Unverified Commit cce6bfa6 authored by David Howells's avatar David Howells Committed by Christian Brauner
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netfs: Fix trimming of streaming-write folios in netfs_inval_folio() 



When netfslib writes to a folio that it doesn't have data for, but that
data exists on the server, it will make a 'streaming write' whereby it
stores data in a folio that is marked dirty, but not uptodate.  When it
does this, it attaches a record to folio->private to track the dirty
region.

When truncate() or fallocate() wants to invalidate part of such a folio, it
will call into ->invalidate_folio(), specifying the part of the folio that
is to be invalidated.  netfs_invalidate_folio(), on behalf of the
filesystem, must then determine how to trim the streaming write record.  In
a couple of cases, however, it does this incorrectly (the reduce-length and
move-start cases are switched over and don't, in any case, calculate the
value correctly).

Fix this by making the logic tree more obvious and fixing the cases.

Fixes: 9ebff83e ("netfs: Prep to use folio->private for write grouping and streaming write")
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20240823200819.532106-5-dhowells@redhat.com


cc: Matthew Wilcox (Oracle) <willy@infradead.org>
cc: Pankaj Raghav <p.raghav@samsung.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: netfs@lists.linux.dev
cc: linux-mm@kvack.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 7dfc8f0c

fs/netfs/misc.c

+35 −15
Original line number Diff line number Diff line
@@ -97,10 +97,20 @@ EXPORT_SYMBOL(netfs_clear_inode_writeback); 
void netfs_invalidate_folio(struct folio *folio, size_t offset, size_t length)

{

	struct netfs_folio *finfo;

	struct netfs_inode *ctx = netfs_inode(folio_inode(folio));

	size_t flen = folio_size(folio);



	_enter("{%lx},%zx,%zx", folio->index, offset, length);



	if (offset == 0 && length == flen) {

		unsigned long long i_size = i_size_read(&ctx->inode);

		unsigned long long fpos = folio_pos(folio), end;



		end = umin(fpos + flen, i_size);

		if (fpos < i_size && end > ctx->zero_point)

			ctx->zero_point = end;

	}



	folio_wait_private_2(folio); /* [DEPRECATED] */



	if (!folio_test_private(folio))
@@ -115,18 +125,34 @@ void netfs_invalidate_folio(struct folio *folio, size_t offset, size_t length) 
		/* We have a partially uptodate page from a streaming write. */

		unsigned int fstart = finfo->dirty_offset;

		unsigned int fend = fstart + finfo->dirty_len;

		unsigned int end = offset + length;

		unsigned int iend = offset + length;



		if (offset >= fend)

			return;

		if (end <= fstart)

		if (iend <= fstart)

			return;

		if (offset <= fstart && end >= fend)



		/* The invalidation region overlaps the data.  If the region

		 * covers the start of the data, we either move along the start

		 * or just erase the data entirely.

		 */

		if (offset <= fstart) {

			if (iend >= fend)

				goto erase_completely;

		if (offset <= fstart && end > fstart)

			goto reduce_len;

		if (offset > fstart && end >= fend)

			goto move_start;

			/* Move the start of the data. */

			finfo->dirty_len = fend - iend;

			finfo->dirty_offset = offset;

			return;

		}



		/* Reduce the length of the data if the invalidation region

		 * covers the tail part.

		 */

		if (iend >= fend) {

			finfo->dirty_len = offset - fstart;

			return;

		}



		/* A partial write was split.  The caller has already zeroed

		 * it, so just absorb the hole.

		 */
@@ -139,12 +165,6 @@ void netfs_invalidate_folio(struct folio *folio, size_t offset, size_t length) 
	folio_clear_uptodate(folio);

	kfree(finfo);

	return;

reduce_len:

	finfo->dirty_len = offset + length - finfo->dirty_offset;

	return;

move_start:

	finfo->dirty_len -= offset - finfo->dirty_offset;

	finfo->dirty_offset = offset;

}

EXPORT_SYMBOL(netfs_invalidate_folio);
@@ -164,7 +184,7 @@ bool netfs_release_folio(struct folio *folio, gfp_t gfp) 
	if (folio_test_dirty(folio))

		return false;



	end = folio_pos(folio) + folio_size(folio);

	end = umin(folio_pos(folio) + folio_size(folio), i_size_read(&ctx->inode));

	if (end > ctx->zero_point)

		ctx->zero_point = end;