[PATCH v6 2/4] iomap: use BIO_COMPLETE_IN_TASK for dropbehind writeback

[Tal Zussman <tz2294@columbia.edu>]

Set BIO_COMPLETE_IN_TASK on iomap writeback bios when a dropbehind folio
is added. This ensures that bi_end_io runs in task context, where
folio_end_dropbehind() can safely invalidate folios.

With the bio layer now handling task-context deferral generically,
IOMAP_IOEND_DONTCACHE is no longer needed, as XFS no longer needs to
route DONTCACHE ioends through its completion workqueue. Remove the flag
and its NOMERGE entry.

Without the NOMERGE, regular I/Os that get merged with a dropbehind
folio will also have their completion deferred to task context.

Signed-off-by: Tal Zussman <tz2294@columbia.edu>
---
 fs/iomap/ioend.c      | 5 +++--
 fs/xfs/xfs_aops.c     | 4 ----
 include/linux/iomap.h | 5 +----
 3 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/fs/iomap/ioend.c b/fs/iomap/ioend.c
index acf3cf98b23a..892dbfc77ae9 100644
--- a/fs/iomap/ioend.c
+++ b/fs/iomap/ioend.c
@@ -237,8 +237,6 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
 
 	if (wpc->iomap.flags & IOMAP_F_SHARED)
 		ioend_flags |= IOMAP_IOEND_SHARED;
-	if (folio_test_dropbehind(folio))
-		ioend_flags |= IOMAP_IOEND_DONTCACHE;
 	if (pos == wpc->iomap.offset && (wpc->iomap.flags & IOMAP_F_BOUNDARY))
 		ioend_flags |= IOMAP_IOEND_BOUNDARY;
 
@@ -255,6 +253,9 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
 	if (!bio_add_folio(&ioend->io_bio, folio, map_len, poff))
 		goto new_ioend;
 
+	if (folio_test_dropbehind(folio))
+		bio_set_flag(&ioend->io_bio, BIO_COMPLETE_IN_TASK);
+
 	/*
 	 * Clamp io_offset and io_size to the incore EOF so that ondisk
 	 * file size updates in the ioend completion are byte-accurate.
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index f279055fcea0..0dcf78beae8a 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -511,10 +511,6 @@ xfs_ioend_needs_wq_completion(
 	if (ioend->io_flags & (IOMAP_IOEND_UNWRITTEN | IOMAP_IOEND_SHARED))
 		return true;
 
-	/* Page cache invalidation cannot be done in irq context. */
-	if (ioend->io_flags & IOMAP_IOEND_DONTCACHE)
-		return true;
-
 	return false;
 }
 
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 2c5685adf3a9..fef04e01116f 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -399,16 +399,13 @@ sector_t iomap_bmap(struct address_space *mapping, sector_t bno,
 #define IOMAP_IOEND_BOUNDARY		(1U << 2)
 /* is direct I/O */
 #define IOMAP_IOEND_DIRECT		(1U << 3)
-/* is DONTCACHE I/O */
-#define IOMAP_IOEND_DONTCACHE		(1U << 4)
 
 /*
  * Flags that if set on either ioend prevent the merge of two ioends.
  * (IOMAP_IOEND_BOUNDARY also prevents merges, but only one-way)
  */
 #define IOMAP_IOEND_NOMERGE_FLAGS \
-	(IOMAP_IOEND_SHARED | IOMAP_IOEND_UNWRITTEN | IOMAP_IOEND_DIRECT | \
-	 IOMAP_IOEND_DONTCACHE)
+	(IOMAP_IOEND_SHARED | IOMAP_IOEND_UNWRITTEN | IOMAP_IOEND_DIRECT)
 
 /*
  * Structure for writeback I/O completions.

-- 
2.39.5