[PATCH 8/8] f2fs: fix to avoid deadlock between checkpoint and writepages

[Chao Yu]

This patch fixes to move f2fs_balance_fs out of sbi->writepages'
coverage to avoid potential ABBA deadlock which was found by lockdep:

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&sbi->writepages);
                                lock(&sbi->cp_mutex);
                                lock(&sbi->writepages);
   lock(&sbi->cp_mutex);

  *** DEADLOCK ***

stack of CPU0:
[<ffffffff810b8dd1>] __lock_acquire+0x1321/0x1770
[<ffffffff810b92d7>] lock_acquire+0xb7/0x130
[<ffffffff817ad082>] mutex_lock_nested+0x52/0x380
[<ffffffffa07b767b>] f2fs_balance_fs+0x8b/0xa0 [f2fs]
[<ffffffffa07afb5b>] f2fs_write_data_page+0x33b/0x460 [f2fs]
[<ffffffffa07ab79a>] __f2fs_writepage+0x1a/0x50 [f2fs]
[<ffffffffa07ac693>] T.1541+0x293/0x560 [f2fs]
[<ffffffffa07aca8c>] f2fs_write_data_pages+0x12c/0x230 [f2fs]
[<ffffffff8118adb3>] do_writepages+0x23/0x40
[<ffffffff8117c545>] __filemap_fdatawrite_range+0xb5/0xf0
[<ffffffff8117c623>] filemap_write_and_wait_range+0xa3/0xd0
[<ffffffffa079cc20>] f2fs_symlink+0x180/0x300 [f2fs]
[<ffffffff81208187>] vfs_symlink+0xb7/0xe0
[<ffffffff8120acc5>] SyS_symlinkat+0xc5/0x100
[<ffffffff81205ad6>] SyS_symlink+0x16/0x20
[<ffffffff817b15d7>] entry_SYSCALL_64_fastpath+0x12/0x6f

stack of CPU1
[<ffffffff810b92d7>] lock_acquire+0xb7/0x130
[<ffffffff817ad082>] mutex_lock_nested+0x52/0x380
[<ffffffffa07aca7e>] f2fs_write_data_pages+0x11e/0x230 [f2fs]
[<ffffffff8118adb3>] do_writepages+0x23/0x40
[<ffffffff8117c545>] __filemap_fdatawrite_range+0xb5/0xf0
[<ffffffff8117c9ef>] filemap_fdatawrite+0x1f/0x30
[<ffffffffa07a728d>] sync_dirty_inodes+0x4d/0xd0 [f2fs]
[<ffffffffa07a7381>] block_operations+0x71/0x160 [f2fs]
[<ffffffffa07a85f8>] write_checkpoint+0xe8/0xbb0 [f2fs]
[<ffffffffa07a043f>] f2fs_sync_fs+0x8f/0xf0 [f2fs]
[<ffffffffa07b63af>] f2fs_balance_fs_bg+0x6f/0xd0 [f2fs]
[<ffffffffa07b1c97>] f2fs_write_node_pages+0x57/0x150 [f2fs]
[<ffffffff8118adb3>] do_writepages+0x23/0x40
[<ffffffff8122c9ed>] __writeback_single_inode+0x6d/0x3d0
[<ffffffff8122ec87>] writeback_sb_inodes+0x2c7/0x520
[<ffffffff8122f193>] wb_writeback+0x133/0x330
[<ffffffff8122f478>] wb_do_writeback+0xe8/0x270
[<ffffffff8122f680>] wb_workfn+0x80/0x1f0
[<ffffffff81081a1c>] process_one_work+0x20c/0x5c0
[<ffffffff81083c62>] worker_thread+0x132/0x5f0
[<ffffffff8108918e>] kthread+0xde/0x100
[<ffffffff817b193f>] ret_from_fork+0x3f/0x70

Signed-off-by: Chao Yu <chao2.yu@xxxxxxxxxxx>
---
 fs/f2fs/data.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 2e97057..985671d 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -506,7 +506,6 @@ static void __allocate_data_blocks(struct inode *inode, loff_t offset,
 	u64 end_offset;
 
 	while (len) {
-		f2fs_balance_fs(sbi);
 		f2fs_lock_op(sbi);
 
 		/* When reading holes, we need its node page */
@@ -1186,7 +1185,7 @@ out:
 	if (err)
 		ClearPageUptodate(page);
 	unlock_page(page);
-	if (need_balance_fs)
+	if (need_balance_fs && !test_opt(sbi, DATA_FLUSH))
 		f2fs_balance_fs(sbi);
 	if (wbc->for_reclaim) {
 		f2fs_submit_merged_bio(sbi, DATA, WRITE);
@@ -1617,6 +1616,8 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	trace_f2fs_direct_IO_enter(inode, offset, count, rw);
 
 	if (rw == WRITE) {
+		f2fs_balance_fs(sbi);
+
 		if (serialized)
 			mutex_lock(&sbi->writepages);
 		__allocate_data_blocks(inode, offset, count);
-- 
2.6.3


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