Introduce a new mempool_alloc_preallocated API that asks the mempool to
only use the elements preallocated during the mempool's creation when
allocating and to not attempt allocating new ones from the underlying
allocator.

This API is required to test the KASAN poisoning/unpoisoning functionality
in KASAN tests, but it might be also useful on its own.

Link: https://lkml.kernel.org/r/a14d809dbdfd04cc33bcacc632fee2abd6b83c00.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>

Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Update the mempool code to use the new mempool KASAN hooks.

Rely on the return value of kasan_mempool_poison_object and
kasan_mempool_poison_pages to prevent double-free and invalid-free bugs.

Link: https://lkml.kernel.org/r/d36fc4a6865bdbd297cadb46b67641d436849f4c.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

With the changes in the following patch, KASAN starts saving its metadata
within freed mempool elements.

Thus, skip slub_debug poisoning and checking of mempool elements when
KASAN is enabled.  Corruptions of freed mempool elements will be detected
by KASAN anyway.

Link: https://lkml.kernel.org/r/98a4b1617e8ceeb266ef9a46f5e8c7f67a563ad2.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>

Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Update kasan_mempool_unpoison_object to properly poison the redzone and
save alloc strack traces for kmalloc and slab pools.

As a part of this change, split out and use a unpoison_slab_object helper
function from __kasan_slab_alloc.

[nathan@kernel.org: mark unpoison_slab_object() as static]
  Link: https://lkml.kernel.org/r/20231221180042.104694-1-andrey.konovalov@linux.dev
Link: https://lkml.kernel.org/r/05ad235da8347cfe14d496d01b2aaf074b4f607c.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Split out a poison_kmalloc_large_redzone helper from __kasan_kmalloc_large
and use it in the caller's code.

This is a preparatory change for the following patches in this series.

Link: https://lkml.kernel.org/r/93317097b668519d76097fb065201b2027436e22.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Introduce a new poison_kmalloc_redzone helper function that poisons the
redzone for kmalloc object.

Drop the confusingly named ____kasan_kmalloc function and instead use
poison_kmalloc_redzone along with the other required parts of
____kasan_kmalloc in the callers' code.

This is a preparatory change for the following patches in this series.

Link: https://lkml.kernel.org/r/5881232ad357ec0d59a5b1aefd9e0673a386399a.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Make kasan_mempool_poison_object save free stack traces for slab and
kmalloc mempools when the object is freed into the mempool.

Also simplify and rename ____kasan_slab_free to poison_slab_object and do
a few other reability changes.

Link: https://lkml.kernel.org/r/413a7c7c3344fb56809853339ffaabc9e4905e94.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Reorganize the code and reword the comment in
__kasan_mempool_poison_object to improve the code readability.

Link: https://lkml.kernel.org/r/4f6fc8840512286c1a96e16e86901082c671677d.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Introduce and document a new kasan_mempool_unpoison_pages hook to be used
by the mempool code instead of kasan_unpoison_pages.

This hook is not functionally different from kasan_unpoison_pages, but
using it improves the mempool code readability.

Link: https://lkml.kernel.org/r/239bd9af6176f2cc59f5c25893eb36143184daff.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Introduce and document a kasan_mempool_poison_pages hook to be used by the
mempool code instead of kasan_poison_pages.

Compated to kasan_poison_pages, the new hook:

1. For the tag-based modes, skips checking and poisoning allocations that
   were not tagged due to sampling.

2. Checks for double-free and invalid-free bugs.

In the future, kasan_poison_pages can also be updated to handle #2, but
this is out-of-scope of this series.

Link: https://lkml.kernel.org/r/88dc7340cce28249abf789f6e0c792c317df9ba5.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Introduce and document a kasan_mempool_unpoison_object hook.

This hook serves as a replacement for the generic kasan_unpoison_range
that the mempool code relies on right now.  mempool will be updated to use
the new hook in one of the following patches.

For now, define the new hook to be identical to kasan_unpoison_range.  One
of the following patches will update it to add stack trace collection.

Link: https://lkml.kernel.org/r/dae25f0e18ed8fd50efe509c5b71a0592de5c18d.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Add a return value for kasan_mempool_poison_object that lets the caller
know whether the allocation is affected by a double-free or an
invalid-free bug.  The caller can use this return value to stop operating
on the object.

Also introduce a check_page_allocation helper function to improve the code
readability.

Link: https://lkml.kernel.org/r/618af65273875fb9f56954285443279b15f1fcd9.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Add documentation comment for kasan_mempool_poison_object.

Link: https://lkml.kernel.org/r/af33ba8cabfa1ad731fe23a3f874bfc8d3b7fed4.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Move kasan_mempool_poison_object after all slab-related KASAN hooks.

This is a preparatory change for the following patches in this series.

No functional changes.

Link: https://lkml.kernel.org/r/23ea215409f43c13cdf9ecc454501a264c107d67.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Patch series "kasan: save mempool stack traces".

This series updates KASAN to save alloc and free stack traces for
secondary-level allocators that cache and reuse allocations internally
instead of giving them back to the underlying allocator (e.g.  mempool).

As a part of this change, introduce and document a set of KASAN hooks:

bool kasan_mempool_poison_pages(struct page *page, unsigned int order);
void kasan_mempool_unpoison_pages(struct page *page, unsigned int order);
bool kasan_mempool_poison_object(void *ptr);
void kasan_mempool_unpoison_object(void *ptr, size_t size);

and use them in the mempool code.

Besides mempool, skbuff and io_uring also cache allocations and already
use KASAN hooks to poison those.  Their code is updated to use the new
mempool hooks.

The new hooks save alloc and free stack traces (for normal kmalloc and
slab objects; stack traces for large kmalloc objects and page_alloc are
not supported by KASAN yet), improve the readability of the users' code,
and also allow the users to prevent double-free and invalid-free bugs; see
the patches for the details.


This patch (of 21):

Rename kasan_slab_free_mempool to kasan_mempool_poison_object.

kasan_slab_free_mempool is a slightly confusing name: it is unclear
whether this function poisons the object when it is freed into mempool or
does something when the object is freed from mempool to the underlying
allocator.

The new name also aligns with other mempool-related KASAN hooks added in
the following patches in this series.

Link: https://lkml.kernel.org/r/cover.1703024586.git.andreyknvl@google.com
Link: https://lkml.kernel.org/r/c5618685abb7cdbf9fb4897f565e7759f601da84.1703024586.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

All callers are passing end_buffer_async_write as this argument, so we can
hardcode references to it within __block_write_full_folio().  That lets us
make end_buffer_async_write() static.

Link: https://lkml.kernel.org/r/20231215200245.748418-15-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Convert the function to be compatible with writepage_t so that it can be
passed to write_cache_pages() by blkdev.  This removes a call to
compound_head().  We can also remove the function export as both callers
are built-in.

Link: https://lkml.kernel.org/r/20231215200245.748418-14-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

If the filesystem implements migrate_folio and writepages, there is no
need for a writepage implementation.

Link: https://lkml.kernel.org/r/20231215200245.748418-13-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

If the filesystem implements migrate_folio and writepages, there is no
need for a writepage implementation.

Link: https://lkml.kernel.org/r/20231215200245.748418-12-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

If the filesystem implements migrate_folio and writepages, there is no
need for a writepage implementation.

Link: https://lkml.kernel.org/r/20231215200245.748418-11-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

If the filesystem implements migrate_folio and writepages, there is no
need for a writepage implementation.

Link: https://lkml.kernel.org/r/20231215200245.748418-10-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

The earlier commit to remove hfsplus_writepage only removed it from one of
the aops.  Remove it from the btree_aops as well.

Link: https://lkml.kernel.org/r/20231215200245.748418-9-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

The earlier commit to remove hfs_writepage only removed it from one of the
aops.  Remove it from the btree_aops as well.

Link: https://lkml.kernel.org/r/20231215200245.748418-8-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

If the filesystem implements migrate_folio and writepages, there is no
need for a writepage implementation.

Link: https://lkml.kernel.org/r/20231215200245.748418-7-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

If the filesystem implements migrate_folio and writepages, there is no
need for a writepage implementation.

Link: https://lkml.kernel.org/r/20231215200245.748418-6-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Some architectures support a very large PAGE_SIZE, so instead of the 8
pointers we see with a 4kB PAGE_SIZE, we can see 128 pointers with 64kB or
so many on Hexagon that it trips compiler warnings about exceeding stack
frame size.

All we're doing with this array is checking for block contiguity, which we
can as well do by remembering the address of the first block in the page
and checking this block is at the appropriate offset from that address.

Link: https://lkml.kernel.org/r/20231215200245.748418-5-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Some architectures support a very large PAGE_SIZE, so instead of the 8
pointers we see with a 4kB PAGE_SIZE, we can see 128 pointers with 64kB or
so many on Hexagon that it trips compiler warnings about exceeding stack
frame size.

All we're doing with this array is checking for block contiguity, which we
can as well do by remembering the address of the first block in the page
and checking this block is at the appropriate offset from that address.

Link: https://lkml.kernel.org/r/20231215200245.748418-4-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

The only caller already has a folio, so pass it in and use it throughout. 
Saves two calls to compound_head().

Link: https://lkml.kernel.org/r/20231215200245.748418-3-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Patch series "Clean up the writeback paths".

Most of these patches verge on the trivial, converting filesystems that
just use block_write_full_page() to use mpage_writepages().  But as we saw
with Christoph's earlier patchset, there can be some "interesting"
gotchas, and I clearly haven't tested the majority of filesystems I've
touched here.

Patches 3 & 4 get rid of a lot of stack usage on architectures with larger
page sizes; 1024 bytes on 64-bit systems with 64KiB pages.  It starts to
open the door to larger folio sizes on all architectures, but it's
certainly not enough yet.

Patch 14 is kind of trivial, but it's nice to get that simplification in.


This patch (of 14):

This function has been unused since the removal of bdev_write_page().

Link: https://lkml.kernel.org/r/20231215200245.748418-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20231215200245.748418-2-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

When running stress-ng testing, we found below kernel crash after a few hours:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
pc : dentry_name+0xd8/0x224
lr : pointer+0x22c/0x370
sp : ffff800025f134c0
......
Call trace:
  dentry_name+0xd8/0x224
  pointer+0x22c/0x370
  vsnprintf+0x1ec/0x730
  vscnprintf+0x2c/0x60
  vprintk_store+0x70/0x234
  vprintk_emit+0xe0/0x24c
  vprintk_default+0x3c/0x44
  vprintk_func+0x84/0x2d0
  printk+0x64/0x88
  __dump_page+0x52c/0x530
  dump_page+0x14/0x20
  set_migratetype_isolate+0x110/0x224
  start_isolate_page_range+0xc4/0x20c
  offline_pages+0x124/0x474
  memory_block_offline+0x44/0xf4
  memory_subsys_offline+0x3c/0x70
  device_offline+0xf0/0x120
  ......

After analyzing the vmcore, I found this issue is caused by page migration.
The scenario is that, one thread is doing page migration, and we will use the
target page's ->mapping field to save 'anon_vma' pointer between page unmap and
page move, and now the target page is locked and refcount is 1.

Currently, there is another stress-ng thread performing memory hotplug,
attempting to offline the target page that is being migrated. It discovers that
the refcount of this target page is 1, preventing the offline operation, thus
proceeding to dump the page. However, page_mapping() of the target page may
return an incorrect file mapping to crash the system in dump_mapping(), since
the target page->mapping only saves 'anon_vma' pointer without setting
PAGE_MAPPING_ANON flag.

There are seveval ways to fix this issue:
(1) Setting the PAGE_MAPPING_ANON flag for target page's ->mapping when saving
'anon_vma', but this can confuse PageAnon() for PFN walkers, since the target
page has not built mappings yet.
(2) Getting the page lock to call page_mapping() in __dump_page() to avoid crashing
the system, however, there are still some PFN walkers that call page_mapping()
without holding the page lock, such as compaction.
(3) Using target page->private field to save the 'anon_vma' pointer and 2 bits
page state, just as page->mapping records an anonymous page, which can remove
the page_mapping() impact for PFN walkers and also seems a simple way.

So I choose option 3 to fix this issue, and this can also fix other potential
issues for PFN walkers, such as compaction.

Link: https://lkml.kernel.org/r/e60b17a88afc38cb32f84c3e30837ec70b343d2b.1702641709.git.baolin.wang@linux.alibaba.com
Fixes: 64c8902e ("migrate_pages: split unmap_and_move() to _unmap() and _move()")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Xu Yu <xuyu@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

shmem_swapin_cluster() immediately converts the page back to a folio, and
swapin_readahead() may as well call folio_file_page() once instead of
having each function call it.

[willy@infradead.org: avoid NULL pointer deref]
  Link: https://lkml.kernel.org/r/ZYI7OcVlM1voKfBl@casper.infradead.org
Link: https://lkml.kernel.org/r/20231213215842.671461-14-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

The only two callers simply call put_page() on the page returned, so
they're happier calling folio_put().  Saves two calls to compound_head().

Link: https://lkml.kernel.org/r/20231213215842.671461-13-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

It's more efficient to get the swap_info_struct by calling
swp_swap_info() directly.

Link: https://lkml.kernel.org/r/20231213215842.671461-12-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

All callers have a folio, so pass it in, saving two calls to
compound_head().

Link: https://lkml.kernel.org/r/20231213215842.671461-11-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

All callers have a folio, so pass it in.  Saves a couple of calls to
compound_head().

Link: https://lkml.kernel.org/r/20231213215842.671461-10-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Make it plain that this takes the head page (which before this point
was just an assumption, but is now enforced by the compiler).

Link: https://lkml.kernel.org/r/20231213215842.671461-9-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Make it plain that this takes the head page (which before this point
was just an assumption, but is now enforced by the compiler).

Link: https://lkml.kernel.org/r/20231213215842.671461-8-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves a call to compound_head().

Link: https://lkml.kernel.org/r/20231213215842.671461-7-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves a call to compound_head().

Link: https://lkml.kernel.org/r/20231213215842.671461-6-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Saves a call to compound_head().

Link: https://lkml.kernel.org/r/20231213215842.671461-5-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>