[PATCH AUTOSEL 5.1 016/141] f2fs: fix to avoid deadloop if data_flush is on

Sasha Levin
2019-07-19T04:33:10Z

From: Chao Yu <yuchao0@huawei.com>

[ Upstream commit 040d2bb318d1aea4f28cc22504b44e446666c86e ]

As Hagbard Celine reported:

[ 615.697824] INFO: task kworker/u16:5:344 blocked for more than 120 seconds.
[ 615.697825] Not tainted 5.0.15-gentoo-f2fslog #4
[ 615.697826] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[ 615.697827] kworker/u16:5 D 0 344 2 0x80000000
[ 615.697831] Workqueue: writeback wb_workfn (flush-259:0)
[ 615.697832] Call Trace:
[ 615.697836] ? __schedule+0x2c5/0x8b0
[ 615.697839] schedule+0x32/0x80
[ 615.697841] schedule_preempt_disabled+0x14/0x20
[ 615.697842] __mutex_lock.isra.8+0x2ba/0x4d0
[ 615.697845] ? log_store+0xf5/0x260
[ 615.697848] f2fs_write_data_pages+0x133/0x320
[ 615.697851] ? trace_hardirqs_on+0x2c/0xe0
[ 615.697854] do_writepages+0x41/0xd0
[ 615.697857] __filemap_fdatawrite_range+0x81/0xb0
[ 615.697859] f2fs_sync_dirty_inodes+0x1dd/0x200
[ 615.697861] f2fs_balance_fs_bg+0x2a7/0x2c0
[ 615.697863] ? up_read+0x5/0x20
[ 615.697865] ? f2fs_do_write_data_page+0x2cb/0x940
[ 615.697867] f2fs_balance_fs+0xe5/0x2c0
[ 615.697869] __write_data_page+0x1c8/0x6e0
[ 615.697873] f2fs_write_cache_pages+0x1e0/0x450
[ 615.697878] f2fs_write_data_pages+0x14b/0x320
[ 615.697880] ? trace_hardirqs_on+0x2c/0xe0
[ 615.697883] do_writepages+0x41/0xd0
[ 615.697885] __filemap_fdatawrite_range+0x81/0xb0
[ 615.697887] f2fs_sync_dirty_inodes+0x1dd/0x200
[ 615.697889] f2fs_balance_fs_bg+0x2a7/0x2c0
[ 615.697891] f2fs_write_node_pages+0x51/0x220
[ 615.697894] do_writepages+0x41/0xd0
[ 615.697897] __writeback_single_inode+0x3d/0x3d0
[ 615.697899] writeback_sb_inodes+0x1e8/0x410
[ 615.697902] __writeback_inodes_wb+0x5d/0xb0
[ 615.697904] wb_writeback+0x28f/0x340
[ 615.697906] ? cpumask_next+0x16/0x20
[ 615.697908] wb_workfn+0x33e/0x420
[ 615.697911] process_one_work+0x1a1/0x3d0
[ 615.697913] worker_thread+0x30/0x380
[ 615.697915] ? process_one_work+0x3d0/0x3d0
[ 615.697916] kthread+0x116/0x130
[ 615.697918] ? kthread_create_worker_on_cpu+0x70/0x70
[ 615.697921] ret_from_fork+0x3a/0x50

There is still deadloop in below condition:

d A
- do_writepages
- f2fs_write_node_pages
- f2fs_balance_fs_bg
- f2fs_sync_dirty_inodes
- f2fs_write_cache_pages
- mutex_lock(&sbi->writepages) -- lock once
- __write_data_page
- f2fs_balance_fs_bg
- f2fs_sync_dirty_inodes
- f2fs_write_data_pages
- mutex_lock(&sbi->writepages) -- lock again

Thread A Thread B
- do_writepages
- f2fs_write_node_pages
- f2fs_balance_fs_bg
- f2fs_sync_dirty_inodes
- .cp_task = current
- f2fs_sync_dirty_inodes
- .cp_task = current
- filemap_fdatawrite
- .cp_task = NULL
- filemap_fdatawrite
- f2fs_write_cache_pages
- enter f2fs_balance_fs_bg since .cp_task is NULL
- .cp_task = NULL

Change as below to avoid this:
- add condition to avoid holding .writepages mutex lock in path
of data flush
- introduce mutex lock sbi.flush_lock to exclude concurrent data
flush in background.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/f2fs/data.c | 3 +++
fs/f2fs/f2fs.h | 1 +
fs/f2fs/segment.c | 4 ++++
fs/f2fs/super.c | 1 +
4 files changed, 9 insertions(+)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 9d3c11e09a03..59262327b5ec 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2231,6 +2231,9 @@ static inline bool __should_serialize_io(struct inode *inode,
return false;
if (IS_NOQUOTA(inode))
return false;
+ /* to avoid deadlock in path of data flush */
+ if (F2FS_I(inode)->cp_task)
+ return false;
if (wbc->sync_mode != WB_SYNC_ALL)
return true;
if (get_dirty_pages(inode) >= SM_I(F2FS_I_SB(inode))->min_seq_blocks)
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index e2cf567dcbd7..2ba2478d0663 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1200,6 +1200,7 @@ struct f2fs_sb_info {
/* for inode management */
struct list_head inode_list[NR_INODE_TYPE]; /* dirty inode list */
spinlock_t inode_lock[NR_INODE_TYPE]; /* for dirty inode list lock */
+ struct mutex flush_lock; /* for flush exclusion */

/* for extent tree cache */
struct radix_tree_root extent_tree_root;/* cache extent cache entries */
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 3d6efbfe180f..e9778f06ac0b 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -546,9 +546,13 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
if (test_opt(sbi, DATA_FLUSH)) {
struct blk_plug plug;

+ mutex_lock(&sbi->flush_lock);
+
blk_start_plug(&plug);
f2fs_sync_dirty_inodes(sbi, FILE_INODE);
blk_finish_plug(&plug);
+
+ mutex_unlock(&sbi->flush_lock);
}
f2fs_sync_fs(sbi->sb, true);
stat_inc_bg_cp_count(sbi->stat_info);
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index f2aaa2cc6b3e..6bc1a15b52ad 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -3261,6 +3261,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
INIT_LIST_HEAD(&sbi->inode_list[i]);
spin_lock_init(&sbi->inode_lock[i]);
}
+ mutex_init(&sbi->flush_lock);

f2fs_init_extent_cache_info(sbi);

--
2.20.1