From 1b32952b0dc5103765d88bf4761ec65dddc6a879 Mon Sep 17 00:00:00 2001
From: Michel Lespinasse <walken@google.com>
Date: Mon, 8 Jun 2020 21:33:14 -0700
Subject: mmap locking API: initial implementation as rwsem wrappers
Git-commit: 9740ca4e95b43b91a4a848694a20d01ba6818f7b
Patch-mainline: v5.8-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322

This patch series adds a new mmap locking API replacing the existing
mmap_sem lock and unlocks.  Initially the API is just implemente in terms
of inlined rwsem calls, so it doesn't provide any new functionality.

There are two justifications for the new API:

- At first, it provides an easy hooking point to instrument mmap_sem
  locking latencies independently of any other rwsems.

- In the future, it may be a starting point for replacing the rwsem
  implementation with a different one, such as range locks.  This is
  something that is being explored, even though there is no wide concensus
  about this possible direction yet.  (see
  https://patchwork.kernel.org/cover/11401483/)

This patch (of 12):

This change wraps the existing mmap_sem related rwsem calls into a new
mmap locking API.  There are two justifications for the new API:

- At first, it provides an easy hooking point to instrument mmap_sem
  locking latencies independently of any other rwsems.

- In the future, it may be a starting point for replacing the rwsem
  implementation with a different one, such as range locks.

Signed-off-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Liam Howlett <Liam.Howlett@oracle.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ying Han <yinghan@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Michel Lespinasse <walken@google.com>
Link: http://lkml.kernel.org/r/20200520052908.204642-1-walken@google.com
Link: http://lkml.kernel.org/r/20200520052908.204642-2-walken@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 include/linux/mm.h        |  1 +
 include/linux/mmap_lock.h | 54 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)
 create mode 100644 include/linux/mmap_lock.h

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f3fe7371855c..584591dc246e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -15,6 +15,7 @@
 #include <linux/atomic.h>
 #include <linux/debug_locks.h>
 #include <linux/mm_types.h>
+#include <linux/mmap_lock.h>
 #include <linux/range.h>
 #include <linux/pfn.h>
 #include <linux/percpu-refcount.h>
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
new file mode 100644
index 000000000000..97ac53b66052
--- /dev/null
+++ b/include/linux/mmap_lock.h
@@ -0,0 +1,54 @@
+#ifndef _LINUX_MMAP_LOCK_H
+#define _LINUX_MMAP_LOCK_H
+
+static inline void mmap_init_lock(struct mm_struct *mm)
+{
+	init_rwsem(&mm->mmap_sem);
+}
+
+static inline void mmap_write_lock(struct mm_struct *mm)
+{
+	down_write(&mm->mmap_sem);
+}
+
+static inline int mmap_write_lock_killable(struct mm_struct *mm)
+{
+	return down_write_killable(&mm->mmap_sem);
+}
+
+static inline bool mmap_write_trylock(struct mm_struct *mm)
+{
+	return down_write_trylock(&mm->mmap_sem) != 0;
+}
+
+static inline void mmap_write_unlock(struct mm_struct *mm)
+{
+	up_write(&mm->mmap_sem);
+}
+
+static inline void mmap_write_downgrade(struct mm_struct *mm)
+{
+	downgrade_write(&mm->mmap_sem);
+}
+
+static inline void mmap_read_lock(struct mm_struct *mm)
+{
+	down_read(&mm->mmap_sem);
+}
+
+static inline int mmap_read_lock_killable(struct mm_struct *mm)
+{
+	return down_read_killable(&mm->mmap_sem);
+}
+
+static inline bool mmap_read_trylock(struct mm_struct *mm)
+{
+	return down_read_trylock(&mm->mmap_sem) != 0;
+}
+
+static inline void mmap_read_unlock(struct mm_struct *mm)
+{
+	up_read(&mm->mmap_sem);
+}
+
+#endif /* _LINUX_MMAP_LOCK_H */
-- 
2.28.0