[PATCH] exfat: drain dirty pages after forced shutdown

[Chi Zhiling <chizhiling@163.com>]

From: Chi Zhiling <chizhiling@kylinos.cn>

A forced shutdown sets EXFAT_FLAGS_SHUTDOWN, after which
exfat_writepages() returns -EIO.  Pages dirtied before the shutdown can
then never be written back, so a writer throttled in
balance_dirty_pages() while extending valid_size sleeps forever.

Stuck stack:

  balance_dirty_pages+0x4f0/0xb40
  exfat_prepare_valid_range+0x43/0x140
  exfat_file_write_iter+0x413/0x520
  iter_file_splice_write+0x32d/0x5a0
  direct_splice_actor+0x51/0x270
  splice_direct_to_actor+0xf5/0x270
  do_splice_direct+0x76/0xc0
  vfs_copy_file_range+0x244/0x710
  __do_sys_copy_file_range+0xe6/0x240
  do_syscall_64+0x106/0x5f0
  entry_SYSCALL_64_after_hwframe+0x77/0x7f

Allow writeback of pages dirtied before the shutdown to drain.  New
writes are still rejected in exfat_write_iomap_begin() and
exfat_prepare_valid_range().

Fixes: f761fcdd289d0 ("exfat: Implement sops->shutdown and ioctl")
Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
---
 fs/exfat/file.c  | 3 +++
 fs/exfat/inode.c | 3 ---
 fs/exfat/iomap.c | 3 +++
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/exfat/file.c b/fs/exfat/file.c
index 1386149916bb..8b9fadba363f 100644
--- a/fs/exfat/file.c
+++ b/fs/exfat/file.c
@@ -735,6 +735,9 @@ static int exfat_prepare_valid_range(struct inode *inode, loff_t start,
 		index = pos >> PAGE_SHIFT;
 		next = min(((loff_t)index + 1) << PAGE_SHIFT, end);
 
+		if (exfat_forced_shutdown(inode->i_sb))
+			return -EIO;
+
 		balance_dirty_pages_ratelimited(mapping);
 
 		folio = read_mapping_folio(mapping, index, NULL);
diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
index 5129df1e79b4..4bea9e9deb94 100644
--- a/fs/exfat/inode.c
+++ b/fs/exfat/inode.c
@@ -283,9 +283,6 @@ static int exfat_writepages(struct address_space *mapping,
 		.ops		= &exfat_writeback_ops,
 	};
 
-	if (unlikely(exfat_forced_shutdown(mapping->host->i_sb)))
-		return -EIO;
-
 	return iomap_writepages(&wpc);
 }
 
diff --git a/fs/exfat/iomap.c b/fs/exfat/iomap.c
index e50ecbfbfbe0..6383739f5700 100644
--- a/fs/exfat/iomap.c
+++ b/fs/exfat/iomap.c
@@ -165,6 +165,9 @@ static int exfat_write_iomap_begin(struct inode *inode, loff_t offset, loff_t le
 	loff_t end;
 	int err;
 
+	if (exfat_forced_shutdown(inode->i_sb))
+		return -EIO;
+
 	err = __exfat_iomap_begin(inode, offset, length, flags, iomap, true);
 	if (err || flags & (IOMAP_DIRECT | IOMAP_FAULT) ||
 	    iomap->flags & IOMAP_F_NEW)
-- 
2.53.0