+ mm-add-mm_struct-sequence-number-to-detect-write-locks.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: add mm_struct sequence number to detect write locks
has been added to the -mm mm-unstable branch.  Its filename is
     mm-add-mm_struct-sequence-number-to-detect-write-locks.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-add-mm_struct-sequence-number-to-detect-write-locks.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Suren Baghdasaryan <surenb@google.com>
Subject: mm: add mm_struct sequence number to detect write locks
Date: Sun, 21 Jan 2024 23:13:23 -0800

Provide a way for lockless mm_struct users to detect whether mm might have
been changed since some specific point in time.  The API provided allows
the user to record a counter when it starts using the mm and later use
that counter to check if anyone write-locked mmap_lock since the counter
was recorded.  Recording the counter value should be done while holding
mmap_lock at least for reading to prevent the counter from concurrent
changes.  Every time mmap_lock is write-locked mm_struct updates its
mm_wr_seq counter so that checks against counters recorded before that
would fail, indicating a possibility of mm being modified.

Link: https://lkml.kernel.org/r/20240122071324.2099712-2-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrei Vagin <avagin@google.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Ben Wolsieffer <ben.wolsieffer@hefring.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: T.J. Alumbaugh <talumbau@google.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xingui Yang <yangxingui@huawei.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm_types.h  |    2 ++
 include/linux/mmap_lock.h |   22 ++++++++++++++++++++++
 2 files changed, 24 insertions(+)

--- a/include/linux/mmap_lock.h~mm-add-mm_struct-sequence-number-to-detect-write-locks
+++ a/include/linux/mmap_lock.h
@@ -106,6 +106,8 @@ static inline void mmap_write_lock(struc
 {
 	__mmap_lock_trace_start_locking(mm, true);
 	down_write(&mm->mmap_lock);
+	/* Pairs with ACQUIRE semantics in mmap_write_seq_read */
+	smp_store_release(&mm->mm_wr_seq, mm->mm_wr_seq + 1);
 	__mmap_lock_trace_acquire_returned(mm, true, true);
 }
 
@@ -113,6 +115,8 @@ static inline void mmap_write_lock_neste
 {
 	__mmap_lock_trace_start_locking(mm, true);
 	down_write_nested(&mm->mmap_lock, subclass);
+	/* Pairs with ACQUIRE semantics in mmap_write_seq_read */
+	smp_store_release(&mm->mm_wr_seq, mm->mm_wr_seq + 1);
 	__mmap_lock_trace_acquire_returned(mm, true, true);
 }
 
@@ -122,6 +126,10 @@ static inline int mmap_write_lock_killab
 
 	__mmap_lock_trace_start_locking(mm, true);
 	ret = down_write_killable(&mm->mmap_lock);
+	if (!ret) {
+		/* Pairs with ACQUIRE semantics in mmap_write_seq_read */
+		smp_store_release(&mm->mm_wr_seq, mm->mm_wr_seq + 1);
+	}
 	__mmap_lock_trace_acquire_returned(mm, true, ret == 0);
 	return ret;
 }
@@ -140,6 +148,20 @@ static inline void mmap_write_downgrade(
 	downgrade_write(&mm->mmap_lock);
 }
 
+static inline unsigned long mmap_write_seq_read(struct mm_struct *mm)
+{
+	/* Pairs with RELEASE semantics in mmap_write_lock */
+	return smp_load_acquire(&mm->mm_wr_seq);
+}
+
+static inline void mmap_write_seq_record(struct mm_struct *mm,
+					 unsigned long *mm_wr_seq)
+{
+	mmap_assert_locked(mm);
+	/* Nobody can concurrently modify since we hold the mmap_lock */
+	*mm_wr_seq = mm->mm_wr_seq;
+}
+
 static inline void mmap_read_lock(struct mm_struct *mm)
 {
 	__mmap_lock_trace_start_locking(mm, false);
--- a/include/linux/mm_types.h~mm-add-mm_struct-sequence-number-to-detect-write-locks
+++ a/include/linux/mm_types.h
@@ -845,6 +845,8 @@ struct mm_struct {
 		 */
 		int mm_lock_seq;
 #endif
+		/* Counter incremented each time mm gets write-locked */
+		unsigned long mm_wr_seq;
 
 
 		unsigned long hiwater_rss; /* High-watermark of RSS usage */
_

Patches currently in -mm which might be from surenb@google.com are

mm-make-vm_area_struct-anon_name-field-rcu-safe.patch
mm-add-mm_struct-sequence-number-to-detect-write-locks.patch
mm-maps-read-proc-pid-maps-under-rcu.patch