[f2fs-dev] [PATCH] f2fs: fix potential deadloop in prepare_compress_overwrite()

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

Jan Prusakowski reported a kernel hang issue as below:

When running xfstests on linux-next kernel (6.14.0-rc3, 6.12) I
encountered a problem in generic/475 test where fsstress process
gets blocked in __f2fs_write_data_pages() and the test hangs.
The options I used are:

MKFS_OPTIONS  -- -O compression -O extra_attr -O project_quota -O quota /dev/vdc
MOUNT_OPTIONS -- -o acl,user_xattr -o discard,compress_extension=* /dev/vdc /vdc

INFO: task kworker/u8:0:11 blocked for more than 122 seconds.
      Not tainted 6.14.0-rc3-xfstests-lockdep #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u8:0    state:D stack:0     pid:11    tgid:11    ppid:2      task_flags:0x4208160 flags:0x00004000
Workqueue: writeback wb_workfn (flush-253:0)
Call Trace:
 <TASK>
 __schedule+0x309/0x8e0
 schedule+0x3a/0x100
 schedule_preempt_disabled+0x15/0x30
 __mutex_lock+0x59a/0xdb0
 __f2fs_write_data_pages+0x3ac/0x400
 do_writepages+0xe8/0x290
 __writeback_single_inode+0x5c/0x360
 writeback_sb_inodes+0x22f/0x570
 wb_writeback+0xb0/0x410
 wb_do_writeback+0x47/0x2f0
 wb_workfn+0x5a/0x1c0
 process_one_work+0x223/0x5b0
 worker_thread+0x1d5/0x3c0
 kthread+0xfd/0x230
 ret_from_fork+0x31/0x50
 ret_from_fork_asm+0x1a/0x30
 </TASK>

The root cause is: once generic/475 starts toload error table to dm
device, f2fs_prepare_compress_overwrite() will loop reading compressed
cluster pages due to IO error, meanwhile it has held .writepages lock,
it can block all other writeback tasks.

Let's fix this issue w/ below changes:
- add f2fs_handle_page_eio() in prepare_compress_overwrite() to
detect IO error.
- detect cp_error earler in f2fs_read_multi_pages().

Fixes: 4c8ff7095bef ("f2fs: support data compression")
Reported-by: Jan Prusakowski <jprusakowski@google.com>
Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/f2fs/compress.c |  1 +
 fs/f2fs/data.c     | 10 ++++++----
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 985690d81a82..9b94810675c1 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1150,6 +1150,7 @@ static int prepare_compress_overwrite(struct compress_ctx *cc,
 		f2fs_compress_ctx_add_page(cc, page_folio(page));
 
 		if (!PageUptodate(page)) {
+			f2fs_handle_page_eio(sbi, page_folio(page), DATA);
 release_and_retry:
 			f2fs_put_rpages(cc);
 			f2fs_unlock_rpages(cc, i + 1);
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index f1554a5a3d7a..09437dbd1b42 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2190,6 +2190,12 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
 	int i;
 	int ret = 0;
 
+	if (unlikely(f2fs_cp_error(sbi))) {
+		ret = -EIO;
+		from_dnode = false;
+		goto out_put_dnode;
+	}
+
 	f2fs_bug_on(sbi, f2fs_cluster_is_empty(cc));
 
 	last_block_in_file = F2FS_BYTES_TO_BLK(f2fs_readpage_limit(inode) +
@@ -2233,10 +2239,6 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
 	if (ret)
 		goto out;
 
-	if (unlikely(f2fs_cp_error(sbi))) {
-		ret = -EIO;
-		goto out_put_dnode;
-	}
 	f2fs_bug_on(sbi, dn.data_blkaddr != COMPRESS_ADDR);
 
 skip_reading_dnode:
-- 
2.48.1



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