The quilt patch titled
Subject: mm: handle shared faults under the VMA lock
has been removed from the -mm tree. Its filename was
mm-handle-shared-faults-under-the-vma-lock.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Subject: mm: handle shared faults under the VMA lock
Date: Fri, 6 Oct 2023 20:53:15 +0100
There are many implementations of ->fault and some of them depend on
mmap_lock being held. All vm_ops that implement ->map_pages() end up
calling filemap_fault(), which I have audited to be sure it does not rely
on mmap_lock. So (for now) key off ->map_pages existing as a flag to
indicate that it's safe to call ->fault while only holding the vma lock.
Link: https://lkml.kernel.org/r/20231006195318.4087158-4-willy@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)
--- a/mm/memory.c~mm-handle-shared-faults-under-the-vma-lock
+++ a/mm/memory.c
@@ -3042,6 +3042,21 @@ static inline void wp_page_reuse(struct
count_vm_event(PGREUSE);
}
+/*
+ * We could add a bitflag somewhere, but for now, we know that all
+ * vm_ops that have a ->map_pages have been audited and don't need
+ * the mmap_lock to be held.
+ */
+static inline vm_fault_t vmf_can_call_fault(const struct vm_fault *vmf)
+{
+ struct vm_area_struct *vma = vmf->vma;
+
+ if (vma->vm_ops->map_pages || !(vmf->flags & FAULT_FLAG_VMA_LOCK))
+ return 0;
+ vma_end_read(vma);
+ return VM_FAULT_RETRY;
+}
+
static vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
@@ -4669,10 +4684,9 @@ static vm_fault_t do_shared_fault(struct
vm_fault_t ret, tmp;
struct folio *folio;
- if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
- vma_end_read(vma);
- return VM_FAULT_RETRY;
- }
+ ret = vmf_can_call_fault(vmf);
+ if (ret)
+ return ret;
ret = __do_fault(vmf);
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are
buffer-make-folio_create_empty_buffers-return-a-buffer_head.patch
mpage-convert-map_buffer_to_folio-to-folio_create_empty_buffers.patch
ext4-convert-to-folio_create_empty_buffers.patch
buffer-add-get_nth_bh.patch
gfs2-convert-inode-unstuffing-to-use-a-folio.patch
gfs2-convert-gfs2_getbuf-to-folios.patch
gfs2-convert-gfs2_getjdatabuf-to-use-a-folio.patch
gfs2-convert-gfs2_write_buf_to_page-to-use-a-folio.patch
nilfs2-convert-nilfs_mdt_freeze_buffer-to-use-a-folio.patch
nilfs2-convert-nilfs_grab_buffer-to-use-a-folio.patch
nilfs2-convert-nilfs_copy_page-to-nilfs_copy_folio.patch
nilfs2-convert-nilfs_mdt_forget_block-to-use-a-folio.patch
nilfs2-convert-nilfs_mdt_get_frozen_buffer-to-use-a-folio.patch
nilfs2-remove-nilfs_page_get_nth_block.patch
nilfs2-convert-nilfs_lookup_dirty_data_buffers-to-use-folio_create_empty_buffers.patch
ntfs-convert-ntfs_read_block-to-use-a-folio.patch
ntfs-convert-ntfs_writepage-to-use-a-folio.patch
ntfs-convert-ntfs_prepare_pages_for_non_resident_write-to-folios.patch
ntfs3-convert-ntfs_zero_range-to-use-a-folio.patch
ocfs2-convert-ocfs2_map_page_blocks-to-use-a-folio.patch
reiserfs-convert-writepage-to-use-a-folio.patch
ufs-add-ufs_get_locked_folio-and-ufs_put_locked_folio.patch
ufs-use-ufs_get_locked_folio-in-ufs_alloc_lastblock.patch
ufs-convert-ufs_change_blocknr-to-use-folios.patch
ufs-remove-ufs_get_locked_page.patch
buffer-remove-folio_create_empty_buffers.patch
