[PATCH 1/5] mm/filemap: gate dropbehind invalidate on folio !dirty && !writeback

[PATCH 1/5] mm/filemap: gate dropbehind invalidate on folio !dirty && !writeback

[Jens Axboe]

It's possible for the folio to either get marked for writeback or
redirtied. Add a helper, filemap_end_dropbehind(), which guards the
folio_unmap_invalidate() call behind check for the folio being both
non-dirty and not under writeback AFTER the folio lock has been
acquired. Use this helper folio_end_dropbehind_write().

Cc: stable@vger.kernel.org
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: fb7d3bc41493 ("mm/filemap: drop streaming/uncached pages when writeback completes")
Link: https://lore.kernel.org/linux-fsdevel/20250525083209.GS2023217@ZenIV/
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 mm/filemap.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 7b90cbeb4a1a..008a55290f34 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1589,6 +1589,16 @@ int folio_wait_private_2_killable(struct folio *folio)
 }
 EXPORT_SYMBOL(folio_wait_private_2_killable);
 
+static void filemap_end_dropbehind(struct folio *folio)
+{
+	struct address_space *mapping = folio->mapping;
+
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+
+	if (mapping && !folio_test_writeback(folio) && !folio_test_dirty(folio))
+		folio_unmap_invalidate(mapping, folio, 0);
+}
+
 /*
  * If folio was marked as dropbehind, then pages should be dropped when writeback
  * completes. Do that now. If we fail, it's likely because of a big folio -
@@ -1604,8 +1614,7 @@ static void folio_end_dropbehind_write(struct folio *folio)
 	 * invalidation in that case.
 	 */
 	if (in_task() && folio_trylock(folio)) {
-		if (folio->mapping)
-			folio_unmap_invalidate(folio->mapping, folio, 0);
+		filemap_end_dropbehind(folio);
 		folio_unlock(folio);
 	}
 }
-- 
2.49.0

[PATCH 2/5] mm/filemap: use filemap_end_dropbehind() for read invalidation

[Jens Axboe]

Use the filemap_end_dropbehind() helper rather than calling
folio_unmap_invalidate() directly, as we need to check if the folio has
been redirtied or marked for writeback once the folio lock has been
re-acquired.

Cc: stable@vger.kernel.org
Reported-by: Trond Myklebust <trondmy@hammerspace.com>
Fixes: 8026e49bff9b ("mm/filemap: add read support for RWF_DONTCACHE")
Link: https://lore.kernel.org/linux-fsdevel/ba8a9805331ce258a622feaca266b163db681a10.camel@hammerspace.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 mm/filemap.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 008a55290f34..6af6d8f2929c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2644,8 +2644,7 @@ static inline bool pos_same_folio(loff_t pos1, loff_t pos2, struct folio *folio)
 	return (pos1 >> shift == pos2 >> shift);
 }
 
-static void filemap_end_dropbehind_read(struct address_space *mapping,
-					struct folio *folio)
+static void filemap_end_dropbehind_read(struct folio *folio)
 {
 	if (!folio_test_dropbehind(folio))
 		return;
@@ -2653,7 +2652,7 @@ static void filemap_end_dropbehind_read(struct address_space *mapping,
 		return;
 	if (folio_trylock(folio)) {
 		if (folio_test_clear_dropbehind(folio))
-			folio_unmap_invalidate(mapping, folio, 0);
+			filemap_end_dropbehind(folio);
 		folio_unlock(folio);
 	}
 }
@@ -2774,7 +2773,7 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
 		for (i = 0; i < folio_batch_count(&fbatch); i++) {
 			struct folio *folio = fbatch.folios[i];
 
-			filemap_end_dropbehind_read(mapping, folio);
+			filemap_end_dropbehind_read(folio);
 			folio_put(folio);
 		}
 		folio_batch_init(&fbatch);
-- 
2.49.0

Re: [PATCH 1/5] mm/filemap: gate dropbehind invalidate on folio !dirty && !writeback

[Christoph Hellwig]

On Tue, May 27, 2025 at 07:28:52AM -0600, Jens Axboe wrote:
> It's possible for the folio to either get marked for writeback or
> redirtied. Add a helper, filemap_end_dropbehind(), which guards the
> folio_unmap_invalidate() call behind check for the folio being both
> non-dirty and not under writeback AFTER the folio lock has been
> acquired. Use this helper folio_end_dropbehind_write().

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 2/5] mm/filemap: use filemap_end_dropbehind() for read invalidation

[Christoph Hellwig]

On Tue, May 27, 2025 at 07:28:53AM -0600, Jens Axboe wrote:
> Use the filemap_end_dropbehind() helper rather than calling
> folio_unmap_invalidate() directly, as we need to check if the folio has
> been redirtied or marked for writeback once the folio lock has been
> re-acquired.

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>