[to-be-updated] mm-vma-fix-mmap_prepare-file-handling-remove-file_doesnt_need_get.patch removed from -mm tree

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

The quilt patch titled
     Subject: mm/vma: fix mmap_prepare file handling, remove file_doesnt_need_get
has been removed from the -mm tree.  Its filename was
     mm-vma-fix-mmap_prepare-file-handling-remove-file_doesnt_need_get.patch

This patch was dropped because an updated version will be issued

------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Subject: mm/vma: fix mmap_prepare file handling, remove file_doesnt_need_get
Date: Sat, 03 Oct 2026 17:32:32 +0100

The map->file_doesnt_need_get flag is confusing and the existing
implementation has holes.

Drivers are permitted to change the owning file of a mapping. If they do
so, they are required to take a reference on that file.

The mmap() operation which ultimately invokes __mmap_region() is guaranteed
to drop the refcount for the original file the mapping was made under, but
this is not true for the replaced file.

This has been addressed so far by tracking map->file_doesnt_need_get, which
is rather poorly named and unfortunately fails to correctly track whether
or not an additional put were needed in a number of cases.

Make life easier by removing this flag, and instead drop the reference for
both mmap_prepare and the deprecated mmap callback in a new function
map_put_vm_file().

Track whether this needs to be done by aligning mmap_state with
vm_area_desc and store the original file in the map->file field, keeping
the updated file in map->vm_file.

In order to have the same behaviour for both types of hooks, only drop the
reference __mmap_new_file_vma() itself took in its error path, deferring
the replaced file's reference to map_put_vm_file().

To make this work correctly, map->vm_file has to be updated before any
error handling, so update __mmap_new_file_vma() and call_mmap_prepare() to
set this field first.

Also when mmap_prepare() changes the file and is then merged, the reference
count also must be decremented, so update the logic to call
map_put_vm_file() in this case too.

Also update __compat_vma_mmap() to manually perform this step for stacked
file systems using the compatibility layer, and update
compat_set_vma_from_desc() to replace vma_set_file() with a correct
refcount/file update.

No in-tree driver is impacted by the incorrect implementation of this
currently (no driver that does this is mergeable for one), so this does not
need to be a fix.

Link: https://lore.kernel.org/20261003-b4-mmap-prepare-vma-flag-sanify-v4-1-a1f052500fd7@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: David Hildenbrand <david@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Doug Gilbert <dgilbert@interlog.com>
Cc: James Bottomley <james.bottomley@hansenpartnership.com>
Cc: Martin K. Petersen <mkp@kernel.org>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Helge Deller <deller@gmx.de>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Anup Patel <anup@brainfault.org>
Cc: Paul Walmsley <pjw@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Youngjun Park <youngjun.park@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Xu Xin <xu.xin@linux.dev>
---

 mm/internal.h |    1 
 mm/util.c     |    5 ++
 mm/vma.c      |   81 +++++++++++++++++++++++++++++-------------------
 mm/vma.h      |    6 ++-
 4 files changed, 58 insertions(+), 35 deletions(-)

--- a/mm/internal.h~mm-vma-fix-mmap_prepare-file-handling-remove-file_doesnt_need_get
+++ a/mm/internal.h
@@ -7,6 +7,7 @@
 #ifndef __MM_INTERNAL_H
 #define __MM_INTERNAL_H
 
+#include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/khugepaged.h>
 #include <linux/mm.h>
--- a/mm/util.c~mm-vma-fix-mmap_prepare-file-handling-remove-file_doesnt_need_get
+++ a/mm/util.c
@@ -1228,8 +1228,11 @@ int __compat_vma_mmap(struct vm_area_des
 
 	/* Perform any preparatory tasks for mmap action. */
 	err = mmap_action_prepare(desc);
-	if (err)
+	if (err) {
+		if (desc->vm_file != vma->vm_file)
+			fput(desc->vm_file);
 		return err;
+	}
 	/* Update the VMA from the descriptor. */
 	compat_set_vma_from_desc(vma, desc);
 	/* Complete any specified mmap actions. */
--- a/mm/vma.c~mm-vma-fix-mmap_prepare-file-handling-remove-file_doesnt_need_get
+++ a/mm/vma.c
@@ -24,7 +24,8 @@ struct mmap_state {
 		vm_flags_t vm_flags;
 		vma_flags_t vma_flags;
 	};
-	struct file *file;
+	struct file *file;	/* mmap()-specified file. */
+	struct file *vm_file;	/* May be updated by mmap_prepare. */
 	pgprot_t page_prot;
 
 	/* User-defined fields, perhaps updated by .mmap_prepare(). */
@@ -43,8 +44,6 @@ struct mmap_state {
 
 	/* Determine if we can check KSM flags early in mmap() logic. */
 	bool check_ksm_early :1;
-	/* If .mmap_prepare changed the file, we don't need to pin. */
-	bool file_doesnt_need_get :1;
 };
 
 #define MMAP_STATE(name, mm_, vmi_, addr_, len_, pgoff_, anon_pgoff_, vma_flags_, file_) \
@@ -58,6 +57,7 @@ struct mmap_state {
 		.pglen = PHYS_PFN(len_),				\
 		.vma_flags = vma_flags_,				\
 		.file = file_,						\
+		.vm_file = file_,					\
 		.page_prot = vma_flags_to_page_prot(vma_flags_),	\
 	}
 
@@ -70,7 +70,7 @@ struct mmap_state {
 		.vma_flags = (map_)->vma_flags,				\
 		.pgoff = (map_)->pgoff,					\
 		.anon_pgoff = (map_)->anon_pgoff,			\
-		.file = (map_)->file,					\
+		.file = (map_)->vm_file,				\
 		.prev = (map_)->prev,					\
 		.middle = vma_,						\
 		.next = (vma_) ? NULL : (map_)->next,			\
@@ -2462,7 +2462,7 @@ void mm_drop_all_locks(struct mm_struct
  */
 static bool accountable_mapping(struct mmap_state *map)
 {
-	const struct file *file = map->file;
+	const struct file *file = map->vm_file;
 
 	/*
 	 * hugetlb has its own accounting separate from the core VM
@@ -2511,7 +2511,7 @@ static void vms_abort_munmap_vmas(struct
 
 static void update_ksm_flags(struct mmap_state *map)
 {
-	map->vma_flags = ksm_vma_flags(map->mm, map->file, map->vma_flags);
+	map->vma_flags = ksm_vma_flags(map->mm, map->vm_file, map->vma_flags);
 }
 
 static void set_desc_from_map(struct vm_area_desc *desc,
@@ -2521,7 +2521,7 @@ static void set_desc_from_map(struct vm_
 	desc->end = map->end;
 
 	desc->pgoff = map->pgoff;
-	desc->vm_file = map->file;
+	desc->vm_file = map->vm_file;
 	desc->vma_flags = map->vma_flags;
 	desc->page_prot = map->page_prot;
 }
@@ -2601,6 +2601,10 @@ static int __mmap_setup(struct mmap_stat
 	return 0;
 }
 
+static bool map_same_file(struct mmap_state *map)
+{
+	return map->vm_file == map->file;
+}
 
 static int __mmap_new_file_vma(struct mmap_state *map,
 			       struct vm_area_struct *vma)
@@ -2608,20 +2612,23 @@ static int __mmap_new_file_vma(struct mm
 	struct vma_iterator *vmi = map->vmi;
 	int error;
 
-	vma->vm_file = map->file;
-	if (!map->file_doesnt_need_get)
-		get_file(map->file);
+	vma->vm_file = map->vm_file;
+	if (map_same_file(map))
+		get_file(map->vm_file);
 
-	if (!map->file->f_op->mmap)
+	if (!map->vm_file->f_op->mmap)
 		return 0;
 
 	error = mmap_file(vma->vm_file, vma);
+	map->vm_file = vma->vm_file;
+
 	if (error) {
 		UNMAP_STATE(unmap, vmi, vma, vma->vm_start, vma->vm_end,
 			    map->prev, map->next);
-		fput(vma->vm_file);
-		vma->vm_file = NULL;
+		if (map_same_file(map))
+			fput(map->vm_file);
 
+		vma->vm_file = NULL;
 		vma_iter_set(vmi, vma->vm_end);
 		/* Undo any partial mapping done by a device driver. */
 		unmap_region(&unmap);
@@ -2638,7 +2645,6 @@ static int __mmap_new_file_vma(struct mm
 			!vma_flags_test(&map->vma_flags, VMA_MAYWRITE_BIT) &&
 			vma_test(vma, VMA_MAYWRITE_BIT));
 
-	map->file = vma->vm_file;
 	map->vma_flags = vma->flags;
 
 	return 0;
@@ -2646,7 +2652,7 @@ static int __mmap_new_file_vma(struct mm
 
 static void map_set_anon(struct mmap_state *map)
 {
-	map->file = NULL;
+	map->vm_file = NULL;
 	map->vm_ops = NULL;
 	map->pgoff = map->addr >> PAGE_SHIFT;
 }
@@ -2658,7 +2664,7 @@ static bool map_is_private(const struct
 
 static bool map_is_anon(const struct mmap_state *map)
 {
-	return map_is_private(map) && !map->file;
+	return map_is_private(map) && !map->vm_file;
 }
 
 /*
@@ -2703,7 +2709,7 @@ static int __mmap_new_vma(struct mmap_st
 	}
 
 	/* Invoke callbacks. */
-	if (map->file)
+	if (map->vm_file)
 		error = __mmap_new_file_vma(map, vma);
 	else if (!is_anon)
 		error = shmem_zero_setup(vma);
@@ -2812,10 +2818,14 @@ static int call_mmap_prepare(struct mmap
 	int err;
 
 	/* Invoke the hook. */
-	err = vfs_mmap_prepare(map->file, desc);
+	err = vfs_mmap_prepare(map->vm_file, desc);
 	if (err)
 		return err;
 
+	/* Update first so file refcount tracked correctly. */
+	if (desc->vm_file != map->vm_file)
+		map->vm_file = desc->vm_file;
+
 	/* It's invalid for mmap_prepare hooks to clear vm_ops. */
 	if (!desc->vm_ops)
 		return -EINVAL;
@@ -2826,10 +2836,6 @@ static int call_mmap_prepare(struct mmap
 
 	/* Update fields permitted to be changed. */
 	map->pgoff = desc->pgoff;
-	if (desc->vm_file != map->file) {
-		map->file_doesnt_need_get = true;
-		map->file = desc->vm_file;
-	}
 	map->vma_flags = desc->vma_flags;
 	map->page_prot = desc->page_prot;
 	/* User-defined fields. */
@@ -2841,7 +2847,7 @@ static int call_mmap_prepare(struct mmap
 	 * anonymous mappings. Rather than allowing these mappings to be odd
 	 * outliers, simply make them truly anonymous.
 	 */
-	if (map_is_private(map) && file_is_dev_zero(map->file))
+	if (map_is_private(map) && file_is_dev_zero(map->vm_file))
 		map_set_anon(map);
 
 	return 0;
@@ -2860,7 +2866,7 @@ static void set_vma_user_defined_fields(
  */
 static bool can_set_ksm_flags_early(struct mmap_state *map)
 {
-	struct file *file = map->file;
+	struct file *file = map->vm_file;
 
 	/* Anonymous mappings have no driver which can change them. */
 	if (!file)
@@ -2883,6 +2889,20 @@ static bool can_set_ksm_flags_early(stru
 	return false;
 }
 
+static void map_put_vm_file(struct mmap_state *map)
+{
+	/*
+	 * An error occurred or the VMA was merged.
+	 *
+	 * If the file was changed by the driver (which is required to increment
+	 * the replacement file's reference count), drop its reference count.
+	 *
+	 * On error, the caller always drops the original file regardless.
+	 */
+	if (map->vm_file && !map_same_file(map))
+		fput(map->vm_file);
+}
+
 static unsigned long __mmap_region(struct file *file, unsigned long addr,
 		unsigned long len, vma_flags_t vma_flags,
 		unsigned long pgoff, struct list_head *uf)
@@ -2937,7 +2957,10 @@ static unsigned long __mmap_region(struc
 
 	__mmap_complete(&map, vma);
 
-	if (have_mmap_prepare && allocated_new) {
+	if (!allocated_new) {
+		/* Merged, so need to drop refcount. */
+		map_put_vm_file(&map);
+	} else if (have_mmap_prepare) {
 		error = mmap_action_complete(vma, &desc.action,
 					     /*is_compat=*/false);
 		if (error)
@@ -2951,13 +2974,7 @@ unacct_error:
 	if (map.charged)
 		vm_unacct_memory(map.charged);
 abort_munmap:
-	/*
-	 * This indicates that .mmap_prepare has set a new file, differing from
-	 * desc->vm_file. But since we're aborting the operation, only the
-	 * original file will be cleaned up. Ensure we clean up both.
-	 */
-	if (map.file_doesnt_need_get)
-		fput(map.file);
+	map_put_vm_file(&map);
 	vms_abort_munmap_vmas(&map.vms, &map.mas_detach);
 	return error;
 }
--- a/mm/vma.h~mm-vma-fix-mmap_prepare-file-handling-remove-file_doesnt_need_get
+++ a/mm/vma.h
@@ -394,8 +394,10 @@ static inline void compat_set_vma_from_d
 
 	/* Mutable fields. Populated with initial state. */
 	vma_set_pgoff(vma, desc->pgoff);
-	if (desc->vm_file != vma->vm_file)
-		vma_set_file(vma, desc->vm_file);
+	if (desc->vm_file != vma->vm_file) {
+		fput(vma->vm_file);
+		vma->vm_file = desc->vm_file;
+	}
 	vma->flags = desc->vma_flags;
 	vma->vm_page_prot = desc->page_prot;
 
_

Patches currently in -mm which might be from ljs@kernel.org are

mm-vma-introduce-and-use-vma_can_merge.patch
mm-consistently-validate-vma-state-after-mmap-hooks.patch
mm-vma-ensure-mmap_prepare-doesnt-set-actions-on-a-mergeable-vma.patch
mm-make-map_kernel_pages_-internal-and-unexported.patch
mm-vma-tidy-up-map-kernel-pages-enum-values.patch
mm-add-mmap-action-for-discontiguous-kernel-page-mapping.patch
docs-filesystems-update-mmap_prepare-docs-for-discontig-kernel-pgs.patch
drivers-usb-mon-update-to-use-mmap_prepare-map-kernel-pages.patch
infiniband-update-hfi1-to-use-remap_vmalloc_range.patch
selinux-reject-writable-opens-of-policy-file-drop-mmap-shared-write-check.patch
alsa-pcm-use-vm_insert_page-to-map-pcm-status-page.patch
bpf-arena-mark-arena_map_mmap-mappings-vm_mixedmap.patch
mm-vma-add-vma_is_mm_managed-predicates.patch
mm-vma-only-allow-mmap-to-clear-vma_maywrite_bit-if-not-mm-managed.patch
mm-vma-add-and-use-vma__is_fixed_mapping.patch
scsi-sg-convert-mmap-hook-to-mmap_prepare-and-rework.patch
fbdev-defio-assert-fbinfo_virtfb-drop-vm_io-add-vm_mixedmap.patch
hsi-cmt_speech-convert-mmap-hook-to-mmap_prepare-refactor.patch
mm-gup-error-out-early-on-vma_mayread_bit-vmas.patch
uprobes-remove-vm_io-set-vm_mixedmap-for-mapped-kernel-pages.patch
mm-mlock-clear-vma_locked_mask-over-mmap-callback.patch
mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify.patch
mm-vma-enforce-that-mm-managed-mappings-may-not-set-vma_io_bit.patch
mm-remove-vma_io_bit-check-in-vma_is_mm_managed.patch
mm-remove-hugetlb_inlineh.patch
mm-rename-is_vm_hugetlb_page-to-vma_is_hugetlb.patch
mm-drop-some-redundant-checks-around-hugetlb-vmas.patch
mm-madvise-update-is_valid_guard_vma-to-use-vma_can_merge.patch
mm-vma-introduce-vma_is_mm_backed.patch
mm-uffd-use-predicates-for-userfaultfd-checks.patch
mm-madvise-use-predicates-for-madvise-madv_dofork.patch
mm-eliminate-vma_special_flags-usage-when-hugetlb-explicitly-tested.patch
mm-eliminate-vma_special_flags-check-in-lru_gen_look_around.patch
mm-avoid-use-of-vma_special_flags-in-migrate_vma_setup.patch
mm-eliminate-vm_special-vma_special_flags.patch
fuse-dax-do-not-set-vm_mixedmap.patch
mm-huge_memory-remove-vma_is_special_huge.patch
mm-vma-const-ify-vma_assert_stabilised-and-associated-functions.patch
mm-implement-and-use-vma_has_anon_rmap-silence-kcsan.patch
mm-update-comments-to-refer-to-anon-rmap-rather-than-anon_vma.patch
mm-vma-dont-remove-vma-from-rmap-if-pgoff-unchanged.patch