sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 386 insertions, 0 deletions

diff --git a/fs/squashfs/block.c b/fs/squashfs/block.c
new file mode 100644
index 000000000..2d5850168
--- /dev/null
+++ b/fs/squashfs/block.c
@@ -0,0 +1,386 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Squashfs - a compressed read only filesystem for Linux
+ *
+ * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
+ * Phillip Lougher <phillip@squashfs.org.uk>
+ *
+ * block.c
+ */
+
+/*
+ * This file implements the low-level routines to read and decompress
+ * datablocks and metadata blocks.
+ */
+
+#include <linux/blkdev.h>
+#include <linux/fs.h>
+#include <linux/vfs.h>
+#include <linux/slab.h>
+#include <linux/pagemap.h>
+#include <linux/string.h>
+#include <linux/bio.h>
+
+#include "squashfs_fs.h"
+#include "squashfs_fs_sb.h"
+#include "squashfs.h"
+#include "decompressor.h"
+#include "page_actor.h"
+
+/*
+ * Returns the amount of bytes copied to the page actor.
+ */
+static int copy_bio_to_actor(struct bio *bio,
+			     struct squashfs_page_actor *actor,
+			     int offset, int req_length)
+{
+	void *actor_addr;
+	struct bvec_iter_all iter_all = {};
+	struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
+	int copied_bytes = 0;
+	int actor_offset = 0;
+
+	squashfs_actor_nobuff(actor);
+	actor_addr = squashfs_first_page(actor);
+
+	if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all)))
+		return 0;
+
+	while (copied_bytes < req_length) {
+		int bytes_to_copy = min_t(int, bvec->bv_len - offset,
+					  PAGE_SIZE - actor_offset);
+
+		bytes_to_copy = min_t(int, bytes_to_copy,
+				      req_length - copied_bytes);
+		if (!IS_ERR(actor_addr))
+			memcpy(actor_addr + actor_offset, bvec_virt(bvec) +
+					offset, bytes_to_copy);
+
+		actor_offset += bytes_to_copy;
+		copied_bytes += bytes_to_copy;
+		offset += bytes_to_copy;
+
+		if (actor_offset >= PAGE_SIZE) {
+			actor_addr = squashfs_next_page(actor);
+			if (!actor_addr)
+				break;
+			actor_offset = 0;
+		}
+		if (offset >= bvec->bv_len) {
+			if (!bio_next_segment(bio, &iter_all))
+				break;
+			offset = 0;
+		}
+	}
+	squashfs_finish_page(actor);
+	return copied_bytes;
+}
+
+static int squashfs_bio_read_cached(struct bio *fullbio,
+		struct address_space *cache_mapping, u64 index, int length,
+		u64 read_start, u64 read_end, int page_count)
+{
+	struct folio *head_to_cache = NULL, *tail_to_cache = NULL;
+	struct block_device *bdev = fullbio->bi_bdev;
+	int start_idx = 0, end_idx = 0;
+	struct folio_iter fi;
+	struct bio *bio = NULL;
+	int idx = 0;
+	int err = 0;
+#ifdef CONFIG_SQUASHFS_COMP_CACHE_FULL
+	struct folio **cache_folios = kmalloc_objs(*cache_folios, page_count,
+						   GFP_KERNEL | __GFP_ZERO);
+#endif
+
+	bio_for_each_folio_all(fi, fullbio) {
+		struct folio *folio = fi.folio;
+
+		if (folio->mapping == cache_mapping) {
+			idx++;
+			continue;
+		}
+
+		/*
+		 * We only use this when the device block size is the same as
+		 * the page size, so read_start and read_end cover full pages.
+		 *
+		 * Compare these to the original required index and length to
+		 * only cache pages which were requested partially, since these
+		 * are the ones which are likely to be needed when reading
+		 * adjacent blocks.
+		 */
+		if (idx == 0 && index != read_start)
+			head_to_cache = folio;
+		else if (idx == page_count - 1 && index + length != read_end)
+			tail_to_cache = folio;
+#ifdef CONFIG_SQUASHFS_COMP_CACHE_FULL
+		/* Cache all pages in the BIO for repeated reads */
+		else if (cache_folios)
+			cache_folios[idx] = folio;
+#endif
+
+		if (!bio || idx != end_idx) {
+			struct bio *new = bio_alloc_clone(bdev, fullbio,
+							  GFP_NOIO, &fs_bio_set);
+
+			if (bio) {
+				bio_trim(bio, start_idx * PAGE_SECTORS,
+					 (end_idx - start_idx) * PAGE_SECTORS);
+				bio_chain(bio, new);
+				submit_bio(bio);
+			}
+
+			bio = new;
+			start_idx = idx;
+		}
+
+		idx++;
+		end_idx = idx;
+	}
+
+	if (bio) {
+		bio_trim(bio, start_idx * PAGE_SECTORS,
+			 (end_idx - start_idx) * PAGE_SECTORS);
+		err = submit_bio_wait(bio);
+		bio_put(bio);
+	}
+
+	if (err)
+		return err;
+
+	if (head_to_cache) {
+		int ret = filemap_add_folio(cache_mapping, head_to_cache,
+						read_start >> PAGE_SHIFT,
+						GFP_NOIO);
+
+		if (!ret) {
+			folio_mark_uptodate(head_to_cache);
+			folio_unlock(head_to_cache);
+		}
+
+	}
+
+	if (tail_to_cache) {
+		int ret = filemap_add_folio(cache_mapping, tail_to_cache,
+						(read_end >> PAGE_SHIFT) - 1,
+						GFP_NOIO);
+
+		if (!ret) {
+			folio_mark_uptodate(tail_to_cache);
+			folio_unlock(tail_to_cache);
+		}
+	}
+
+#ifdef CONFIG_SQUASHFS_COMP_CACHE_FULL
+	if (!cache_folios)
+		goto out;
+
+	for (idx = 0; idx < page_count; idx++) {
+		if (!cache_folios[idx])
+			continue;
+		int ret = filemap_add_folio(cache_mapping, cache_folios[idx],
+						(read_start >> PAGE_SHIFT) + idx,
+						GFP_NOIO);
+
+		if (!ret) {
+			folio_mark_uptodate(cache_folios[idx]);
+			folio_unlock(cache_folios[idx]);
+		}
+	}
+	kfree(cache_folios);
+out:
+#endif
+	return 0;
+}
+
+static struct page *squashfs_get_cache_page(struct address_space *mapping,
+					    pgoff_t index)
+{
+	struct page *page;
+
+	if (!mapping)
+		return NULL;
+
+	page = find_get_page(mapping, index);
+	if (!page)
+		return NULL;
+
+	if (!PageUptodate(page)) {
+		put_page(page);
+		return NULL;
+	}
+
+	return page;
+}
+
+static int squashfs_bio_read(struct super_block *sb, u64 index, int length,
+			     struct bio **biop, int *block_offset)
+{
+	struct squashfs_sb_info *msblk = sb->s_fs_info;
+	struct address_space *cache_mapping = msblk->cache_mapping;
+	const u64 read_start = round_down(index, msblk->devblksize);
+	const sector_t block = read_start >> msblk->devblksize_log2;
+	const u64 read_end = round_up(index + length, msblk->devblksize);
+	const sector_t block_end = read_end >> msblk->devblksize_log2;
+	int offset = read_start - round_down(index, PAGE_SIZE);
+	int total_len = (block_end - block) << msblk->devblksize_log2;
+	const int page_count = DIV_ROUND_UP(total_len + offset, PAGE_SIZE);
+	int error, i;
+	struct bio *bio;
+
+	bio = bio_kmalloc(page_count, GFP_NOIO);
+	if (!bio)
+		return -ENOMEM;
+	bio_init_inline(bio, sb->s_bdev, page_count, REQ_OP_READ);
+	bio->bi_iter.bi_sector = block * (msblk->devblksize >> SECTOR_SHIFT);
+
+	for (i = 0; i < page_count; ++i) {
+		unsigned int len =
+			min_t(unsigned int, PAGE_SIZE - offset, total_len);
+		pgoff_t index = (read_start >> PAGE_SHIFT) + i;
+		struct page *page;
+
+		page = squashfs_get_cache_page(cache_mapping, index);
+		if (!page)
+			page = alloc_page(GFP_NOIO);
+
+		if (!page) {
+			error = -ENOMEM;
+			goto out_free_bio;
+		}
+
+		/*
+		 * Use the __ version to avoid merging since we need each page
+		 * to be separate when we check for and avoid cached pages.
+		 */
+		__bio_add_page(bio, page, len, offset);
+		offset = 0;
+		total_len -= len;
+	}
+
+	if (cache_mapping)
+		error = squashfs_bio_read_cached(bio, cache_mapping, index,
+						 length, read_start, read_end,
+						 page_count);
+	else
+		error = submit_bio_wait(bio);
+	if (error)
+		goto out_free_bio;
+
+	*biop = bio;
+	*block_offset = index & ((1 << msblk->devblksize_log2) - 1);
+	return 0;
+
+out_free_bio:
+	bio_free_pages(bio);
+	bio_uninit(bio);
+	kfree(bio);
+	return error;
+}
+
+/*
+ * Read and decompress a metadata block or datablock.  Length is non-zero
+ * if a datablock is being read (the size is stored elsewhere in the
+ * filesystem), otherwise the length is obtained from the first two bytes of
+ * the metadata block.  A bit in the length field indicates if the block
+ * is stored uncompressed in the filesystem (usually because compression
+ * generated a larger block - this does occasionally happen with compression
+ * algorithms).
+ */
+int squashfs_read_data(struct super_block *sb, u64 index, int length,
+		       u64 *next_index, struct squashfs_page_actor *output)
+{
+	struct squashfs_sb_info *msblk = sb->s_fs_info;
+	struct bio *bio = NULL;
+	int compressed;
+	int res;
+	int offset;
+
+	if (length) {
+		/*
+		 * Datablock.
+		 */
+		compressed = SQUASHFS_COMPRESSED_BLOCK(length);
+		length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
+		TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
+			index, compressed ? "" : "un", length, output->length);
+	} else {
+		/*
+		 * Metadata block.
+		 */
+		const u8 *data;
+		struct bvec_iter_all iter_all = {};
+		struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
+
+		if (index + 2 > msblk->bytes_used) {
+			res = -EIO;
+			goto out;
+		}
+		res = squashfs_bio_read(sb, index, 2, &bio, &offset);
+		if (res)
+			goto out;
+
+		if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {
+			res = -EIO;
+			goto out_free_bio;
+		}
+		/* Extract the length of the metadata block */
+		data = bvec_virt(bvec);
+		length = data[offset];
+		if (offset < bvec->bv_len - 1) {
+			length |= data[offset + 1] << 8;
+		} else {
+			if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {
+				res = -EIO;
+				goto out_free_bio;
+			}
+			data = bvec_virt(bvec);
+			length |= data[0] << 8;
+		}
+		bio_free_pages(bio);
+		bio_uninit(bio);
+		kfree(bio);
+
+		compressed = SQUASHFS_COMPRESSED(length);
+		length = SQUASHFS_COMPRESSED_SIZE(length);
+		index += 2;
+
+		TRACE("Block @ 0x%llx, %scompressed size %d\n", index - 2,
+		      compressed ? "" : "un", length);
+	}
+	if (length <= 0 || length > output->length ||
+			(index + length) > msblk->bytes_used) {
+		res = -EIO;
+		goto out;
+	}
+
+	if (next_index)
+		*next_index = index + length;
+
+	res = squashfs_bio_read(sb, index, length, &bio, &offset);
+	if (res)
+		goto out;
+
+	if (compressed) {
+		if (!msblk->stream) {
+			res = -EIO;
+			goto out_free_bio;
+		}
+		res = msblk->thread_ops->decompress(msblk, bio, offset, length, output);
+	} else {
+		res = copy_bio_to_actor(bio, output, offset, length);
+	}
+
+out_free_bio:
+	bio_free_pages(bio);
+	bio_uninit(bio);
+	kfree(bio);
+out:
+	if (res < 0) {
+		ERROR("Failed to read block 0x%llx: %d\n", index, res);
+		if (msblk->panic_on_errors)
+			panic("squashfs read failed");
+	}
+
+	return res;
+}