+ mm-assert-the-mmap_lock-is-held-in-__anon_vma_prepare.patch added to mm-unstable branch

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

The patch titled
     Subject: mm: assert the mmap_lock is held in __anon_vma_prepare()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-assert-the-mmap_lock-is-held-in-__anon_vma_prepare.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-assert-the-mmap_lock-is-held-in-__anon_vma_prepare.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: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: mm: assert the mmap_lock is held in __anon_vma_prepare()
Date: Fri, 26 Apr 2024 15:45:00 +0100

Patch series "Improve anon_vma scalability for anon VMAs".

We have a 3x throughput improvement reported by Intel's kernel test robot:
https://lore.kernel.org/all/202404261055.c5e24608-oliver.sang@intel.com/

This is from delaying taking the mmap_lock for page faults until we
actually need the mmap_lock in order to assign an anon_vma to the vma.  It
cleans up the page fault path a little by making the anon fault handler
more similar to the file fault handler.


This patch (of 4):

Convert the comment into an assertion.

Link: https://lkml.kernel.org/r/20240426144506.1290619-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20240426144506.1290619-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/rmap.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/mm/rmap.c~mm-assert-the-mmap_lock-is-held-in-__anon_vma_prepare
+++ a/mm/rmap.c
@@ -182,8 +182,6 @@ static void anon_vma_chain_link(struct v
  * for the new allocation. At the same time, we do not want
  * to do any locking for the common case of already having
  * an anon_vma.
- *
- * This must be called with the mmap_lock held for reading.
  */
 int __anon_vma_prepare(struct vm_area_struct *vma)
 {
@@ -191,6 +189,7 @@ int __anon_vma_prepare(struct vm_area_st
 	struct anon_vma *anon_vma, *allocated;
 	struct anon_vma_chain *avc;
 
+	mmap_assert_locked(mm);
 	might_sleep();
 
 	avc = anon_vma_chain_alloc(GFP_KERNEL);
_

Patches currently in -mm which might be from willy@infradead.org are

doc-improve-the-description-of-__folio_mark_dirty.patch
buffer-add-kernel-doc-for-block_dirty_folio.patch
buffer-add-kernel-doc-for-try_to_free_buffers.patch
buffer-fix-__bread-and-__bread_gfp-kernel-doc.patch
buffer-add-kernel-doc-for-brelse-and-__brelse.patch
buffer-add-kernel-doc-for-bforget-and-__bforget.patch
buffer-improve-bdev_getblk-documentation.patch
doc-split-bufferrst-out-of-api-summaryrst.patch
doc-split-bufferrst-out-of-api-summaryrst-fix.patch
mm-memory-failure-remove-fsdax_pgoff-argument-from-__add_to_kill.patch
mm-memory-failure-pass-addr-to-__add_to_kill.patch
mm-return-the-address-from-page_mapped_in_vma.patch
mm-make-page_mapped_in_vma-conditional-on-config_memory_failure.patch
mm-memory-failure-convert-shake_page-to-shake_folio.patch
mm-convert-hugetlb_page_mapping_lock_write-to-folio.patch
mm-memory-failure-convert-memory_failure-to-use-a-folio.patch
mm-memory-failure-convert-hwpoison_user_mappings-to-take-a-folio.patch
mm-memory-failure-add-some-folio-conversions-to-unpoison_memory.patch
mm-memory-failure-use-folio-functions-throughout-collect_procs.patch
mm-memory-failure-pass-the-folio-to-collect_procs_ksm.patch
fscrypt-convert-bh_get_inode_and_lblk_num-to-use-a-folio.patch
f2fs-convert-f2fs_clear_page_cache_dirty_tag-to-use-a-folio.patch
memory-failure-remove-calls-to-page_mapping.patch
migrate-expand-the-use-of-folio-in-__migrate_device_pages.patch
userfault-expand-folio-use-in-mfill_atomic_install_pte.patch
mm-remove-page_mapping.patch
mm-remove-page_cache_alloc.patch
mm-remove-put_devmap_managed_page.patch
mm-convert-put_devmap_managed_page_refs-to-put_devmap_managed_folio_refs.patch
mm-remove-page_ref_sub_return.patch
gup-use-folios-for-gup_devmap.patch
mm-add-kernel-doc-for-folio_mark_accessed.patch
mm-remove-pagereferenced.patch
mm-simplify-thp_vma_allowable_order.patch
mm-assert-the-mmap_lock-is-held-in-__anon_vma_prepare.patch
mm-delay-the-check-for-a-null-anon_vma.patch
mm-fix-some-minor-per-vma-lock-issues-in-userfaultfd.patch
mm-optimise-vmf_anon_prepare-for-vmas-without-an-anon_vma.patch