// SPDX-License-Identifier: GPL-2.0-or-later
/* handling of writes to regular files and writing back to the server
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/backing-dev.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/netfs.h>
#include <linux/fscache.h>
#include "internal.h"

/*
 * mark a page as having been made dirty and thus needing writeback
 */
int afs_set_page_dirty(struct page *page)
{
        _enter("");
        return __set_page_dirty_nobuffers(page);
}

/*
 * prepare to perform part of a write to a page
 */
int afs_write_begin(struct file *file, struct address_space *mapping,
                    loff_t pos, unsigned len, unsigned flags,
                    struct page **_page, void **fsdata)
{
        struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
        struct page *page;
        unsigned long priv;
        unsigned f, from;
        unsigned t, to;
        pgoff_t index;
        int ret;

        _enter("{%llx:%llu},%llx,%x",
               vnode->fid.vid, vnode->fid.vnode, pos, len);

        /* Prefetch area to be written into the cache if we're caching this
         * file.  We need to do this before we get a lock on the page in case
         * there's more than one writer competing for the same cache block.
         */
        ret = netfs_write_begin(file, mapping, pos, len, flags, &page, fsdata,
                                &afs_req_ops, NULL);
        if (ret < 0)
                return ret;

        index = page->index;
        from = pos - index * PAGE_SIZE;
        to = from + len;

try_again:
        /* See if this page is already partially written in a way that we can
         * merge the new write with.
         */
        if (PagePrivate(page)) {
                priv = page_private(page);
                f = afs_page_dirty_from(page, priv);
                t = afs_page_dirty_to(page, priv);
                ASSERTCMP(f, <=, t);

                if (PageWriteback(page)) {
                        trace_afs_page_dirty(vnode, tracepoint_string("alrdy"), page);
                        goto flush_conflicting_write;
                }
                /* If the file is being filled locally, allow inter-write
                 * spaces to be merged into writes.  If it's not, only write
                 * back what the user gives us.
                 */
                if (!test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags) &&
                    (to < f || from > t))
                        goto flush_conflicting_write;
        }

        *_page = page;
        _leave(" = 0");
        return 0;

        /* The previous write and this write aren't adjacent or overlapping, so
         * flush the page out.
         */
flush_conflicting_write:
        _debug("flush conflict");
        ret = write_one_page(page);
        if (ret < 0)
                goto error;

        ret = lock_page_killable(page);
        if (ret < 0)
                goto error;
        goto try_again;

error:
        put_page(page);
        _leave(" = %d", ret);
        return ret;
}

/*
 * finalise part of a write to a page
 */
int afs_write_end(struct file *file, struct address_space *mapping,
                  loff_t pos, unsigned len, unsigned copied,
                  struct page *page, void *fsdata)
{
        struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
        unsigned long priv;
        unsigned int f, from = pos & (thp_size(page) - 1);
        unsigned int t, to = from + copied;
        loff_t i_size, maybe_i_size;

        _enter("{%llx:%llu},{%lx}",
               vnode->fid.vid, vnode->fid.vnode, page->index);

        if (!PageUptodate(page)) {
                if (copied < len) {
                        copied = 0;
                        goto out;
                }

                SetPageUptodate(page);
        }

        if (copied == 0)
                goto out;

        maybe_i_size = pos + copied;

        i_size = i_size_read(&vnode->vfs_inode);
        if (maybe_i_size > i_size) {
                write_seqlock(&vnode->cb_lock);
                i_size = i_size_read(&vnode->vfs_inode);
                if (maybe_i_size > i_size)
                        i_size_write(&vnode->vfs_inode, maybe_i_size);
                write_sequnlock(&vnode->cb_lock);
        }

        if (PagePrivate(page)) {
                priv = page_private(page);
                f = afs_page_dirty_from(page, priv);
                t = afs_page_dirty_to(page, priv);
                if (from < f)
                        f = from;
                if (to > t)
                        t = to;
                priv = afs_page_dirty(page, f, t);
                set_page_private(page, priv);
                trace_afs_page_dirty(vnode, tracepoint_string("dirty+"), page);
        } else {
                priv = afs_page_dirty(page, from, to);
                attach_page_private(page, (void *)priv);
                trace_afs_page_dirty(vnode, tracepoint_string("dirty"), page);
        }

        if (set_page_dirty(page))
                _debug("dirtied %lx", page->index);

out:
        unlock_page(page);
        put_page(page);
        return copied;
}

/*
 * kill all the pages in the given range
 */
static void afs_kill_pages(struct address_space *mapping,
                           loff_t start, loff_t len)
{
        struct afs_vnode *vnode = AFS_FS_I(mapping->host);
        struct pagevec pv;
        unsigned int loop, psize;

        _enter("{%llx:%llu},%llx @%llx",
               vnode->fid.vid, vnode->fid.vnode, len, start);

        pagevec_init(&pv);

        do {
                _debug("kill %llx @%llx", len, start);

                pv.nr = find_get_pages_contig(mapping, start / PAGE_SIZE,
                                              PAGEVEC_SIZE, pv.pages);
                if (pv.nr == 0)
                        break;

                for (loop = 0; loop < pv.nr; loop++) {
                        struct page *page = pv.pages[loop];

                        if (page->index * PAGE_SIZE >= start + len)
                                break;

                        psize = thp_size(page);
                        start += psize;
                        len -= psize;
                        ClearPageUptodate(page);
                        end_page_writeback(page);
                        lock_page(page);
                        generic_error_remove_page(mapping, page);
                        unlock_page(page);
                }

                __pagevec_release(&pv);
        } while (len > 0);

        _leave("");
}

/*
 * Redirty all the pages in a given range.
 */
static void afs_redirty_pages(struct writeback_control *wbc,
                              struct address_space *mapping,
                              loff_t start, loff_t len)
{
        struct afs_vnode *vnode = AFS_FS_I(mapping->host);
        struct pagevec pv;
        unsigned int loop, psize;

        _enter("{%llx:%llu},%llx @%llx",
               vnode->fid.vid, vnode->fid.vnode, len, start);

        pagevec_init(&pv);

        do {
                _debug("redirty %llx @%llx", len, start);

                pv.nr = find_get_pages_contig(mapping, start / PAGE_SIZE,
                                              PAGEVEC_SIZE, pv.pages);
                if (pv.nr == 0)
                        break;

                for (loop = 0; loop < pv.nr; loop++) {
                        struct page *page = pv.pages[loop];

                        if (page->index * PAGE_SIZE >= start + len)
                                break;

                        psize = thp_size(page);
                        start += psize;
                        len -= psize;
                        redirty_page_for_writepage(wbc, page);
                        end_page_writeback(page);
                }

                __pagevec_release(&pv);
        } while (len > 0);

        _leave("");
}

/*
 * completion of write to server
 */
static void afs_pages_written_back(struct afs_vnode *vnode, loff_t start, unsigned int len)
{
        struct address_space *mapping = vnode->vfs_inode.i_mapping;
        struct page *page;
        pgoff_t end;

        XA_STATE(xas, &mapping->i_pages, start / PAGE_SIZE);

        _enter("{%llx:%llu},{%x @%llx}",
               vnode->fid.vid, vnode->fid.vnode, len, start);

        rcu_read_lock();

        end = (start + len - 1) / PAGE_SIZE;
        xas_for_each(&xas, page, end) {
                if (!PageWriteback(page)) {
                        kdebug("bad %x @%llx page %lx %lx", len, start, page->index, end);
                        ASSERT(PageWriteback(page));
                }

                trace_afs_page_dirty(vnode, tracepoint_string("clear"), page);
                detach_page_private(page);
                page_endio(page, true, 0);
        }

        rcu_read_unlock();

        afs_prune_wb_keys(vnode);
        _leave("");
}

/*
 * Find a key to use for the writeback.  We cached the keys used to author the
 * writes on the vnode.  *_wbk will contain the last writeback key used or NULL
 * and we need to start from there if it's set.
 */
static int afs_get_writeback_key(struct afs_vnode *vnode,
                                 struct afs_wb_key **_wbk)
{
        struct afs_wb_key *wbk = NULL;
        struct list_head *p;
        int ret = -ENOKEY, ret2;

        spin_lock(&vnode->wb_lock);
        if (*_wbk)
                p = (*_wbk)->vnode_link.next;
        else
                p = vnode->wb_keys.next;

        while (p != &vnode->wb_keys) {
                wbk = list_entry(p, struct afs_wb_key, vnode_link);
                _debug("wbk %u", key_serial(wbk->key));
                ret2 = key_validate(wbk->key);
                if (ret2 == 0) {
                        refcount_inc(&wbk->usage);
                        _debug("USE WB KEY %u", key_serial(wbk->key));
                        break;
                }

                wbk = NULL;
                if (ret == -ENOKEY)
                        ret = ret2;
                p = p->next;
        }

        spin_unlock(&vnode->wb_lock);
        if (*_wbk)
                afs_put_wb_key(*_wbk);
        *_wbk = wbk;
        return 0;
}

static void afs_store_data_success(struct afs_operation *op)
{
        struct afs_vnode *vnode = op->file[0].vnode;

        op->ctime = op->file[0].scb.status.mtime_client;
        afs_vnode_commit_status(op, &op->file[0]);
        if (op->error == 0) {
                if (!op->store.laundering)
                        afs_pages_written_back(vnode, op->store.pos, op->store.size);
                afs_stat_v(vnode, n_stores);
                atomic_long_add(op->store.size, &afs_v2net(vnode)->n_store_bytes);
        }
}

static const struct afs_operation_ops afs_store_data_operation = {
        .issue_afs_rpc  = afs_fs_store_data,
        .issue_yfs_rpc  = yfs_fs_store_data,
        .success        = afs_store_data_success,
};

/*
 * write to a file
 */
static int afs_store_data(struct afs_vnode *vnode, struct iov_iter *iter, loff_t pos,
                          bool laundering)
{
        struct afs_operation *op;
        struct afs_wb_key *wbk = NULL;
        loff_t size = iov_iter_count(iter), i_size;
        int ret = -ENOKEY;

        _enter("%s{%llx:%llu.%u},%llx,%llx",
               vnode->volume->name,
               vnode->fid.vid,
               vnode->fid.vnode,
               vnode->fid.unique,
               size, pos);

        ret = afs_get_writeback_key(vnode, &wbk);
        if (ret) {
                _leave(" = %d [no keys]", ret);
                return ret;
        }

        op = afs_alloc_operation(wbk->key, vnode->volume);
        if (IS_ERR(op)) {
                afs_put_wb_key(wbk);
                return -ENOMEM;
        }

        i_size = i_size_read(&vnode->vfs_inode);

        afs_op_set_vnode(op, 0, vnode);
        op->file[0].dv_delta = 1;
        op->file[0].modification = true;
        op->store.write_iter = iter;
        op->store.pos = pos;
        op->store.size = size;
        op->store.i_size = max(pos + size, i_size);
        op->store.laundering = laundering;
        op->mtime = vnode->vfs_inode.i_mtime;
        op->flags |= AFS_OPERATION_UNINTR;
        op->ops = &afs_store_data_operation;

try_next_key:
        afs_begin_vnode_operation(op);
        afs_wait_for_operation(op);

        switch (op->error) {
        case -EACCES:
        case -EPERM:
        case -ENOKEY:
        case -EKEYEXPIRED:
        case -EKEYREJECTED:
        case -EKEYREVOKED:
                _debug("next");

                ret = afs_get_writeback_key(vnode, &wbk);
                if (ret == 0) {
                        key_put(op->key);
                        op->key = key_get(wbk->key);
                        goto try_next_key;
                }
                break;
        }

        afs_put_wb_key(wbk);
        _leave(" = %d", op->error);
        return afs_put_operation(op);
}

/*
 * Extend the region to be written back to include subsequent contiguously
 * dirty pages if possible, but don't sleep while doing so.
 *
 * If this page holds new content, then we can include filler zeros in the
 * writeback.
 */
static void afs_extend_writeback(struct address_space *mapping,
                                 struct afs_vnode *vnode,
                                 long *_count,
                                 loff_t start,
                                 loff_t max_len,
                                 bool new_content,
                                 unsigned int *_len)
{
        struct pagevec pvec;
        struct page *page;
        unsigned long priv;
        unsigned int psize, filler = 0;
        unsigned int f, t;
        loff_t len = *_len;
        pgoff_t index = (start + len) / PAGE_SIZE;
        bool stop = true;
        unsigned int i;

        XA_STATE(xas, &mapping->i_pages, index);
        pagevec_init(&pvec);

        do {
                /* Firstly, we gather up a batch of contiguous dirty pages
                 * under the RCU read lock - but we can't clear the dirty flags
                 * there if any of those pages are mapped.
                 */
                rcu_read_lock();

                xas_for_each(&xas, page, ULONG_MAX) {
                        stop = true;
                        if (xas_retry(&xas, page))
                                continue;
                        if (xa_is_value(page))
                                break;
                        if (page->index != index)
                                break;

                        if (!page_cache_get_speculative(page)) {
                                xas_reset(&xas);
                                continue;
                        }

                        /* Has the page moved or been split? */
                        if (unlikely(page != xas_reload(&xas)))
                                break;

                        if (!trylock_page(page))
                                break;
                        if (!PageDirty(page) || PageWriteback(page)) {
                                unlock_page(page);
                                break;
                        }

                        psize = thp_size(page);
                        priv = page_private(page);
                        f = afs_page_dirty_from(page, priv);
                        t = afs_page_dirty_to(page, priv);
                        if (f != 0 && !new_content) {
                                unlock_page(page);
                                break;
                        }

                        len += filler + t;
                        filler = psize - t;
                        if (len >= max_len || *_count <= 0)
                                stop = true;
                        else if (t == psize || new_content)
                                stop = false;

                        index += thp_nr_pages(page);
                        if (!pagevec_add(&pvec, page))
                                break;
                        if (stop)
                                break;
                }

                if (!stop)
                        xas_pause(&xas);
                rcu_read_unlock();

                /* Now, if we obtained any pages, we can shift them to being
                 * writable and mark them for caching.
                 */
                if (!pagevec_count(&pvec))
                        break;

                for (i = 0; i < pagevec_count(&pvec); i++) {
                        page = pvec.pages[i];
                        trace_afs_page_dirty(vnode, tracepoint_string("store+"), page);

                        if (!clear_page_dirty_for_io(page))
                                BUG();
                        if (test_set_page_writeback(page))
                                BUG();

                        *_count -= thp_nr_pages(page);
                        unlock_page(page);
                }

                pagevec_release(&pvec);
                cond_resched();
        } while (!stop);

        *_len = len;
}

/*
 * Synchronously write back the locked page and any subsequent non-locked dirty
 * pages.
 */
static ssize_t afs_write_back_from_locked_page(struct address_space *mapping,
                                               struct writeback_control *wbc,
                                               struct page *page,
                                               loff_t start, loff_t end)
{
        struct afs_vnode *vnode = AFS_FS_I(mapping->host);
        struct iov_iter iter;
        unsigned long priv;
        unsigned int offset, to, len, max_len;
        loff_t i_size = i_size_read(&vnode->vfs_inode);
        bool new_content = test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags);
        long count = wbc->nr_to_write;
        int ret;

        _enter(",%lx,%llx-%llx", page->index, start, end);

        if (test_set_page_writeback(page))
                BUG();

        count -= thp_nr_pages(page);

        /* Find all consecutive lockable dirty pages that have contiguous
         * written regions, stopping when we find a page that is not
         * immediately lockable, is not dirty or is missing, or we reach the
         * end of the range.
         */
        priv = page_private(page);
        offset = afs_page_dirty_from(page, priv);
        to = afs_page_dirty_to(page, priv);
        trace_afs_page_dirty(vnode, tracepoint_string("store"), page);

        len = to - offset;
        start += offset;
        if (start < i_size) {
                /* Trim the write to the EOF; the extra data is ignored.  Also
                 * put an upper limit on the size of a single storedata op.
                 */
                max_len = 65536 * 4096;
                max_len = min_t(unsigned long long, max_len, end - start + 1);
                max_len = min_t(unsigned long long, max_len, i_size - start);

                if (len < max_len &&
                    (to == thp_size(page) || new_content))
                        afs_extend_writeback(mapping, vnode, &count,
                                             start, max_len, new_content, &len);
                len = min_t(loff_t, len, max_len);
        }

        /* We now have a contiguous set of dirty pages, each with writeback
         * set; the first page is still locked at this point, but all the rest
         * have been unlocked.
         */
        unlock_page(page);

        if (start < i_size) {
                _debug("write back %x @%llx [%llx]", len, start, i_size);

                iov_iter_xarray(&iter, WRITE, &mapping->i_pages, start, len);
                ret = afs_store_data(vnode, &iter, start, false);
        } else {
                _debug("write discard %x @%llx [%llx]", len, start, i_size);

                /* The dirty region was entirely beyond the EOF. */
                afs_pages_written_back(vnode, start, len);
                ret = 0;
        }

        switch (ret) {
        case 0:
                wbc->nr_to_write = count;
                ret = len;
                break;

        default:
                pr_notice("kAFS: Unexpected error from FS.StoreData %d\n", ret);
                fallthrough;
        case -EACCES:
        case -EPERM:
        case -ENOKEY:
        case -EKEYEXPIRED:
        case -EKEYREJECTED:
        case -EKEYREVOKED:
                afs_redirty_pages(wbc, mapping, start, len);
                mapping_set_error(mapping, ret);
                break;

        case -EDQUOT:
        case -ENOSPC:
                afs_redirty_pages(wbc, mapping, start, len);
                mapping_set_error(mapping, -ENOSPC);
                break;

        case -EROFS:
        case -EIO:
        case -EREMOTEIO:
        case -EFBIG:
        case -ENOENT:
        case -ENOMEDIUM:
        case -ENXIO:
                trace_afs_file_error(vnode, ret, afs_file_error_writeback_fail);
                afs_kill_pages(mapping, start, len);
                mapping_set_error(mapping, ret);
                break;
        }

        _leave(" = %d", ret);
        return ret;
}

/*
 * write a page back to the server
 * - the caller locked the page for us
 */
int afs_writepage(struct page *page, struct writeback_control *wbc)
{
        ssize_t ret;
        loff_t start;

        _enter("{%lx},", page->index);

        start = page->index * PAGE_SIZE;
        ret = afs_write_back_from_locked_page(page->mapping, wbc, page,
                                              start, LLONG_MAX - start);
        if (ret < 0) {
                _leave(" = %zd", ret);
                return ret;
        }

        _leave(" = 0");
        return 0;
}

/*
 * write a region of pages back to the server
 */
static int afs_writepages_region(struct address_space *mapping,
                                 struct writeback_control *wbc,
                                 loff_t start, loff_t end, loff_t *_next)
{
        struct page *page;
        ssize_t ret;
        int n;

        _enter("%llx,%llx,", start, end);

        do {
                pgoff_t index = start / PAGE_SIZE;

                n = find_get_pages_range_tag(mapping, &index, end / PAGE_SIZE,
                                             PAGECACHE_TAG_DIRTY, 1, &page);
                if (!n)
                        break;

                start = (loff_t)page->index * PAGE_SIZE; /* May regress with THPs */

                _debug("wback %lx", page->index);

                /* At this point we hold neither the i_pages lock nor the
                 * page lock: the page may be truncated or invalidated
                 * (changing page->mapping to NULL), or even swizzled
                 * back from swapper_space to tmpfs file mapping
                 */
                if (wbc->sync_mode != WB_SYNC_NONE) {
                        ret = lock_page_killable(page);
                        if (ret < 0) {
                                put_page(page);
                                return ret;
                        }
                } else {
                        if (!trylock_page(page)) {
                                put_page(page);
                                return 0;
                        }
                }

                if (page->mapping != mapping || !PageDirty(page)) {
                        start += thp_size(page);
                        unlock_page(page);
                        put_page(page);
                        continue;
                }

                if (PageWriteback(page)) {
                        unlock_page(page);
                        if (wbc->sync_mode != WB_SYNC_NONE)
                                wait_on_page_writeback(page);
                        put_page(page);
                        continue;
                }

                if (!clear_page_dirty_for_io(page))
                        BUG();
                ret = afs_write_back_from_locked_page(mapping, wbc, page, start, end);
                put_page(page);
                if (ret < 0) {
                        _leave(" = %zd", ret);
                        return ret;
                }

                start += ret;

                cond_resched();
        } while (wbc->nr_to_write > 0);

        *_next = start;
        _leave(" = 0 [%llx]", *_next);
        return 0;
}

/*
 * write some of the pending data back to the server
 */
int afs_writepages(struct address_space *mapping,
                   struct writeback_control *wbc)
{
        struct afs_vnode *vnode = AFS_FS_I(mapping->host);
        loff_t start, next;
        int ret;

        _enter("");

        /* We have to be careful as we can end up racing with setattr()
         * truncating the pagecache since the caller doesn't take a lock here
         * to prevent it.
         */
        if (wbc->sync_mode == WB_SYNC_ALL)
                down_read(&vnode->validate_lock);
        else if (!down_read_trylock(&vnode->validate_lock))
                return 0;

        if (wbc->range_cyclic) {
                start = mapping->writeback_index * PAGE_SIZE;
                ret = afs_writepages_region(mapping, wbc, start, LLONG_MAX, &next);
                if (ret == 0) {
                        mapping->writeback_index = next / PAGE_SIZE;
                        if (start > 0 && wbc->nr_to_write > 0) {
                                ret = afs_writepages_region(mapping, wbc, 0,
                                                            start, &next);
                                if (ret == 0)
                                        mapping->writeback_index =
                                                next / PAGE_SIZE;
                        }
                }
        } else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
                ret = afs_writepages_region(mapping, wbc, 0, LLONG_MAX, &next);
                if (wbc->nr_to_write > 0 && ret == 0)
                        mapping->writeback_index = next / PAGE_SIZE;
        } else {
                ret = afs_writepages_region(mapping, wbc,
                                            wbc->range_start, wbc->range_end, &next);
        }

        up_read(&vnode->validate_lock);
        _leave(" = %d", ret);
        return ret;
}

/*
 * write to an AFS file
 */
ssize_t afs_file_write(struct kiocb *iocb, struct iov_iter *from)
{
        struct afs_vnode *vnode = AFS_FS_I(file_inode(iocb->ki_filp));
        ssize_t result;
        size_t count = iov_iter_count(from);

        _enter("{%llx:%llu},{%zu},",
               vnode->fid.vid, vnode->fid.vnode, count);

        if (IS_SWAPFILE(&vnode->vfs_inode)) {
                printk(KERN_INFO
                       "AFS: Attempt to write to active swap file!\n");
                return -EBUSY;
        }

        if (!count)
                return 0;

        result = generic_file_write_iter(iocb, from);

        _leave(" = %zd", result);
        return result;
}

/*
 * flush any dirty pages for this process, and check for write errors.
 * - the return status from this call provides a reliable indication of
 *   whether any write errors occurred for this process.
 */
int afs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
{
        struct inode *inode = file_inode(file);
        struct afs_vnode *vnode = AFS_FS_I(inode);

        _enter("{%llx:%llu},{n=%pD},%d",
               vnode->fid.vid, vnode->fid.vnode, file,
               datasync);

        return file_write_and_wait_range(file, start, end);
}

/*
 * notification that a previously read-only page is about to become writable
 * - if it returns an error, the caller will deliver a bus error signal
 */
vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
{
        struct page *page = thp_head(vmf->page);
        struct file *file = vmf->vma->vm_file;
        struct inode *inode = file_inode(file);
        struct afs_vnode *vnode = AFS_FS_I(inode);
        unsigned long priv;
        vm_fault_t ret = VM_FAULT_RETRY;

        _enter("{{%llx:%llu}},{%lx}", vnode->fid.vid, vnode->fid.vnode, page->index);

        sb_start_pagefault(inode->i_sb);

        /* Wait for the page to be written to the cache before we allow it to
         * be modified.  We then assume the entire page will need writing back.
         */
#ifdef CONFIG_AFS_FSCACHE
        if (PageFsCache(page) &&
            wait_on_page_fscache_killable(page) < 0)
                goto out;
#endif

        if (wait_on_page_writeback_killable(page))
                goto out;

        if (lock_page_killable(page) < 0)
                goto out;

        /* We mustn't change page->private until writeback is complete as that
         * details the portion of the page we need to write back and we might
         * need to redirty the page if there's a problem.
         */
        if (wait_on_page_writeback_killable(page) < 0) {
                unlock_page(page);
                goto out;
        }

        priv = afs_page_dirty(page, 0, thp_size(page));
        priv = afs_page_dirty_mmapped(priv);
        if (PagePrivate(page)) {
                set_page_private(page, priv);
                trace_afs_page_dirty(vnode, tracepoint_string("mkwrite+"), page);
        } else {
                attach_page_private(page, (void *)priv);
                trace_afs_page_dirty(vnode, tracepoint_string("mkwrite"), page);
        }
        file_update_time(file);

        ret = VM_FAULT_LOCKED;
out:
        sb_end_pagefault(inode->i_sb);
        return ret;
}

/*
 * Prune the keys cached for writeback.  The caller must hold vnode->wb_lock.
 */
void afs_prune_wb_keys(struct afs_vnode *vnode)
{
        LIST_HEAD(graveyard);
        struct afs_wb_key *wbk, *tmp;

        /* Discard unused keys */
        spin_lock(&vnode->wb_lock);

        if (!mapping_tagged(&vnode->vfs_inode.i_data, PAGECACHE_TAG_WRITEBACK) &&
            !mapping_tagged(&vnode->vfs_inode.i_data, PAGECACHE_TAG_DIRTY)) {
                list_for_each_entry_safe(wbk, tmp, &vnode->wb_keys, vnode_link) {
                        if (refcount_read(&wbk->usage) == 1)
                                list_move(&wbk->vnode_link, &graveyard);
                }
        }

        spin_unlock(&vnode->wb_lock);

        while (!list_empty(&graveyard)) {
                wbk = list_entry(graveyard.next, struct afs_wb_key, vnode_link);
                list_del(&wbk->vnode_link);
                afs_put_wb_key(wbk);
        }
}

/*
 * Clean up a page during invalidation.
 */
int afs_launder_page(struct page *page)
{
        struct address_space *mapping = page->mapping;
        struct afs_vnode *vnode = AFS_FS_I(mapping->host);
        struct iov_iter iter;
        struct bio_vec bv[1];
        unsigned long priv;
        unsigned int f, t;
        int ret = 0;

        _enter("{%lx}", page->index);

        priv = page_private(page);
        if (clear_page_dirty_for_io(page)) {
                f = 0;
                t = thp_size(page);
                if (PagePrivate(page)) {
                        f = afs_page_dirty_from(page, priv);
                        t = afs_page_dirty_to(page, priv);
                }

                bv[0].bv_page = page;
                bv[0].bv_offset = f;
                bv[0].bv_len = t - f;
                iov_iter_bvec(&iter, WRITE, bv, 1, bv[0].bv_len);

                trace_afs_page_dirty(vnode, tracepoint_string("launder"), page);
                ret = afs_store_data(vnode, &iter, (loff_t)page->index * PAGE_SIZE,
                                     true);
        }

        trace_afs_page_dirty(vnode, tracepoint_string("laundered"), page);
        detach_page_private(page);
        wait_on_page_fscache(page);
        return ret;
}