linux-kernel - [PATCH v4 5/5] docs/mm: document latest changes to vm

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Message-ID: <20241120000826.335387-6-surenb@google.com>
Date: Tue, 19 Nov 2024 16:08:26 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: akpm@...ux-foundation.org
Cc: willy@...radead.org, liam.howlett@...cle.com, lorenzo.stoakes@...cle.com, 
	mhocko@...e.com, vbabka@...e.cz, hannes@...xchg.org, mjguzik@...il.com, 
	oliver.sang@...el.com, mgorman@...hsingularity.net, david@...hat.com, 
	peterx@...hat.com, oleg@...hat.com, dave@...olabs.net, paulmck@...nel.org, 
	brauner@...nel.org, dhowells@...hat.com, hdanton@...a.com, hughd@...gle.com, 
	minchan@...gle.com, jannh@...gle.com, shakeel.butt@...ux.dev, 
	souravpanda@...gle.com, pasha.tatashin@...een.com, corbet@....net, 
	linux-doc@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	kernel-team@...roid.com, surenb@...gle.com
Subject: [PATCH v4 5/5] docs/mm: document latest changes to vm_lock

Change the documentation to reflect that vm_lock is integrated into vma.
Document newly introduced vma_start_read_locked{_nested} functions.

Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 Documentation/mm/process_addrs.rst | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/Documentation/mm/process_addrs.rst b/Documentation/mm/process_addrs.rst
index 1bf7ad010fc0..a18450b6496d 100644
--- a/Documentation/mm/process_addrs.rst
+++ b/Documentation/mm/process_addrs.rst
@@ -686,7 +686,11 @@ calls :c:func:`!rcu_read_lock` to ensure that the VMA is looked up in an RCU
 critical section, then attempts to VMA lock it via :c:func:`!vma_start_read`,
 before releasing the RCU lock via :c:func:`!rcu_read_unlock`.
 
-VMA read locks hold the read lock on the :c:member:`!vma->vm_lock` semaphore for
+In cases when the user already holds mmap read lock, :c:func:`!vma_start_read_locked`
+and :c:func:`!vma_start_read_locked_nested` can be used. These functions always
+succeed in acquiring VMA read lock.
+
+VMA read locks hold the read lock on the :c:member:`!vma.vm_lock` semaphore for
 their duration and the caller of :c:func:`!lock_vma_under_rcu` must release it
 via :c:func:`!vma_end_read`.
 
@@ -750,7 +754,7 @@ keep VMAs locked across entirely separate write operations. It also maintains
 correct lock ordering.
 
 Each time a VMA read lock is acquired, we acquire a read lock on the
-:c:member:`!vma->vm_lock` read/write semaphore and hold it, while checking that
+:c:member:`!vma.vm_lock` read/write semaphore and hold it, while checking that
 the sequence count of the VMA does not match that of the mm.
 
 If it does, the read lock fails. If it does not, we hold the lock, excluding
@@ -760,7 +764,7 @@ Importantly, maple tree operations performed in :c:func:`!lock_vma_under_rcu`
 are also RCU safe, so the whole read lock operation is guaranteed to function
 correctly.
 
-On the write side, we acquire a write lock on the :c:member:`!vma->vm_lock`
+On the write side, we acquire a write lock on the :c:member:`!vma.vm_lock`
 read/write semaphore, before setting the VMA's sequence number under this lock,
 also simultaneously holding the mmap write lock.
 
-- 
2.47.0.338.g60cca15819-goog