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@xxxxxxxxxx>
Subject: mm: add mm_struct sequence number to detect write locks
Date: Tue, 23 Jan 2024 15:10:13 -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/20240123231014.3801041-2-surenb@xxxxxxxxxx
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andrei Vagin <avagin@xxxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Ben Wolsieffer <ben.wolsieffer@xxxxxxxxxxx>
Cc: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Dave Chinner <dchinner@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: SeongJae Park <sj@xxxxxxxxxx>
Cc: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Cc: T.J. Alumbaugh <talumbau@xxxxxxxxxx>
Cc: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Xingui Yang <yangxingui@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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
@@ -846,6 +846,8 @@ 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@xxxxxxxxxx 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
