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, 290 insertions, 0 deletions

diff --git a/fs/ntfs/bitmap.c b/fs/ntfs/bitmap.c
new file mode 100644
index 000000000..b1436b315
--- /dev/null
+++ b/fs/ntfs/bitmap.c
@@ -0,0 +1,290 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * NTFS kernel bitmap handling.
+ *
+ * Copyright (c) 2004-2005 Anton Altaparmakov
+ * Copyright (c) 2025 LG Electronics Co., Ltd.
+ */
+
+#include <linux/bitops.h>
+#include <linux/blkdev.h>
+
+#include "bitmap.h"
+#include "ntfs.h"
+
+int ntfs_trim_fs(struct ntfs_volume *vol, struct fstrim_range *range)
+{
+	size_t buf_clusters;
+	pgoff_t index, start_index, end_index;
+	struct file_ra_state *ra;
+	struct folio *folio;
+	unsigned long *bitmap;
+	char *kaddr;
+	u64 end, trimmed = 0, start_buf, end_buf, end_cluster;
+	u64 start_cluster = ntfs_bytes_to_cluster(vol, range->start);
+	u32 dq = bdev_discard_granularity(vol->sb->s_bdev);
+	int ret = 0;
+
+	if (!dq)
+		dq = vol->cluster_size;
+
+	if (start_cluster >= vol->nr_clusters)
+		return -EINVAL;
+
+	if (range->len == (u64)-1)
+		end_cluster = vol->nr_clusters;
+	else {
+		end_cluster = ntfs_bytes_to_cluster(vol,
+				(range->start + range->len + vol->cluster_size - 1));
+		if (end_cluster > vol->nr_clusters)
+			end_cluster = vol->nr_clusters;
+	}
+
+	ra = kzalloc(sizeof(*ra), GFP_NOFS);
+	if (!ra)
+		return -ENOMEM;
+
+	buf_clusters = PAGE_SIZE * 8;
+	start_index = start_cluster >> 15;
+	end_index = (end_cluster + buf_clusters - 1) >> 15;
+
+	for (index = start_index; index < end_index; index++) {
+		folio = ntfs_get_locked_folio(vol->lcnbmp_ino->i_mapping,
+				index, end_index, ra);
+		if (IS_ERR(folio)) {
+			ret = PTR_ERR(folio);
+			goto out_free;
+		}
+
+		kaddr = kmap_local_folio(folio, 0);
+		bitmap = (unsigned long *)kaddr;
+
+		start_buf = max_t(u64, index * buf_clusters, start_cluster);
+		end_buf = min_t(u64, (index + 1) * buf_clusters, end_cluster);
+
+		end = start_buf;
+		while (end < end_buf) {
+			u64 aligned_start, aligned_count;
+			u64 start = find_next_zero_bit(bitmap, end_buf - start_buf,
+					end - start_buf) + start_buf;
+			if (start >= end_buf)
+				break;
+
+			end = find_next_bit(bitmap, end_buf - start_buf,
+					start - start_buf) + start_buf;
+
+			aligned_start = ALIGN(ntfs_cluster_to_bytes(vol, start), dq);
+			aligned_count =
+				ALIGN_DOWN(ntfs_cluster_to_bytes(vol, end - start), dq);
+			if (aligned_count >= range->minlen) {
+				ret = blkdev_issue_discard(vol->sb->s_bdev, aligned_start >> 9,
+						aligned_count >> 9, GFP_NOFS);
+				if (ret)
+					goto out_unmap;
+				trimmed += aligned_count;
+			}
+		}
+
+out_unmap:
+		kunmap_local(kaddr);
+		folio_unlock(folio);
+		folio_put(folio);
+
+		if (ret)
+			goto out_free;
+	}
+
+	range->len = trimmed;
+
+out_free:
+	kfree(ra);
+	return ret;
+}
+
+/*
+ * __ntfs_bitmap_set_bits_in_run - set a run of bits in a bitmap to a value
+ * @vi:			vfs inode describing the bitmap
+ * @start_bit:		first bit to set
+ * @count:		number of bits to set
+ * @value:		value to set the bits to (i.e. 0 or 1)
+ * @is_rollback:	if 'true' this is a rollback operation
+ *
+ * Set @count bits starting at bit @start_bit in the bitmap described by the
+ * vfs inode @vi to @value, where @value is either 0 or 1.
+ *
+ * @is_rollback should always be 'false', it is for internal use to rollback
+ * errors.  You probably want to use ntfs_bitmap_set_bits_in_run() instead.
+ *
+ * Return 0 on success and -errno on error.
+ */
+int __ntfs_bitmap_set_bits_in_run(struct inode *vi, const s64 start_bit,
+		const s64 count, const u8 value, const bool is_rollback)
+{
+	s64 cnt = count;
+	pgoff_t index, end_index;
+	struct address_space *mapping;
+	struct folio *folio;
+	u8 *kaddr;
+	int pos, len, err;
+	u8 bit;
+	struct ntfs_inode *ni = NTFS_I(vi);
+	struct ntfs_volume *vol = ni->vol;
+
+	ntfs_debug("Entering for i_ino 0x%llx, start_bit 0x%llx, count 0x%llx, value %u.%s",
+			ni->mft_no, (unsigned long long)start_bit,
+			(unsigned long long)cnt, (unsigned int)value,
+			is_rollback ? " (rollback)" : "");
+
+	if (start_bit < 0 || cnt < 0 || value > 1)
+		return -EINVAL;
+
+	/*
+	 * Calculate the indices for the pages containing the first and last
+	 * bits, i.e. @start_bit and @start_bit + @cnt - 1, respectively.
+	 */
+	index = start_bit >> (3 + PAGE_SHIFT);
+	end_index = (start_bit + cnt - 1) >> (3 + PAGE_SHIFT);
+
+	/* Get the page containing the first bit (@start_bit). */
+	mapping = vi->i_mapping;
+	folio = read_mapping_folio(mapping, index, NULL);
+	if (IS_ERR(folio)) {
+		if (!is_rollback)
+			ntfs_error(vi->i_sb,
+				"Failed to map first page (error %li), aborting.",
+				PTR_ERR(folio));
+		return PTR_ERR(folio);
+	}
+
+	folio_lock(folio);
+	kaddr = kmap_local_folio(folio, 0);
+
+	/* Set @pos to the position of the byte containing @start_bit. */
+	pos = (start_bit >> 3) & ~PAGE_MASK;
+
+	/* Calculate the position of @start_bit in the first byte. */
+	bit = start_bit & 7;
+
+	/* If the first byte is partial, modify the appropriate bits in it. */
+	if (bit) {
+		u8 *byte = kaddr + pos;
+
+		if (ni->mft_no == FILE_Bitmap)
+			ntfs_set_lcn_empty_bits(vol, index, value, min_t(s64, 8 - bit, cnt));
+		while ((bit & 7) && cnt) {
+			cnt--;
+			if (value)
+				*byte |= 1 << bit++;
+			else
+				*byte &= ~(1 << bit++);
+		}
+		/* If we are done, unmap the page and return success. */
+		if (!cnt)
+			goto done;
+
+		/* Update @pos to the new position. */
+		pos++;
+	}
+	/*
+	 * Depending on @value, modify all remaining whole bytes in the page up
+	 * to @cnt.
+	 */
+	len = min_t(s64, cnt >> 3, PAGE_SIZE - pos);
+	memset(kaddr + pos, value ? 0xff : 0, len);
+	cnt -= len << 3;
+	if (ni->mft_no == FILE_Bitmap)
+		ntfs_set_lcn_empty_bits(vol, index, value, len << 3);
+
+	/* Update @len to point to the first not-done byte in the page. */
+	if (cnt < 8)
+		len += pos;
+
+	/* If we are not in the last page, deal with all subsequent pages. */
+	while (index < end_index) {
+		if (cnt <= 0) {
+			err = -EIO;
+			goto rollback;
+		}
+
+		/* Update @index and get the next folio. */
+		folio_mark_dirty(folio);
+		folio_unlock(folio);
+		kunmap_local(kaddr);
+		folio_put(folio);
+		folio = read_mapping_folio(mapping, ++index, NULL);
+		if (IS_ERR(folio)) {
+			ntfs_error(vi->i_sb,
+				   "Failed to map subsequent page (error %li), aborting.",
+				   PTR_ERR(folio));
+			err = PTR_ERR(folio);
+			goto rollback;
+		}
+
+		folio_lock(folio);
+		kaddr = kmap_local_folio(folio, 0);
+		/*
+		 * Depending on @value, modify all remaining whole bytes in the
+		 * page up to @cnt.
+		 */
+		len = min_t(s64, cnt >> 3, PAGE_SIZE);
+		memset(kaddr, value ? 0xff : 0, len);
+		cnt -= len << 3;
+		if (ni->mft_no == FILE_Bitmap)
+			ntfs_set_lcn_empty_bits(vol, index, value, len << 3);
+	}
+	/*
+	 * The currently mapped page is the last one.  If the last byte is
+	 * partial, modify the appropriate bits in it.  Note, @len is the
+	 * position of the last byte inside the page.
+	 */
+	if (cnt) {
+		u8 *byte;
+
+		WARN_ON(cnt > 7);
+
+		bit = cnt;
+		byte = kaddr + len;
+		if (ni->mft_no == FILE_Bitmap)
+			ntfs_set_lcn_empty_bits(vol, index, value, bit);
+		while (bit--) {
+			if (value)
+				*byte |= 1 << bit;
+			else
+				*byte &= ~(1 << bit);
+		}
+	}
+done:
+	/* We are done.  Unmap the folio and return success. */
+	folio_mark_dirty(folio);
+	folio_unlock(folio);
+	kunmap_local(kaddr);
+	folio_put(folio);
+	ntfs_debug("Done.");
+	return 0;
+rollback:
+	/*
+	 * Current state:
+	 *	- no pages are mapped
+	 *	- @count - @cnt is the number of bits that have been modified
+	 */
+	if (is_rollback)
+		return err;
+	if (count != cnt)
+		pos = __ntfs_bitmap_set_bits_in_run(vi, start_bit, count - cnt,
+				value ? 0 : 1, true);
+	else
+		pos = 0;
+	if (!pos) {
+		/* Rollback was successful. */
+		ntfs_error(vi->i_sb,
+			"Failed to map subsequent page (error %i), aborting.",
+			err);
+	} else {
+		/* Rollback failed. */
+		ntfs_error(vi->i_sb,
+			"Failed to map subsequent page (error %i) and rollback failed (error %i). Aborting and leaving inconsistent metadata. Unmount and run chkdsk.",
+			err, pos);
+		NVolSetErrors(NTFS_SB(vi->i_sb));
+	}
+	return err;
+}