Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 908 insertions, 0 deletions

diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
new file mode 100644
index 000000000..851f6f93a
--- /dev/null
+++ b/fs/netfs/write_issue.c
@@ -0,0 +1,908 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Network filesystem high-level (buffered) writeback.
+ *
+ * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ *
+ * To support network filesystems with local caching, we manage a situation
+ * that can be envisioned like the following:
+ *
+ *               +---+---+-----+-----+---+----------+
+ *    Folios:    |   |   |     |     |   |          |
+ *               +---+---+-----+-----+---+----------+
+ *
+ *                 +------+------+     +----+----+
+ *    Upload:      |      |      |.....|    |    |
+ *  (Stream 0)     +------+------+     +----+----+
+ *
+ *               +------+------+------+------+------+
+ *    Cache:     |      |      |      |      |      |
+ *  (Stream 1)   +------+------+------+------+------+
+ *
+ * Where we have a sequence of folios of varying sizes that we need to overlay
+ * with multiple parallel streams of I/O requests, where the I/O requests in a
+ * stream may also be of various sizes (in cifs, for example, the sizes are
+ * negotiated with the server; in something like ceph, they may represent the
+ * sizes of storage objects).
+ *
+ * The sequence in each stream may contain gaps and noncontiguous subrequests
+ * may be glued together into single vectored write RPCs.
+ */
+
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include "internal.h"
+
+/*
+ * Kill all dirty folios in the event of an unrecoverable error, starting with
+ * a locked folio we've already obtained from writeback_iter().
+ */
+static void netfs_kill_dirty_pages(struct address_space *mapping,
+				   struct writeback_control *wbc,
+				   struct folio *folio)
+{
+	int error = 0;
+
+	do {
+		enum netfs_folio_trace why = netfs_folio_trace_kill;
+		struct netfs_group *group = NULL;
+		struct netfs_folio *finfo = NULL;
+		void *priv;
+
+		priv = folio_detach_private(folio);
+		if (priv) {
+			finfo = __netfs_folio_info(priv);
+			if (finfo) {
+				/* Kill folio from streaming write. */
+				group = finfo->netfs_group;
+				why = netfs_folio_trace_kill_s;
+			} else {
+				group = priv;
+				if (group == NETFS_FOLIO_COPY_TO_CACHE) {
+					/* Kill copy-to-cache folio */
+					why = netfs_folio_trace_kill_cc;
+					group = NULL;
+				} else {
+					/* Kill folio with group */
+					why = netfs_folio_trace_kill_g;
+				}
+			}
+		}
+
+		trace_netfs_folio(folio, why);
+
+		folio_start_writeback(folio);
+		folio_unlock(folio);
+		folio_end_writeback(folio);
+
+		netfs_put_group(group);
+		kfree(finfo);
+
+	} while ((folio = writeback_iter(mapping, wbc, folio, &error)));
+}
+
+/*
+ * Create a write request and set it up appropriately for the origin type.
+ */
+struct netfs_io_request *netfs_create_write_req(struct address_space *mapping,
+						struct file *file,
+						loff_t start,
+						enum netfs_io_origin origin)
+{
+	struct netfs_io_request *wreq;
+	struct netfs_inode *ictx;
+	bool is_cacheable = (origin == NETFS_WRITEBACK ||
+			     origin == NETFS_WRITEBACK_SINGLE ||
+			     origin == NETFS_WRITETHROUGH ||
+			     origin == NETFS_PGPRIV2_COPY_TO_CACHE);
+
+	wreq = netfs_alloc_request(mapping, file, start, 0, origin);
+	if (IS_ERR(wreq))
+		return wreq;
+
+	_enter("R=%x", wreq->debug_id);
+
+	ictx = netfs_inode(wreq->inode);
+	if (is_cacheable)
+		fscache_begin_write_operation(&wreq->cache_resources, netfs_i_cookie(ictx));
+	if (rolling_buffer_init(&wreq->buffer, wreq->debug_id, ITER_SOURCE, wreq->gfp) < 0)
+		goto nomem;
+
+	wreq->cleaned_to = wreq->start;
+
+	wreq->io_streams[0].stream_nr		= 0;
+	wreq->io_streams[0].source		= NETFS_UPLOAD_TO_SERVER;
+	wreq->io_streams[0].prepare_write	= ictx->ops->prepare_write;
+	wreq->io_streams[0].issue_write		= ictx->ops->issue_write;
+	wreq->io_streams[0].collected_to	= start;
+	wreq->io_streams[0].transferred		= 0;
+
+	wreq->io_streams[1].stream_nr		= 1;
+	wreq->io_streams[1].source		= NETFS_WRITE_TO_CACHE;
+	wreq->io_streams[1].collected_to	= start;
+	wreq->io_streams[1].transferred		= 0;
+	if (fscache_resources_valid(&wreq->cache_resources)) {
+		wreq->io_streams[1].avail	= true;
+		wreq->io_streams[1].active	= true;
+		wreq->io_streams[1].prepare_write = wreq->cache_resources.ops->prepare_write_subreq;
+		wreq->io_streams[1].issue_write = wreq->cache_resources.ops->issue_write;
+	}
+
+	return wreq;
+nomem:
+	netfs_put_failed_request(wreq);
+	return ERR_PTR(-ENOMEM);
+}
+
+/**
+ * netfs_prepare_write_failed - Note write preparation failed
+ * @subreq: The subrequest to mark
+ *
+ * Mark a subrequest to note that preparation for write failed.
+ */
+void netfs_prepare_write_failed(struct netfs_io_subrequest *subreq)
+{
+	__set_bit(NETFS_SREQ_FAILED, &subreq->flags);
+	trace_netfs_sreq(subreq, netfs_sreq_trace_prep_failed);
+}
+EXPORT_SYMBOL(netfs_prepare_write_failed);
+
+/*
+ * Prepare a write subrequest.  We need to allocate a new subrequest
+ * if we don't have one.
+ */
+void netfs_prepare_write(struct netfs_io_request *wreq,
+			 struct netfs_io_stream *stream,
+			 loff_t start)
+{
+	struct netfs_io_subrequest *subreq;
+	struct iov_iter *wreq_iter = &wreq->buffer.iter;
+
+	/* Make sure we don't point the iterator at a used-up folio_queue
+	 * struct being used as a placeholder to prevent the queue from
+	 * collapsing.  In such a case, extend the queue.
+	 */
+	if (iov_iter_is_folioq(wreq_iter) &&
+	    wreq_iter->folioq_slot >= folioq_nr_slots(wreq_iter->folioq))
+		rolling_buffer_make_space(&wreq->buffer, wreq->gfp);
+
+	subreq = netfs_alloc_subrequest(wreq);
+	if (!subreq)
+		return;
+	subreq->source		= stream->source;
+	subreq->start		= start;
+	subreq->stream_nr	= stream->stream_nr;
+	subreq->io_iter		= *wreq_iter;
+
+	_enter("R=%x[%x]", wreq->debug_id, subreq->debug_index);
+
+	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
+
+	stream->sreq_max_len	= UINT_MAX;
+	stream->sreq_max_segs	= INT_MAX;
+	switch (stream->source) {
+	case NETFS_UPLOAD_TO_SERVER:
+		netfs_stat(&netfs_n_wh_upload);
+		stream->sreq_max_len = wreq->wsize;
+		break;
+	case NETFS_WRITE_TO_CACHE:
+		netfs_stat(&netfs_n_wh_write);
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		break;
+	}
+
+	if (stream->prepare_write)
+		stream->prepare_write(subreq);
+
+	__set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
+
+	/* We add to the end of the list whilst the collector may be walking
+	 * the list.  The collector only goes nextwards and uses the lock to
+	 * remove entries off of the front.
+	 */
+	spin_lock(&wreq->lock);
+	/* Write IN_PROGRESS before pointer to new subreq */
+	list_add_tail_release(&subreq->rreq_link, &stream->subrequests);
+	if (list_is_first(&subreq->rreq_link, &stream->subrequests)) {
+		if (!stream->active) {
+			stream->collected_to = subreq->start;
+			/* Write list pointers before active flag */
+			smp_store_release(&stream->active, true);
+		}
+	}
+
+	spin_unlock(&wreq->lock);
+
+	stream->construct = subreq;
+}
+
+/*
+ * Set the I/O iterator for the filesystem/cache to use and dispatch the I/O
+ * operation.  The operation may be asynchronous and should call
+ * netfs_write_subrequest_terminated() when complete.
+ */
+static void netfs_do_issue_write(struct netfs_io_stream *stream,
+				 struct netfs_io_subrequest *subreq)
+{
+	struct netfs_io_request *wreq = subreq->rreq;
+
+	_enter("R=%x[%x],%zx", wreq->debug_id, subreq->debug_index, subreq->len);
+
+	if (test_bit(NETFS_SREQ_FAILED, &subreq->flags))
+		return netfs_write_subrequest_terminated(subreq, subreq->error);
+
+	trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
+	stream->issue_write(subreq);
+}
+
+void netfs_reissue_write(struct netfs_io_stream *stream,
+			 struct netfs_io_subrequest *subreq,
+			 struct iov_iter *source)
+{
+	size_t size = subreq->len - subreq->transferred;
+
+	// TODO: Use encrypted buffer
+	subreq->io_iter = *source;
+	iov_iter_advance(source, size);
+	iov_iter_truncate(&subreq->io_iter, size);
+
+	subreq->retry_count++;
+	subreq->error = 0;
+	__clear_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags);
+	__set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
+	netfs_stat(&netfs_n_wh_retry_write_subreq);
+	netfs_do_issue_write(stream, subreq);
+}
+
+void netfs_issue_write(struct netfs_io_request *wreq,
+		       struct netfs_io_stream *stream)
+{
+	struct netfs_io_subrequest *subreq = stream->construct;
+
+	if (!subreq)
+		return;
+	stream->construct = NULL;
+	subreq->io_iter.count = subreq->len;
+	netfs_do_issue_write(stream, subreq);
+}
+
+/*
+ * Add data to the write subrequest, dispatching each as we fill it up or if it
+ * is discontiguous with the previous.  We only fill one part at a time so that
+ * we can avoid overrunning the credits obtained (cifs) and try to parallelise
+ * content-crypto preparation with network writes.
+ */
+size_t netfs_advance_write(struct netfs_io_request *wreq,
+			   struct netfs_io_stream *stream,
+			   loff_t start, size_t len, bool to_eof)
+{
+	struct netfs_io_subrequest *subreq = stream->construct;
+	size_t part;
+
+	if (!stream->avail) {
+		_leave("no write");
+		return len;
+	}
+
+	_enter("R=%x[%x]", wreq->debug_id, subreq ? subreq->debug_index : 0);
+
+	if (subreq && start != subreq->start + subreq->len) {
+		netfs_issue_write(wreq, stream);
+		subreq = NULL;
+	}
+
+	if (!stream->construct)
+		netfs_prepare_write(wreq, stream, start);
+	subreq = stream->construct;
+
+	part = umin(stream->sreq_max_len - subreq->len, len);
+	_debug("part %zx/%zx %zx/%zx", subreq->len, stream->sreq_max_len, part, len);
+	subreq->len += part;
+	subreq->nr_segs++;
+	stream->submit_extendable_to -= part;
+
+	if (subreq->len >= stream->sreq_max_len ||
+	    subreq->nr_segs >= stream->sreq_max_segs ||
+	    to_eof) {
+		netfs_issue_write(wreq, stream);
+		subreq = NULL;
+	}
+
+	return part;
+}
+
+/*
+ * Write some of a pending folio data back to the server.
+ */
+static int netfs_write_folio(struct netfs_io_request *wreq,
+			     struct writeback_control *wbc,
+			     struct folio *folio)
+{
+	struct netfs_io_stream *upload = &wreq->io_streams[0];
+	struct netfs_io_stream *cache  = &wreq->io_streams[1];
+	struct netfs_io_stream *stream;
+	struct netfs_group *fgroup; /* TODO: Use this with ceph */
+	struct netfs_folio *finfo;
+	size_t iter_off = 0;
+	size_t fsize = folio_size(folio), flen = fsize, foff = 0;
+	loff_t fpos = folio_pos(folio), i_size;
+	bool to_eof = false, streamw = false;
+	bool debug = false;
+
+	_enter("");
+
+	if (rolling_buffer_make_space(&wreq->buffer, wreq->gfp) < 0)
+		return -ENOMEM;
+
+	/* netfs_perform_write() may shift i_size around the page or from out
+	 * of the page to beyond it, but cannot move i_size into or through the
+	 * page since we have it locked.
+	 */
+	i_size = i_size_read(wreq->inode);
+
+	if (fpos >= i_size) {
+		/* mmap beyond eof. */
+		_debug("beyond eof");
+		folio_start_writeback(folio);
+		folio_unlock(folio);
+		wreq->nr_group_rel += netfs_folio_written_back(folio);
+		netfs_put_group_many(wreq->group, wreq->nr_group_rel);
+		wreq->nr_group_rel = 0;
+		return 0;
+	}
+
+	if (fpos + fsize > wreq->i_size)
+		wreq->i_size = i_size;
+
+	fgroup = netfs_folio_group(folio);
+	finfo = netfs_folio_info(folio);
+	if (finfo) {
+		foff = finfo->dirty_offset;
+		flen = foff + finfo->dirty_len;
+		streamw = true;
+	}
+
+	if (wreq->origin == NETFS_WRITETHROUGH) {
+		to_eof = false;
+		if (flen > i_size - fpos)
+			flen = i_size - fpos;
+	} else if (flen > i_size - fpos) {
+		flen = i_size - fpos;
+		if (!streamw)
+			folio_zero_segment(folio, flen, fsize);
+		to_eof = true;
+	} else if (flen == i_size - fpos) {
+		to_eof = true;
+	}
+	flen -= foff;
+
+	_debug("folio %zx %zx %zx", foff, flen, fsize);
+
+	/* Deal with discontinuities in the stream of dirty pages.  These can
+	 * arise from a number of sources:
+	 *
+	 * (1) Intervening non-dirty pages from random-access writes, multiple
+	 *     flushers writing back different parts simultaneously and manual
+	 *     syncing.
+	 *
+	 * (2) Partially-written pages from write-streaming.
+	 *
+	 * (3) Pages that belong to a different write-back group (eg.  Ceph
+	 *     snapshots).
+	 *
+	 * (4) Actually-clean pages that were marked for write to the cache
+	 *     when they were read.  Note that these appear as a special
+	 *     write-back group.
+	 */
+	if (fgroup == NETFS_FOLIO_COPY_TO_CACHE) {
+		netfs_issue_write(wreq, upload);
+	} else if (fgroup != wreq->group) {
+		/* We can't write this page to the server yet. */
+		kdebug("wrong group");
+		folio_redirty_for_writepage(wbc, folio);
+		folio_unlock(folio);
+		netfs_issue_write(wreq, upload);
+		netfs_issue_write(wreq, cache);
+		return 0;
+	}
+
+	if (foff > 0)
+		netfs_issue_write(wreq, upload);
+	if (streamw)
+		netfs_issue_write(wreq, cache);
+
+	folio_start_writeback(folio);
+	folio_unlock(folio);
+
+	if (fgroup == NETFS_FOLIO_COPY_TO_CACHE) {
+		if (!cache->avail) {
+			trace_netfs_folio(folio, netfs_folio_trace_cancel_copy);
+			netfs_issue_write(wreq, upload);
+			netfs_folio_written_back(folio);
+			return 0;
+		}
+		trace_netfs_folio(folio, netfs_folio_trace_store_copy);
+	} else if (!upload->avail && !cache->avail) {
+		trace_netfs_folio(folio, netfs_folio_trace_cancel_store);
+		netfs_folio_written_back(folio);
+		return 0;
+	} else if (!upload->construct) {
+		trace_netfs_folio(folio, netfs_folio_trace_store);
+	} else {
+		trace_netfs_folio(folio, netfs_folio_trace_store_plus);
+	}
+
+	/* Attach the folio to the rolling buffer. */
+	rolling_buffer_append(&wreq->buffer, folio, 0, wreq->gfp);
+
+	/* Move the submission point forward to allow for write-streaming data
+	 * not starting at the front of the page.  We don't do write-streaming
+	 * with the cache as the cache requires DIO alignment.
+	 *
+	 * Also skip uploading for data that's been read and just needs copying
+	 * to the cache.
+	 */
+	for (int s = 0; s < NR_IO_STREAMS; s++) {
+		stream = &wreq->io_streams[s];
+		stream->submit_off = foff;
+		stream->submit_len = flen;
+		if (!stream->avail ||
+		    (stream->source == NETFS_WRITE_TO_CACHE && streamw) ||
+		    (stream->source == NETFS_UPLOAD_TO_SERVER &&
+		     fgroup == NETFS_FOLIO_COPY_TO_CACHE)) {
+			stream->submit_off = UINT_MAX;
+			stream->submit_len = 0;
+		}
+	}
+
+	/* Attach the folio to one or more subrequests.  For a big folio, we
+	 * could end up with thousands of subrequests if the wsize is small -
+	 * but we might need to wait during the creation of subrequests for
+	 * network resources (eg. SMB credits).
+	 */
+	for (;;) {
+		ssize_t part;
+		size_t lowest_off = ULONG_MAX;
+		int choose_s = -1;
+
+		/* Always add to the lowest-submitted stream first. */
+		for (int s = 0; s < NR_IO_STREAMS; s++) {
+			stream = &wreq->io_streams[s];
+			if (stream->submit_len > 0 &&
+			    stream->submit_off < lowest_off) {
+				lowest_off = stream->submit_off;
+				choose_s = s;
+			}
+		}
+
+		if (choose_s < 0)
+			break;
+		stream = &wreq->io_streams[choose_s];
+
+		/* Advance the iterator(s). */
+		if (stream->submit_off > iter_off) {
+			rolling_buffer_advance(&wreq->buffer, stream->submit_off - iter_off);
+			iter_off = stream->submit_off;
+		}
+
+		atomic64_set(&wreq->issued_to, fpos + stream->submit_off);
+		stream->submit_extendable_to = fsize - stream->submit_off;
+		part = netfs_advance_write(wreq, stream, fpos + stream->submit_off,
+					   stream->submit_len, to_eof);
+		stream->submit_off += part;
+		if (part > stream->submit_len)
+			stream->submit_len = 0;
+		else
+			stream->submit_len -= part;
+		if (part > 0)
+			debug = true;
+	}
+
+	if (fsize > iter_off)
+		rolling_buffer_advance(&wreq->buffer, fsize - iter_off);
+	atomic64_set(&wreq->issued_to, fpos + fsize);
+
+	if (!debug)
+		kdebug("R=%x: No submit", wreq->debug_id);
+
+	if (foff + flen < fsize)
+		for (int s = 0; s < NR_IO_STREAMS; s++)
+			netfs_issue_write(wreq, &wreq->io_streams[s]);
+
+	_leave(" = 0");
+	return 0;
+}
+
+/*
+ * End the issuing of writes, letting the collector know we're done.
+ */
+static void netfs_end_issue_write(struct netfs_io_request *wreq)
+{
+	bool needs_poke = true;
+
+	smp_wmb(); /* Write subreq lists before ALL_QUEUED. */
+	set_bit(NETFS_RREQ_ALL_QUEUED, &wreq->flags);
+
+	for (int s = 0; s < NR_IO_STREAMS; s++) {
+		struct netfs_io_stream *stream = &wreq->io_streams[s];
+
+		if (!stream->active)
+			continue;
+		if (!list_empty(&stream->subrequests))
+			needs_poke = false;
+		netfs_issue_write(wreq, stream);
+	}
+
+	if (needs_poke)
+		netfs_wake_collector(wreq);
+}
+
+/*
+ * Write some of the pending data back to the server
+ */
+int netfs_writepages(struct address_space *mapping,
+		     struct writeback_control *wbc)
+{
+	struct netfs_inode *ictx = netfs_inode(mapping->host);
+	struct netfs_io_request *wreq = NULL;
+	struct folio *folio;
+	int error = 0;
+
+	if (!netfs_wb_begin(ictx, wbc->sync_mode == WB_SYNC_NONE))
+		return 0;
+
+	/* Need the first folio to be able to set up the op. */
+	folio = writeback_iter(mapping, wbc, NULL, &error);
+	if (!folio)
+		goto out;
+
+	wreq = netfs_create_write_req(mapping, NULL, folio_pos(folio), NETFS_WRITEBACK);
+	if (IS_ERR(wreq)) {
+		error = PTR_ERR(wreq);
+		goto couldnt_start;
+	}
+
+	__set_bit(NETFS_RREQ_OFFLOAD_COLLECTION, &wreq->flags);
+	trace_netfs_write(wreq, netfs_write_trace_writeback);
+	netfs_stat(&netfs_n_wh_writepages);
+
+	do {
+		_debug("wbiter %lx %llx", folio->index, atomic64_read(&wreq->issued_to));
+
+		/* It appears we don't have to handle cyclic writeback wrapping. */
+		WARN_ON_ONCE(wreq && folio_pos(folio) < atomic64_read(&wreq->issued_to));
+
+		if (netfs_folio_group(folio) != NETFS_FOLIO_COPY_TO_CACHE &&
+		    unlikely(!test_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags))) {
+			set_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags);
+			wreq->netfs_ops->begin_writeback(wreq);
+		}
+
+		error = netfs_write_folio(wreq, wbc, folio);
+		if (error == -ENOMEM) {
+			folio_redirty_for_writepage(wbc, folio);
+			folio_unlock(folio);
+		}
+	} while ((folio = writeback_iter(mapping, wbc, folio, &error)));
+
+	netfs_end_issue_write(wreq);
+	netfs_wake_collector(wreq);
+
+	netfs_put_request(wreq, netfs_rreq_trace_put_return);
+	_leave(" = %d", error);
+	return error;
+
+couldnt_start:
+	if (error == -ENOMEM) {
+		folio_redirty_for_writepage(wbc, folio);
+		folio_unlock(folio);
+		folio = writeback_iter(mapping, wbc, folio, &error);
+		WARN_ON_ONCE(folio != NULL);
+	} else {
+		netfs_kill_dirty_pages(mapping, wbc, folio);
+	}
+out:
+	netfs_wb_end(ictx);
+	_leave(" = %d", error);
+	return error;
+}
+EXPORT_SYMBOL(netfs_writepages);
+
+/*
+ * Begin a write operation for writing through the pagecache.
+ */
+struct netfs_io_request *netfs_begin_writethrough(struct kiocb *iocb, size_t len)
+{
+	struct netfs_io_request *wreq = NULL;
+	struct netfs_inode *ictx = netfs_inode(file_inode(iocb->ki_filp));
+
+	netfs_wb_begin(ictx, false);
+
+	wreq = netfs_create_write_req(iocb->ki_filp->f_mapping, iocb->ki_filp,
+				      iocb->ki_pos, NETFS_WRITETHROUGH);
+	if (IS_ERR(wreq)) {
+		netfs_wb_end(ictx);
+		return wreq;
+	}
+
+	wreq->io_streams[0].avail = true;
+	__set_bit(NETFS_RREQ_OFFLOAD_COLLECTION, &wreq->flags);
+	trace_netfs_write(wreq, netfs_write_trace_writethrough);
+	return wreq;
+}
+
+/*
+ * Advance the state of the write operation used when writing through the
+ * pagecache.  Data has been copied into the pagecache that we need to append
+ * to the request.  If we've added more than wsize then we need to create a new
+ * subrequest.
+ */
+int netfs_advance_writethrough(struct netfs_io_request *wreq, struct writeback_control *wbc,
+			       struct folio *folio, size_t copied, bool to_page_end,
+			       struct folio **writethrough_cache)
+{
+	int ret;
+
+	_enter("R=%x ic=%zu ws=%u cp=%zu tp=%u",
+	       wreq->debug_id, wreq->buffer.iter.count, wreq->wsize, copied, to_page_end);
+
+	/* The folio is locked. */
+
+	if (*writethrough_cache != folio) {
+		if (*writethrough_cache) {
+			/* Did the folio get moved? */
+			folio_put(*writethrough_cache);
+			*writethrough_cache = NULL;
+		}
+		/* We can make multiple writes to the folio... */
+		if (wreq->len == 0)
+			trace_netfs_folio(folio, netfs_folio_trace_wthru);
+		else
+			trace_netfs_folio(folio, netfs_folio_trace_wthru_plus);
+		*writethrough_cache = folio;
+		folio_get(folio);
+	}
+
+	wreq->len += copied;
+
+	if (!to_page_end) {
+		folio_mark_dirty(folio);
+		folio_unlock(folio);
+		return 0;
+	}
+
+	ret = netfs_write_folio(wreq, wbc, folio);
+	folio_put(*writethrough_cache);
+	*writethrough_cache = NULL;
+	wreq->submitted = wreq->len;
+	return ret;
+}
+
+/*
+ * End a write operation used when writing through the pagecache.
+ */
+ssize_t netfs_end_writethrough(struct netfs_io_request *wreq, struct writeback_control *wbc,
+			       struct folio *writethrough_cache)
+{
+	ssize_t ret;
+
+	_enter("R=%x", wreq->debug_id);
+
+	if (writethrough_cache) {
+		folio_lock(writethrough_cache);
+		netfs_write_folio(wreq, wbc, writethrough_cache);
+		folio_put(writethrough_cache);
+		wreq->submitted = wreq->len;
+	}
+
+	netfs_end_issue_write(wreq);
+
+	if (wreq->iocb)
+		ret = -EIOCBQUEUED;
+	else
+		ret = netfs_wait_for_write(wreq);
+	netfs_put_request(wreq, netfs_rreq_trace_put_return);
+	return ret;
+}
+
+/*
+ * Write some of a pending folio data back to the server and/or the cache.
+ */
+static int netfs_write_folio_single(struct netfs_io_request *wreq,
+				    struct folio *folio)
+{
+	struct netfs_io_stream *upload = &wreq->io_streams[0];
+	struct netfs_io_stream *cache  = &wreq->io_streams[1];
+	struct netfs_io_stream *stream;
+	size_t iter_off = 0;
+	size_t fsize = folio_size(folio), flen;
+	loff_t fpos = folio_pos(folio);
+	ssize_t ret;
+	bool to_eof = false;
+	bool no_debug = false;
+
+	_enter("");
+
+	flen = folio_size(folio);
+	if (flen > wreq->i_size - fpos) {
+		flen = wreq->i_size - fpos;
+		folio_zero_segment(folio, flen, fsize);
+		to_eof = true;
+	} else if (flen == wreq->i_size - fpos) {
+		to_eof = true;
+	}
+
+	_debug("folio %zx/%zx", flen, fsize);
+
+	if (!upload->avail && !cache->avail) {
+		trace_netfs_folio(folio, netfs_folio_trace_cancel_store);
+		return 0;
+	}
+
+	if (!upload->construct)
+		trace_netfs_folio(folio, netfs_folio_trace_store);
+	else
+		trace_netfs_folio(folio, netfs_folio_trace_store_plus);
+
+	/* Attach the folio to the rolling buffer. */
+	folio_get(folio);
+	ret = rolling_buffer_append(&wreq->buffer, folio, NETFS_ROLLBUF_PUT_MARK, wreq->gfp);
+	if (ret < 0) {
+		folio_put(folio);
+		return ret;
+	}
+
+	/* Move the submission point forward to allow for write-streaming data
+	 * not starting at the front of the page.  We don't do write-streaming
+	 * with the cache as the cache requires DIO alignment.
+	 *
+	 * Also skip uploading for data that's been read and just needs copying
+	 * to the cache.
+	 */
+	for (int s = 0; s < NR_IO_STREAMS; s++) {
+		stream = &wreq->io_streams[s];
+		stream->submit_off = 0;
+		stream->submit_len = flen;
+		if (!stream->avail) {
+			stream->submit_off = UINT_MAX;
+			stream->submit_len = 0;
+		}
+	}
+
+	/* Attach the folio to one or more subrequests.  For a big folio, we
+	 * could end up with thousands of subrequests if the wsize is small -
+	 * but we might need to wait during the creation of subrequests for
+	 * network resources (eg. SMB credits).
+	 */
+	for (;;) {
+		ssize_t part;
+		size_t lowest_off = ULONG_MAX;
+		int choose_s = -1;
+
+		/* Always add to the lowest-submitted stream first. */
+		for (int s = 0; s < NR_IO_STREAMS; s++) {
+			stream = &wreq->io_streams[s];
+			if (stream->submit_len > 0 &&
+			    stream->submit_off < lowest_off) {
+				lowest_off = stream->submit_off;
+				choose_s = s;
+			}
+		}
+
+		if (choose_s < 0)
+			break;
+		stream = &wreq->io_streams[choose_s];
+
+		/* Advance the iterator(s). */
+		if (stream->submit_off > iter_off) {
+			rolling_buffer_advance(&wreq->buffer, stream->submit_off - iter_off);
+			iter_off = stream->submit_off;
+		}
+
+		atomic64_set(&wreq->issued_to, fpos + stream->submit_off);
+		stream->submit_extendable_to = fsize - stream->submit_off;
+		part = netfs_advance_write(wreq, stream, fpos + stream->submit_off,
+					   stream->submit_len, to_eof);
+		stream->submit_off += part;
+		if (part > stream->submit_len)
+			stream->submit_len = 0;
+		else
+			stream->submit_len -= part;
+		if (part > 0)
+			no_debug = true;
+	}
+
+	wreq->buffer.iter.iov_offset = 0;
+	if (fsize > iter_off)
+		rolling_buffer_advance(&wreq->buffer, fsize - iter_off);
+	atomic64_set(&wreq->issued_to, fpos + fsize);
+
+	if (!no_debug)
+		kdebug("R=%x: No submit", wreq->debug_id);
+	_leave(" = 0");
+	return 0;
+}
+
+/**
+ * netfs_writeback_single - Write back a monolithic payload
+ * @mapping: The mapping to write from
+ * @wbc: Hints from the VM
+ * @iter: Data to write, must be ITER_FOLIOQ.
+ *
+ * Write a monolithic, non-pagecache object back to the server and/or
+ * the cache.
+ *
+ * Return: 0 if successful; 1 if skipped due to lock conflict and WB_SYNC_NONE;
+ * or a negative error code.
+ */
+int netfs_writeback_single(struct address_space *mapping,
+			   struct writeback_control *wbc,
+			   struct iov_iter *iter)
+{
+	struct netfs_io_request *wreq;
+	struct netfs_inode *ictx = netfs_inode(mapping->host);
+	struct folio_queue *fq;
+	size_t size = iov_iter_count(iter);
+	int ret;
+
+	if (WARN_ON_ONCE(!iov_iter_is_folioq(iter)))
+		return -EIO;
+
+	if (!netfs_wb_begin(ictx, wbc->sync_mode == WB_SYNC_NONE)) {
+		/* The VFS will have undirtied the inode. */
+		netfs_single_mark_inode_dirty(&ictx->inode);
+		return 1;
+	}
+
+	wreq = netfs_create_write_req(mapping, NULL, 0, NETFS_WRITEBACK_SINGLE);
+	if (IS_ERR(wreq)) {
+		ret = PTR_ERR(wreq);
+		goto couldnt_start;
+	}
+
+	__set_bit(NETFS_RREQ_OFFLOAD_COLLECTION, &wreq->flags);
+	trace_netfs_write(wreq, netfs_write_trace_writeback_single);
+	netfs_stat(&netfs_n_wh_writepages);
+
+	if (__test_and_set_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags))
+		wreq->netfs_ops->begin_writeback(wreq);
+
+	for (fq = (struct folio_queue *)iter->folioq; fq; fq = fq->next) {
+		for (int slot = 0; slot < folioq_count(fq); slot++) {
+			struct folio *folio = folioq_folio(fq, slot);
+			size_t part = umin(folioq_folio_size(fq, slot), size);
+
+			_debug("wbiter %lx %llx", folio->index, atomic64_read(&wreq->issued_to));
+
+			ret = netfs_write_folio_single(wreq, folio);
+			if (ret < 0)
+				goto stop;
+			size -= part;
+			if (size <= 0)
+				goto stop;
+		}
+	}
+
+stop:
+	for (int s = 0; s < NR_IO_STREAMS; s++)
+		netfs_issue_write(wreq, &wreq->io_streams[s]);
+	smp_wmb(); /* Write lists before ALL_QUEUED. */
+	set_bit(NETFS_RREQ_ALL_QUEUED, &wreq->flags);
+
+	netfs_wake_collector(wreq);
+
+	netfs_put_request(wreq, netfs_rreq_trace_put_return);
+	_leave(" = %d", ret);
+	return ret;
+
+couldnt_start:
+	netfs_wb_end(ictx);
+	_leave(" = %d", ret);
+	return ret;
+}
+EXPORT_SYMBOL(netfs_writeback_single);