[PATCH 1/2] iomap: resched ioend completion when in non-atomic context

[Brian Foster <bfoster@redhat.com>]

The iomap ioend mechanism has the ability to construct very large,
contiguous bios and/or bio chains. This has been reported to lead to
soft lockup warnings in bio completion due to the amount of page
processing that occurs. Update the ioend completion path with a
parameter to indicate atomic context and insert a cond_resched()
call to avoid soft lockups in either scenario.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/iomap/buffered-io.c | 15 +++++++++------
 fs/xfs/xfs_aops.c      |  2 +-
 include/linux/iomap.h  |  2 +-
 3 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index bcfc288dba3f..5dfdb77a05b2 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1092,7 +1092,7 @@ iomap_finish_page_writeback(struct inode *inode, struct page *page,
  * ioend after this.
  */
 static void
-iomap_finish_ioend(struct iomap_ioend *ioend, int error)
+iomap_finish_ioend(struct iomap_ioend *ioend, int error, bool atomic)
 {
 	struct inode *inode = ioend->io_inode;
 	struct bio *bio = &ioend->io_inline_bio;
@@ -1115,8 +1115,11 @@ iomap_finish_ioend(struct iomap_ioend *ioend, int error)
 			next = bio->bi_private;
 
 		/* walk each page on bio, ending page IO on them */
-		bio_for_each_segment_all(bv, bio, iter_all)
+		bio_for_each_segment_all(bv, bio, iter_all) {
 			iomap_finish_page_writeback(inode, bv->bv_page, error);
+			if (!atomic)
+				cond_resched();
+		}
 		bio_put(bio);
 	}
 	/* The ioend has been freed by bio_put() */
@@ -1129,17 +1132,17 @@ iomap_finish_ioend(struct iomap_ioend *ioend, int error)
 }
 
 void
-iomap_finish_ioends(struct iomap_ioend *ioend, int error)
+iomap_finish_ioends(struct iomap_ioend *ioend, int error, bool atomic)
 {
 	struct list_head tmp;
 
 	list_replace_init(&ioend->io_list, &tmp);
-	iomap_finish_ioend(ioend, error);
+	iomap_finish_ioend(ioend, error, atomic);
 
 	while (!list_empty(&tmp)) {
 		ioend = list_first_entry(&tmp, struct iomap_ioend, io_list);
 		list_del_init(&ioend->io_list);
-		iomap_finish_ioend(ioend, error);
+		iomap_finish_ioend(ioend, error, atomic);
 	}
 }
 EXPORT_SYMBOL_GPL(iomap_finish_ioends);
@@ -1208,7 +1211,7 @@ static void iomap_writepage_end_bio(struct bio *bio)
 {
 	struct iomap_ioend *ioend = bio->bi_private;
 
-	iomap_finish_ioend(ioend, blk_status_to_errno(bio->bi_status));
+	iomap_finish_ioend(ioend, blk_status_to_errno(bio->bi_status), true);
 }
 
 /*
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index b35611882ff9..3e061ea99922 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -188,7 +188,7 @@ xfs_end_ioend(
 done:
 	if (ioend->io_private)
 		error = xfs_setfilesize_ioend(ioend, error);
-	iomap_finish_ioends(ioend, error);
+	iomap_finish_ioends(ioend, error, false);
 	memalloc_nofs_restore(nofs_flag);
 }
 
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 4d1d3c3469e9..4d3778dc4318 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -229,7 +229,7 @@ struct iomap_writepage_ctx {
 	const struct iomap_writeback_ops *ops;
 };
 
-void iomap_finish_ioends(struct iomap_ioend *ioend, int error);
+void iomap_finish_ioends(struct iomap_ioend *ioend, int error, bool atomic);
 void iomap_ioend_try_merge(struct iomap_ioend *ioend,
 		struct list_head *more_ioends,
 		void (*merge_private)(struct iomap_ioend *ioend,
-- 
2.25.4