[merged mm-stable] documentation-mm-add-details-about-kmap_local_page-and-preemption.patch removed from -mm tree

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The quilt patch titled
     Subject: Documentation/mm: add details about kmap_local_page() and preemption
has been removed from the -mm tree.  Its filename was
     documentation-mm-add-details-about-kmap_local_page-and-preemption.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Fabio M. De Francesco" <fmdefrancesco@xxxxxxxxx>
Subject: Documentation/mm: add details about kmap_local_page() and preemption
Date: Thu, 28 Jul 2022 17:48:44 +0200

What happens if a thread is preempted after mapping pages with
kmap_local_page() was questioned recently.[1]

Commit f3ba3c710ac5 ("mm/highmem: Provide kmap_local*") from Thomas
Gleixner explains clearly that on context switch, the maps of an outgoing
task are removed and the map of the incoming task are restored and that
kmap_local_page() can be invoked from both preemptible and atomic
contexts.[2]

Therefore, for the purpose to make it clearer that users can call
kmap_local_page() from contexts that allow preemption, rework a couple of
sentences and add further information in highmem.rst.

[1] https://lore.kernel.org/lkml/5303077.Sb9uPGUboI@opensuse/
[2] https://lore.kernel.org/all/20201118204007.468533059@xxxxxxxxxxxxx/

Link: https://lkml.kernel.org/r/20220728154844.10874-8-fmdefrancesco@xxxxxxxxx
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx>
Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Peter Collingbourne <pcc@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 Documentation/mm/highmem.rst |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

--- a/Documentation/mm/highmem.rst~documentation-mm-add-details-about-kmap_local_page-and-preemption
+++ a/Documentation/mm/highmem.rst
@@ -60,14 +60,19 @@ list shows them in order of preference o
   This function should be preferred, where feasible, over all the others.
 
   These mappings are thread-local and CPU-local, meaning that the mapping
-  can only be accessed from within this thread and the thread is bound the
-  CPU while the mapping is active. Even if the thread is preempted (since
-  preemption is never disabled by the function) the CPU can not be
-  unplugged from the system via CPU-hotplug until the mapping is disposed.
+  can only be accessed from within this thread and the thread is bound to the
+  CPU while the mapping is active. Although preemption is never disabled by
+  this function, the CPU can not be unplugged from the system via
+  CPU-hotplug until the mapping is disposed.
 
   It's valid to take pagefaults in a local kmap region, unless the context
   in which the local mapping is acquired does not allow it for other reasons.
 
+  As said, pagefaults and preemption are never disabled. There is no need to
+  disable preemption because, when context switches to a different task, the
+  maps of the outgoing task are saved and those of the incoming one are
+  restored.
+
   kmap_local_page() always returns a valid virtual address and it is assumed
   that kunmap_local() will never fail.
 
_

Patches currently in -mm which might be from fmdefrancesco@xxxxxxxxx are





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