From bde708f1a65d025c45575bfe1e7bf7bdf7e71e87 Mon Sep 17 00:00:00 2001
From: Alistair Popple <apopple@nvidia.com>
Date: Fri, 28 Feb 2025 14:31:01 +1100
Subject: fs/dax: always remove DAX page-cache entries when breaking layouts

Prior to any truncation operations file systems call dax_break_mapping()
to ensure pages in the range are not under going DMA.  Later DAX
page-cache entries will be removed by truncate_folio_batch_exceptionals()
in the generic page-cache code.

However this makes it possible for folios to be removed from the
page-cache even though they are still DMA busy if the file-system hasn't
called dax_break_mapping().  It also means they can never be waited on in
future because FS DAX will lose track of them once the page-cache entry
has been deleted.

Instead it is better to delete the FS DAX entry when the file-system calls
dax_break_mapping() as part of it's truncate operation.  This ensures only
idle pages can be removed from the FS DAX page-cache and makes it easy to
detect if a file-system hasn't called dax_break_mapping() prior to a
truncate operation.

Link: https://lkml.kernel.org/r/3be6115eaaa8d28fee37fcba3287be4f226a7d24.1740713401.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Alison Schofield <alison.schofield@intel.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Asahi Lina <lina@asahilina.net>
Cc: Balbir Singh <balbirs@nvidia.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: linmiaohe <linmiaohe@huawei.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Michael "Camp Drill Sergeant" Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Ted Ts'o <tytso@mit.edu>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/truncate.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

(limited to 'mm/truncate.c')

diff --git a/mm/truncate.c b/mm/truncate.c
index 76d8fcd89bd0..79570045071c 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -78,8 +78,22 @@ static void truncate_folio_batch_exceptionals(struct address_space *mapping,
 
 	if (dax_mapping(mapping)) {
 		for (i = j; i < nr; i++) {
-			if (xa_is_value(fbatch->folios[i]))
+			if (xa_is_value(fbatch->folios[i])) {
+				/*
+				 * File systems should already have called
+				 * dax_break_layout_entry() to remove all DAX
+				 * entries while holding a lock to prevent
+				 * establishing new entries. Therefore we
+				 * shouldn't find any here.
+				 */
+				WARN_ON_ONCE(1);
+
+				/*
+				 * Delete the mapping so truncate_pagecache()
+				 * doesn't loop forever.
+				 */
 				dax_delete_mapping_entry(mapping, indices[i]);
+			}
 		}
 		goto out;
 	}
-- 
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