[PATCH] mm: Removing the card during write

[laishangzhen <laishangzhen@163.com>]

operations blocks the I/O process
when during the process
Issue encountered:
When formatting an SD card to ext4 using mkfs.ext4,
if the card is ejected during the process,
the formatting process blocks at
balance_dirty_pages_ratelimited.

task:mkfs.ext4       state:D stack:
 0 pid:  900 ppid:   889 flags:0x00000000
 (__schedule)
 (schedule) from
 (schedule_timeout)
 (io_schedule_timeout)
 (balance_dirty_pages_ratelimited)
 (generic_perform_write)
 (__generic_file_write_iter)
 (blkdev_write_iter)
 (vfs_write)
 (ksys_pwrite64)
 Exception stack(0xc2283fa8 to 0xc2283ff0)

Modification approach:
After card ejection,
the dev in the bdi (backing_dev_info) is
released in del_gendisk.
Within generic_perform_write,
if writeback is supported,
it directly checks whether bdi->dev is NULL to determine
if the card has been ejected.
Once ejected, it becomes unnecessary to proceed
with page allocation and data writing.

Signed-off-by: laishangzhen <laishangzhen@163.com>
---
 mm/filemap.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index 6af6d8f29..5d6ba9f02 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -4087,6 +4087,8 @@ ssize_t generic_perform_write(struct kiocb *iocb, struct iov_iter *i)
 	struct address_space *mapping = file->f_mapping;
 	const struct address_space_operations *a_ops = mapping->a_ops;
 	size_t chunk = mapping_max_folio_size(mapping);
+	struct inode *inode = mapping->host;
+	struct backing_dev_info *bdi = inode_to_bdi(inode);
 	long status = 0;
 	ssize_t written = 0;
 
@@ -4101,6 +4103,12 @@ ssize_t generic_perform_write(struct kiocb *iocb, struct iov_iter *i)
 retry:
 		offset = pos & (chunk - 1);
 		bytes = min(chunk - offset, bytes);
+		if (bdi->capabilities & BDI_CAP_WRITEBACK) {
+			if (bdi->dev == NULL) {
+				status = -ENODEV;
+				break;
+			}
+		}
 		balance_dirty_pages_ratelimited(mapping);
 
 		if (fatal_signal_pending(current)) {
-- 
2.25.1