
+The third argument (arg) passes a pointer of struct memory_notify::
+
+	struct memory_notify {
+		unsigned long start_pfn;
+		unsigned long nr_pages;
+		int status_change_nid_normal;
+		int status_change_nid_high;
+		int status_change_nid;
+	}
+
+- start_pfn is start_pfn of online/offline memory.
+- nr_pages is # of pages of online/offline memory.
+- status_change_nid_normal is set node id when N_NORMAL_MEMORY of nodemask
+  is (will be) set/clear, if this is -1, then nodemask status is not changed.
+- status_change_nid_high is set node id when N_HIGH_MEMORY of nodemask
+  is (will be) set/clear, if this is -1, then nodemask status is not changed.
+- status_change_nid is set node id when N_MEMORY of nodemask is (will be)
+  set/clear. It means a new(memoryless) node gets new memory by online and a
+  node loses all memory. If this is -1, then nodemask status is not changed.
+
+  If status_changed_nid* >= 0, callback should create/discard structures for the
+  node if necessary.
+
+The callback routine shall return one of the values
+NOTIFY_DONE, NOTIFY_OK, NOTIFY_BAD, NOTIFY_STOP
+defined in ``include/linux/notifier.h``
+
+NOTIFY_DONE and NOTIFY_OK have no effect on the further processing.
+
+NOTIFY_BAD is used as response to the MEM_GOING_ONLINE, MEM_GOING_OFFLINE,
+MEM_ONLINE, or MEM_OFFLINE action to cancel hotplugging. It stops
+further processing of the notification queue.
+
+NOTIFY_STOP stops further processing of the notification queue.
+
+Locking Internals
+=================
+
+When adding/removing memory that uses memory block devices (i.e. ordinary RAM),
+the device_hotplug_lock should be held to:
+
+- synchronize against online/offline requests (e.g. via sysfs). This way, memory
+  block devices can only be accessed (.online/.state attributes) by user
+  space once memory has been fully added. And when removing memory, we
+  know nobody is in critical sections.
+- synchronize against CPU hotplug and similar (e.g. relevant for ACPI and PPC)
+
+Especially, there is a possible lock inversion that is avoided using
+device_hotplug_lock when adding memory and user space tries to online that
+memory faster than expected:
+
+- device_online() will first take the device_lock(), followed by
+  mem_hotplug_lock
+- add_memory_resource() will first take the mem_hotplug_lock, followed by
+  the device_lock() (while creating the devices, during bus_add_device()).
+
+As the device is visible to user space before taking the device_lock(), this
+can result in a lock inversion.
+
+onlining/offlining of memory should be done via device_online()/
+device_offline() - to make sure it is properly synchronized to actions
+via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type)
+
+When adding/removing/onlining/offlining memory or adding/removing
+heterogeneous/device memory, we should always hold the mem_hotplug_lock in
+write mode to serialise memory hotplug (e.g. access to global/zone
+variables).
+
+In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read
+mode allows for a quite efficient get_online_mems/put_online_mems
+implementation, so code accessing memory can protect from that memory
+vanishing.
diff --git a/Documentation/core-api/mm-api.rst b/Documentation/core-api/mm-api.rst
index 46ae3537fb12..5ce1ec1dd066 100644
--- a/Documentation/core-api/mm-api.rst
+++ b/Documentation/core-api/mm-api.rst
@@ -14,6 +14,8 @@ User Space Memory Access
 .. kernel-doc:: mm/util.c
    :functions: get_user_pages_fast
 
+.. _mm-api-gfp-flags:
+
 Memory Allocation Controls
 ==========================
 
diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index 25dc591cb110..86023c33906f 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -376,15 +376,15 @@ correctness of the format string and va_list arguments.
 
 Passed by reference.
 
-kobjects
---------
+Device tree nodes
+-----------------
 
 ::
 
 	%pOF[fnpPcCF]
 
 
-For printing kobject based structs (device nodes). Default behaviour is
+For printing device tree node structures. Default behaviour is
 equivalent to %pOFf.
 
 	- f - device node full_name