[PATCH v6 12/24] netfs: Remove the writethrough code

[David Howells <dhowells@redhat.com>]

Remove the netfs writethrough code as it's very tricky to get the locking
right and it will probably deadlock if used in conjunction with Ceph snapshots
because it excludes writeback for the duration, but to flush out old
snapshots, it does a synchronous flush that invokes writeback.

Instead, O_SYNC writes do a flush after performing the write - which is
already there as the callers of netfs_perform_write() all call
generic_write_sync().

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Paulo Alcantara <pc@manguebit.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/9p/vfs_addr.c             |   1 -
 fs/afs/file.c                |   1 -
 fs/netfs/buffered_write.c    |  56 ++-----------------
 fs/netfs/internal.h          |   7 ---
 fs/netfs/main.c              |   1 -
 fs/netfs/write_collect.c     |   2 -
 fs/netfs/write_issue.c       | 104 +----------------------------------
 include/linux/netfs.h        |   1 -
 include/trace/events/netfs.h |   8 +--
 9 files changed, 8 insertions(+), 173 deletions(-)

diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index 1ac0b3dcc077..2129fcb0f65c 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -124,7 +124,6 @@ static int v9fs_init_request(struct netfs_io_request *rreq, struct file *file)
 	struct p9_fid *fid;
 	struct dentry *dentry;
 	bool writing = (rreq->origin == NETFS_READ_FOR_WRITE ||
-			rreq->origin == NETFS_WRITETHROUGH ||
 			rreq->origin == NETFS_UNBUFFERED_WRITE ||
 			rreq->origin == NETFS_DIO_WRITE);
 
diff --git a/fs/afs/file.c b/fs/afs/file.c
index 0467742bfeee..3617c245f319 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -400,7 +400,6 @@ static int afs_init_request(struct netfs_io_request *rreq, struct file *file)
 		}
 		break;
 	case NETFS_WRITEBACK:
-	case NETFS_WRITETHROUGH:
 	case NETFS_UNBUFFERED_WRITE:
 	case NETFS_DIO_WRITE:
 		if (S_ISREG(rreq->inode->i_mode))
diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index 2cdb68e6b16f..39f00b326e0f 100644
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -91,44 +91,14 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 	struct inode *inode = file_inode(file);
 	struct address_space *mapping = inode->i_mapping;
 	struct netfs_inode *ctx = netfs_inode(inode);
-	struct writeback_control wbc = {
-		.sync_mode	= WB_SYNC_NONE,
-		.for_sync	= true,
-		.nr_to_write	= LONG_MAX,
-		.range_start	= iocb->ki_pos,
-		.range_end	= iocb->ki_pos + iter->count,
-	};
-	struct netfs_io_request *wreq = NULL;
-	struct folio *folio = NULL, *writethrough = NULL;
+	struct folio *folio = NULL;
 	unsigned int bdp_flags = (iocb->ki_flags & IOCB_NOWAIT) ? BDP_ASYNC : 0;
-	ssize_t written = 0, ret, ret2;
+	ssize_t written = 0, ret;
 	loff_t pos = iocb->ki_pos;
 	size_t max_chunk = mapping_max_folio_size(mapping);
 	bool maybe_trouble = false;
 
-	if (unlikely(iocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC))
-	    ) {
-		wbc_attach_fdatawrite_inode(&wbc, mapping->host);
-
-		ret = filemap_write_and_wait_range(mapping, pos, pos + iter->count);
-		if (ret < 0) {
-			wbc_detach_inode(&wbc);
-			goto out;
-		}
-
-		wreq = netfs_begin_writethrough(iocb, iter->count);
-		if (IS_ERR(wreq)) {
-			wbc_detach_inode(&wbc);
-			ret = PTR_ERR(wreq);
-			wreq = NULL;
-			goto out;
-		}
-		if (!is_sync_kiocb(iocb))
-			wreq->iocb = iocb;
-		netfs_stat(&netfs_n_wh_writethrough);
-	} else {
-		netfs_stat(&netfs_n_wh_buffered_write);
-	}
+	netfs_stat(&netfs_n_wh_buffered_write);
 
 	do {
 		enum netfs_folio_trace trace;
@@ -390,15 +360,8 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 		pos += copied;
 		written += copied;
 
-		if (likely(!wreq)) {
-			folio_mark_dirty(folio);
-			folio_unlock(folio);
-		} else {
-			netfs_advance_writethrough(wreq, &wbc, folio, copied,
-						   offset + copied == flen,
-						   &writethrough);
-			/* Folio unlocked */
-		}
+		folio_mark_dirty(folio);
+		folio_unlock(folio);
 	retry:
 		folio_put(folio);
 		folio = NULL;
@@ -420,15 +383,6 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 			ctx->ops->post_modify(inode);
 	}
 
-	if (unlikely(wreq)) {
-		ret2 = netfs_end_writethrough(wreq, &wbc, writethrough);
-		wbc_detach_inode(&wbc);
-		if (ret2 == -EIOCBQUEUED)
-			return ret2;
-		if (ret == 0 && ret2 < 0)
-			ret = ret2;
-	}
-
 	iocb->ki_pos += written;
 	_leave(" = %zd [%zd]", written, ret);
 	return written ? written : ret;
diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 8cb74cb8242a..5160f14f861c 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -154,7 +154,6 @@ extern atomic_t netfs_n_rh_write_zskip;
 extern atomic_t netfs_n_rh_retry_read_req;
 extern atomic_t netfs_n_rh_retry_read_subreq;
 extern atomic_t netfs_n_wh_buffered_write;
-extern atomic_t netfs_n_wh_writethrough;
 extern atomic_t netfs_n_wh_dio_write;
 extern atomic_t netfs_n_wh_writepages;
 extern atomic_t netfs_n_wh_copy_to_cache;
@@ -214,12 +213,6 @@ void netfs_issue_write(struct netfs_io_request *wreq,
 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_request *netfs_begin_writethrough(struct kiocb *iocb, size_t len);
-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);
-ssize_t netfs_end_writethrough(struct netfs_io_request *wreq, struct writeback_control *wbc,
-			       struct folio *writethrough_cache);
 
 /*
  * write_retry.c
diff --git a/fs/netfs/main.c b/fs/netfs/main.c
index 73da6c9f5777..6a5a6b1b10a3 100644
--- a/fs/netfs/main.c
+++ b/fs/netfs/main.c
@@ -43,7 +43,6 @@ static const char *netfs_origins[nr__netfs_io_origin] = {
 	[NETFS_DIO_READ]		= "DR",
 	[NETFS_WRITEBACK]		= "WB",
 	[NETFS_WRITEBACK_SINGLE]	= "W1",
-	[NETFS_WRITETHROUGH]		= "WT",
 	[NETFS_UNBUFFERED_WRITE]	= "UW",
 	[NETFS_DIO_WRITE]		= "DW",
 	[NETFS_PGPRIV2_COPY_TO_CACHE]	= "2C",
diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index 210eb8f3958d..2eac588e37de 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -214,7 +214,6 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 	smp_rmb();
 	collected_to = ULLONG_MAX;
 	if (wreq->origin == NETFS_WRITEBACK ||
-	    wreq->origin == NETFS_WRITETHROUGH ||
 	    wreq->origin == NETFS_PGPRIV2_COPY_TO_CACHE)
 		notes = NEED_UNLOCK;
 	else
@@ -411,7 +410,6 @@ bool netfs_write_collection(struct netfs_io_request *wreq)
 	switch (wreq->origin) {
 	case NETFS_WRITEBACK:
 	case NETFS_WRITEBACK_SINGLE:
-	case NETFS_WRITETHROUGH:
 		netfs_wb_end(ictx);
 		break;
 	default:
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 33cc7a8c8394..7cb679b0de8f 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -96,7 +96,6 @@ struct netfs_io_request *netfs_create_write_req(struct address_space *mapping,
 	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);
@@ -365,11 +364,7 @@ static int netfs_write_folio(struct netfs_io_request *wreq,
 		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) {
+	if (flen > i_size - fpos) {
 		flen = i_size - fpos;
 		if (!streamw)
 			folio_zero_segment(folio, flen, fsize);
@@ -611,103 +606,6 @@ int netfs_writepages(struct address_space *mapping,
 }
 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;
-}
-
 /**
  * netfs_writeback_single - Write back a monolithic payload
  * @mapping: The mapping to write from
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 787670c2e134..c724a68c2e20 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -210,7 +210,6 @@ enum netfs_io_origin {
 	NETFS_DIO_READ,			/* This is a direct I/O read */
 	NETFS_WRITEBACK,		/* This write was triggered by writepages */
 	NETFS_WRITEBACK_SINGLE,		/* This monolithic write was triggered by writepages */
-	NETFS_WRITETHROUGH,		/* This write was made by netfs_perform_write() */
 	NETFS_UNBUFFERED_WRITE,		/* This is an unbuffered write */
 	NETFS_DIO_WRITE,		/* This is a direct I/O write */
 	NETFS_PGPRIV2_COPY_TO_CACHE,	/* [DEPRECATED] This is writing read data to the cache */
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index 5354a0439324..2ce162baaad1 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -30,8 +30,7 @@
 	EM(netfs_write_trace_dio_write,		"DIO-WRITE")	\
 	EM(netfs_write_trace_unbuffered_write,	"UNB-WRITE")	\
 	EM(netfs_write_trace_writeback,		"WRITEBACK")	\
-	EM(netfs_write_trace_writeback_single,	"WB-SINGLE") \
-	E_(netfs_write_trace_writethrough,	"WRITETHRU")
+	E_(netfs_write_trace_writeback_single,	"WB-SINGLE")
 
 #define netfs_rreq_origins					\
 	EM(NETFS_READAHEAD,			"RA")		\
@@ -43,7 +42,6 @@
 	EM(NETFS_DIO_READ,			"DR")		\
 	EM(NETFS_WRITEBACK,			"WB")		\
 	EM(NETFS_WRITEBACK_SINGLE,		"W1")		\
-	EM(NETFS_WRITETHROUGH,			"WT")		\
 	EM(NETFS_UNBUFFERED_WRITE,		"UW")		\
 	EM(NETFS_DIO_WRITE,			"DW")		\
 	E_(NETFS_PGPRIV2_COPY_TO_CACHE,		"2C")
@@ -221,9 +219,7 @@
 	EM(netfs_folio_trace_redirtied,		"redirtied")	\
 	EM(netfs_folio_trace_store,		"store")	\
 	EM(netfs_folio_trace_store_copy,	"store-copy")	\
-	EM(netfs_folio_trace_store_plus,	"store+")	\
-	EM(netfs_folio_trace_wthru,		"wthru")	\
-	E_(netfs_folio_trace_wthru_plus,	"wthru+")
+	E_(netfs_folio_trace_store_plus,	"store+")
 
 #define netfs_collect_contig_traces				\
 	EM(netfs_contig_trace_collect,		"Collect")	\