swh:1:snp:c3bf2749e3476071fa748f67b0ffa2fdc5fe49d9
Tip revision: 9cb1fd0efd195590b828b9b865421ad345a4a145 authored by Linus Torvalds on 24 May 2020, 22:32:54 UTC
Linux 5.7-rc7
Linux 5.7-rc7
Tip revision: 9cb1fd0
readpage.c
// SPDX-License-Identifier: GPL-2.0
/*
* linux/fs/ext4/readpage.c
*
* Copyright (C) 2002, Linus Torvalds.
* Copyright (C) 2015, Google, Inc.
*
* This was originally taken from fs/mpage.c
*
* The intent is the ext4_mpage_readpages() function here is intended
* to replace mpage_readpages() in the general case, not just for
* encrypted files. It has some limitations (see below), where it
* will fall back to read_block_full_page(), but these limitations
* should only be hit when page_size != block_size.
*
* This will allow us to attach a callback function to support ext4
* encryption.
*
* If anything unusual happens, such as:
*
* - encountering a page which has buffers
* - encountering a page which has a non-hole after a hole
* - encountering a page with non-contiguous blocks
*
* then this code just gives up and calls the buffer_head-based read function.
* It does handle a page which has holes at the end - that is a common case:
* the end-of-file on blocksize < PAGE_SIZE setups.
*
*/
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/kdev_t.h>
#include <linux/gfp.h>
#include <linux/bio.h>
#include <linux/fs.h>
#include <linux/buffer_head.h>
#include <linux/blkdev.h>
#include <linux/highmem.h>
#include <linux/prefetch.h>
#include <linux/mpage.h>
#include <linux/writeback.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
#include <linux/cleancache.h>
#include "ext4.h"
#define NUM_PREALLOC_POST_READ_CTXS 128
static struct kmem_cache *bio_post_read_ctx_cache;
static mempool_t *bio_post_read_ctx_pool;
/* postprocessing steps for read bios */
enum bio_post_read_step {
STEP_INITIAL = 0,
STEP_DECRYPT,
STEP_VERITY,
STEP_MAX,
};
struct bio_post_read_ctx {
struct bio *bio;
struct work_struct work;
unsigned int cur_step;
unsigned int enabled_steps;
};
static void __read_end_io(struct bio *bio)
{
struct page *page;
struct bio_vec *bv;
struct bvec_iter_all iter_all;
bio_for_each_segment_all(bv, bio, iter_all) {
page = bv->bv_page;
/* PG_error was set if any post_read step failed */
if (bio->bi_status || PageError(page)) {
ClearPageUptodate(page);
/* will re-read again later */
ClearPageError(page);
} else {
SetPageUptodate(page);
}
unlock_page(page);
}
if (bio->bi_private)
mempool_free(bio->bi_private, bio_post_read_ctx_pool);
bio_put(bio);
}
static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
static void decrypt_work(struct work_struct *work)
{
struct bio_post_read_ctx *ctx =
container_of(work, struct bio_post_read_ctx, work);
fscrypt_decrypt_bio(ctx->bio);
bio_post_read_processing(ctx);
}
static void verity_work(struct work_struct *work)
{
struct bio_post_read_ctx *ctx =
container_of(work, struct bio_post_read_ctx, work);
struct bio *bio = ctx->bio;
/*
* fsverity_verify_bio() may call readpages() again, and although verity
* will be disabled for that, decryption may still be needed, causing
* another bio_post_read_ctx to be allocated. So to guarantee that
* mempool_alloc() never deadlocks we must free the current ctx first.
* This is safe because verity is the last post-read step.
*/
BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
mempool_free(ctx, bio_post_read_ctx_pool);
bio->bi_private = NULL;
fsverity_verify_bio(bio);
__read_end_io(bio);
}
static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
{
/*
* We use different work queues for decryption and for verity because
* verity may require reading metadata pages that need decryption, and
* we shouldn't recurse to the same workqueue.
*/
switch (++ctx->cur_step) {
case STEP_DECRYPT:
if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
INIT_WORK(&ctx->work, decrypt_work);
fscrypt_enqueue_decrypt_work(&ctx->work);
return;
}
ctx->cur_step++;
/* fall-through */
case STEP_VERITY:
if (ctx->enabled_steps & (1 << STEP_VERITY)) {
INIT_WORK(&ctx->work, verity_work);
fsverity_enqueue_verify_work(&ctx->work);
return;
}
ctx->cur_step++;
/* fall-through */
default:
__read_end_io(ctx->bio);
}
}
static bool bio_post_read_required(struct bio *bio)
{
return bio->bi_private && !bio->bi_status;
}
/*
* I/O completion handler for multipage BIOs.
*
* The mpage code never puts partial pages into a BIO (except for end-of-file).
* If a page does not map to a contiguous run of blocks then it simply falls
* back to block_read_full_page().
*
* Why is this? If a page's completion depends on a number of different BIOs
* which can complete in any order (or at the same time) then determining the
* status of that page is hard. See end_buffer_async_read() for the details.
* There is no point in duplicating all that complexity.
*/
static void mpage_end_io(struct bio *bio)
{
if (bio_post_read_required(bio)) {
struct bio_post_read_ctx *ctx = bio->bi_private;
ctx->cur_step = STEP_INITIAL;
bio_post_read_processing(ctx);
return;
}
__read_end_io(bio);
}
static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
{
return fsverity_active(inode) &&
idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
}
static void ext4_set_bio_post_read_ctx(struct bio *bio,
const struct inode *inode,
pgoff_t first_idx)
{
unsigned int post_read_steps = 0;
if (IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode))
post_read_steps |= 1 << STEP_DECRYPT;
if (ext4_need_verity(inode, first_idx))
post_read_steps |= 1 << STEP_VERITY;
if (post_read_steps) {
/* Due to the mempool, this never fails. */
struct bio_post_read_ctx *ctx =
mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
ctx->bio = bio;
ctx->enabled_steps = post_read_steps;
bio->bi_private = ctx;
}
}
static inline loff_t ext4_readpage_limit(struct inode *inode)
{
if (IS_ENABLED(CONFIG_FS_VERITY) &&
(IS_VERITY(inode) || ext4_verity_in_progress(inode)))
return inode->i_sb->s_maxbytes;
return i_size_read(inode);
}
int ext4_mpage_readpages(struct address_space *mapping,
struct list_head *pages, struct page *page,
unsigned nr_pages, bool is_readahead)
{
struct bio *bio = NULL;
sector_t last_block_in_bio = 0;
struct inode *inode = mapping->host;
const unsigned blkbits = inode->i_blkbits;
const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
const unsigned blocksize = 1 << blkbits;
sector_t block_in_file;
sector_t last_block;
sector_t last_block_in_file;
sector_t blocks[MAX_BUF_PER_PAGE];
unsigned page_block;
struct block_device *bdev = inode->i_sb->s_bdev;
int length;
unsigned relative_block = 0;
struct ext4_map_blocks map;
map.m_pblk = 0;
map.m_lblk = 0;
map.m_len = 0;
map.m_flags = 0;
for (; nr_pages; nr_pages--) {
int fully_mapped = 1;
unsigned first_hole = blocks_per_page;
if (pages) {
page = lru_to_page(pages);
prefetchw(&page->flags);
list_del(&page->lru);
if (add_to_page_cache_lru(page, mapping, page->index,
readahead_gfp_mask(mapping)))
goto next_page;
}
if (page_has_buffers(page))
goto confused;
block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
last_block = block_in_file + nr_pages * blocks_per_page;
last_block_in_file = (ext4_readpage_limit(inode) +
blocksize - 1) >> blkbits;
if (last_block > last_block_in_file)
last_block = last_block_in_file;
page_block = 0;
/*
* Map blocks using the previous result first.
*/
if ((map.m_flags & EXT4_MAP_MAPPED) &&
block_in_file > map.m_lblk &&
block_in_file < (map.m_lblk + map.m_len)) {
unsigned map_offset = block_in_file - map.m_lblk;
unsigned last = map.m_len - map_offset;
for (relative_block = 0; ; relative_block++) {
if (relative_block == last) {
/* needed? */
map.m_flags &= ~EXT4_MAP_MAPPED;
break;
}
if (page_block == blocks_per_page)
break;
blocks[page_block] = map.m_pblk + map_offset +
relative_block;
page_block++;
block_in_file++;
}
}
/*
* Then do more ext4_map_blocks() calls until we are
* done with this page.
*/
while (page_block < blocks_per_page) {
if (block_in_file < last_block) {
map.m_lblk = block_in_file;
map.m_len = last_block - block_in_file;
if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
set_error_page:
SetPageError(page);
zero_user_segment(page, 0,
PAGE_SIZE);
unlock_page(page);
goto next_page;
}
}
if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
fully_mapped = 0;
if (first_hole == blocks_per_page)
first_hole = page_block;
page_block++;
block_in_file++;
continue;
}
if (first_hole != blocks_per_page)
goto confused; /* hole -> non-hole */
/* Contiguous blocks? */
if (page_block && blocks[page_block-1] != map.m_pblk-1)
goto confused;
for (relative_block = 0; ; relative_block++) {
if (relative_block == map.m_len) {
/* needed? */
map.m_flags &= ~EXT4_MAP_MAPPED;
break;
} else if (page_block == blocks_per_page)
break;
blocks[page_block] = map.m_pblk+relative_block;
page_block++;
block_in_file++;
}
}
if (first_hole != blocks_per_page) {
zero_user_segment(page, first_hole << blkbits,
PAGE_SIZE);
if (first_hole == 0) {
if (ext4_need_verity(inode, page->index) &&
!fsverity_verify_page(page))
goto set_error_page;
SetPageUptodate(page);
unlock_page(page);
goto next_page;
}
} else if (fully_mapped) {
SetPageMappedToDisk(page);
}
if (fully_mapped && blocks_per_page == 1 &&
!PageUptodate(page) && cleancache_get_page(page) == 0) {
SetPageUptodate(page);
goto confused;
}
/*
* This page will go to BIO. Do we need to send this
* BIO off first?
*/
if (bio && (last_block_in_bio != blocks[0] - 1)) {
submit_and_realloc:
submit_bio(bio);
bio = NULL;
}
if (bio == NULL) {
/*
* bio_alloc will _always_ be able to allocate a bio if
* __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
*/
bio = bio_alloc(GFP_KERNEL,
min_t(int, nr_pages, BIO_MAX_PAGES));
ext4_set_bio_post_read_ctx(bio, inode, page->index);
bio_set_dev(bio, bdev);
bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
bio->bi_end_io = mpage_end_io;
bio_set_op_attrs(bio, REQ_OP_READ,
is_readahead ? REQ_RAHEAD : 0);
}
length = first_hole << blkbits;
if (bio_add_page(bio, page, length, 0) < length)
goto submit_and_realloc;
if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
(relative_block == map.m_len)) ||
(first_hole != blocks_per_page)) {
submit_bio(bio);
bio = NULL;
} else
last_block_in_bio = blocks[blocks_per_page - 1];
goto next_page;
confused:
if (bio) {
submit_bio(bio);
bio = NULL;
}
if (!PageUptodate(page))
block_read_full_page(page, ext4_get_block);
else
unlock_page(page);
next_page:
if (pages)
put_page(page);
}
BUG_ON(pages && !list_empty(pages));
if (bio)
submit_bio(bio);
return 0;
}
int __init ext4_init_post_read_processing(void)
{
bio_post_read_ctx_cache =
kmem_cache_create("ext4_bio_post_read_ctx",
sizeof(struct bio_post_read_ctx), 0, 0, NULL);
if (!bio_post_read_ctx_cache)
goto fail;
bio_post_read_ctx_pool =
mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
bio_post_read_ctx_cache);
if (!bio_post_read_ctx_pool)
goto fail_free_cache;
return 0;
fail_free_cache:
kmem_cache_destroy(bio_post_read_ctx_cache);
fail:
return -ENOMEM;
}
void ext4_exit_post_read_processing(void)
{
mempool_destroy(bio_post_read_ctx_pool);
kmem_cache_destroy(bio_post_read_ctx_cache);
}