On Thu, Nov 21, 2024 at 4:40 AM Peter Zijlstra [off-list ref] wrote:

On Sun, Oct 27, 2024 at 06:08:15PM -0700, Andrii Nakryiko wrote:

quoted

+/*
+ * Drop all currently-held per-VMA locks.
+ * This is called from the mmap_lock implementation directly before releasing
+ * a write-locked mmap_lock (or downgrading it to read-locked).
+ * This should normally NOT be called manually from other places.
+ * If you want to call this manually anyway, keep in mind that this will release
+ * *all* VMA write locks, including ones from further up the stack.
+ */
+static inline void vma_end_write_all(struct mm_struct *mm)
+{
+     mmap_assert_write_locked(mm);
+     /*
+      * Nobody can concurrently modify mm->mm_lock_seq due to exclusive
+      * mmap_lock being held.
+      */

You can write:

        ASSERT_EXCLUSIVE_WRITER(mm->mm_lock_seq);

instead of that comment. Then KCSAN will validate the claim.

Thanks for the tip! This one looks not critical but I see there are
more important comments in "mm: Introduce
mmap_lock_speculation_{begin|end}". I'll send a new version shortly.

quoted

+     mm_lock_seqcount_end(mm);
+}