[PATCH 1/4] f2fs: compress: fix deadloop in f2fs_write_cache_pages()

[Chao Yu]

With below mount option and testcase, it hangs kernel.

1. mount -t f2fs -o compress_log_size=5 /dev/vdb /mnt/f2fs
2. touch /mnt/f2fs/file
3. chattr +c /mnt/f2fs/file
4. dd if=/dev/zero of=/mnt/f2fs/file bs=1MB count=1
5. sync
6. dd if=/dev/zero of=/mnt/f2fs/file bs=111 count=11 conv=notrunc
7. sync

INFO: task sync:4788 blocked for more than 120 seconds.
      Not tainted 6.5.0-rc1+ #322
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:sync            state:D stack:0     pid:4788  ppid:509    flags:0x00000002
Call Trace:
 <TASK>
 __schedule+0x335/0xf80
 schedule+0x6f/0xf0
 wb_wait_for_completion+0x5e/0x90
 sync_inodes_sb+0xd8/0x2a0
 sync_inodes_one_sb+0x1d/0x30
 iterate_supers+0x99/0xf0
 ksys_sync+0x46/0xb0
 __do_sys_sync+0x12/0x20
 do_syscall_64+0x3f/0x90
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

The reason is f2fs_all_cluster_page_ready() assumes that pages array should
cover at least one cluster, otherwise, it will always return false, result
in deadloop.

By default, pages array size is 16, and it can cover the case cluster_size
is equal or less than 16, for the case cluster_size is larger than 16, let's
allocate memory of pages array dynamically.

Fixes: 4c8ff7095bef ("f2fs: support data compression")
Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
---
 fs/f2fs/data.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 916e317ac925..3f33e14dc7f8 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -3023,7 +3023,8 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 {
 	int ret = 0;
 	int done = 0, retry = 0;
-	struct page *pages[F2FS_ONSTACK_PAGES];
+	struct page *pages_local[F2FS_ONSTACK_PAGES];
+	struct page **pages = pages_local;
 	struct folio_batch fbatch;
 	struct f2fs_sb_info *sbi = F2FS_M_SB(mapping);
 	struct bio *bio = NULL;
@@ -3047,6 +3048,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 #endif
 	int nr_folios, p, idx;
 	int nr_pages;
+	unsigned int max_pages = F2FS_ONSTACK_PAGES;
 	pgoff_t index;
 	pgoff_t end;		/* Inclusive */
 	pgoff_t done_index;
@@ -3056,6 +3058,15 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 	int submitted = 0;
 	int i;
 
+#ifdef CONFIG_F2FS_FS_COMPRESSION
+	if (f2fs_compressed_file(inode) &&
+		1 << cc.log_cluster_size > F2FS_ONSTACK_PAGES) {
+		pages = f2fs_kzalloc(sbi, sizeof(struct page *) <<
+				cc.log_cluster_size, GFP_NOFS | __GFP_NOFAIL);
+		max_pages = 1 << cc.log_cluster_size;
+	}
+#endif
+
 	folio_batch_init(&fbatch);
 
 	if (get_dirty_pages(mapping->host) <=
@@ -3101,7 +3112,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 add_more:
 			pages[nr_pages] = folio_page(folio, idx);
 			folio_get(folio);
-			if (++nr_pages == F2FS_ONSTACK_PAGES) {
+			if (++nr_pages == max_pages) {
 				index = folio->index + idx + 1;
 				folio_batch_release(&fbatch);
 				goto write;
@@ -3283,6 +3294,11 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 	if (bio)
 		f2fs_submit_merged_ipu_write(sbi, &bio, NULL);
 
+#ifdef CONFIG_F2FS_FS_COMPRESSION
+	if (pages != pages_local)
+		kfree(pages);
+#endif
+
 	return ret;
 }
 
-- 
2.40.1