[PATCH 3/5] f2fs: avoid stucking GC due to atomic write

[Chao Yu <yuchao0@huawei.com>]

f2fs doesn't allow abuse on atomic write class interface, so except
limiting in-mem pages' total memory usage capacity, we need to limit
atomic-write usage as well when filesystem is seriously fragmented,
otherwise we may run into infinite loop during foreground GC because
target blocks in victim segment are belong to atomic opened file for
long time.

Now, we will detect failure due to atomic write in foreground GC, if
the count exceeds threshold, we will drop all atomic written data in
cache, by this, I expect it can keep our system running safely to
prevent Dos attack.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
 fs/f2fs/f2fs.h    |  1 +
 fs/f2fs/file.c    |  5 +++++
 fs/f2fs/gc.c      | 27 +++++++++++++++++++++++----
 fs/f2fs/gc.h      |  3 +++
 fs/f2fs/segment.c |  1 +
 fs/f2fs/segment.h |  2 ++
 6 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index c1c3a1d11186..3453288d6a71 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -2249,6 +2249,7 @@ enum {
 	FI_EXTRA_ATTR,		/* indicate file has extra attribute */
 	FI_PROJ_INHERIT,	/* indicate file inherits projectid */
 	FI_PIN_FILE,		/* indicate file should not be gced */
+	FI_ATOMIC_REVOKE_REQUEST,/* indicate atomic committed data has been dropped */
 };
 
 static inline void __mark_inode_dirty_flag(struct inode *inode,
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 7c90ded5a431..cddd9aee1bb2 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1698,6 +1698,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
 skip_flush:
 	set_inode_flag(inode, FI_HOT_DATA);
 	set_inode_flag(inode, FI_ATOMIC_FILE);
+	clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
 	f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
 
 	F2FS_I(inode)->inmem_task = current;
@@ -1746,6 +1747,10 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
 		ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 1, false);
 	}
 err_out:
+	if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST)) {
+		clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
+		ret = -EINVAL;
+	}
 	up_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
 	inode_unlock(inode);
 	mnt_drop_write_file(filp);
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index bfb7a4a3a929..495876ca62b6 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -135,6 +135,8 @@ int start_gc_thread(struct f2fs_sb_info *sbi)
 	gc_th->gc_urgent = 0;
 	gc_th->gc_wake= 0;
 
+	gc_th->atomic_file = 0;
+
 	sbi->gc_thread = gc_th;
 	init_waitqueue_head(&sbi->gc_thread->gc_wait_queue_head);
 	sbi->gc_thread->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
@@ -603,7 +605,7 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
  * This can be used to move blocks, aka LBAs, directly on disk.
  */
 static void move_data_block(struct inode *inode, block_t bidx,
-					unsigned int segno, int off)
+				int gc_type, unsigned int segno, int off)
 {
 	struct f2fs_io_info fio = {
 		.sbi = F2FS_I_SB(inode),
@@ -630,8 +632,10 @@ static void move_data_block(struct inode *inode, block_t bidx,
 	if (!check_valid_map(F2FS_I_SB(inode), segno, off))
 		goto out;
 
-	if (f2fs_is_atomic_file(inode))
+	if (f2fs_is_atomic_file(inode)) {
+		F2FS_I_SB(inode)->gc_thread->atomic_file++;
 		goto out;
+	}
 
 	if (f2fs_is_pinned_file(inode)) {
 		f2fs_pin_file_control(inode, true);
@@ -737,8 +741,10 @@ static void move_data_page(struct inode *inode, block_t bidx, int gc_type,
 	if (!check_valid_map(F2FS_I_SB(inode), segno, off))
 		goto out;
 
-	if (f2fs_is_atomic_file(inode))
+	if (f2fs_is_atomic_file(inode)) {
+		F2FS_I_SB(inode)->gc_thread->atomic_file++;
 		goto out;
+	}
 	if (f2fs_is_pinned_file(inode)) {
 		if (gc_type == FG_GC)
 			f2fs_pin_file_control(inode, true);
@@ -900,7 +906,8 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 			start_bidx = start_bidx_of_node(nofs, inode)
 								+ ofs_in_node;
 			if (f2fs_encrypted_file(inode))
-				move_data_block(inode, start_bidx, segno, off);
+				move_data_block(inode, start_bidx, gc_type,
+								segno, off);
 			else
 				move_data_page(inode, start_bidx, gc_type,
 								segno, off);
@@ -1017,6 +1024,8 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
 		.ilist = LIST_HEAD_INIT(gc_list.ilist),
 		.iroot = RADIX_TREE_INIT(GFP_NOFS),
 	};
+	unsigned int last_atomic_file = sbi->gc_thread->atomic_file;
+	unsigned int skipped_round = 0, round = 0;
 
 	trace_f2fs_gc_begin(sbi->sb, sync, background,
 				get_pages(sbi, F2FS_DIRTY_NODES),
@@ -1068,11 +1077,21 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
 		sec_freed++;
 	total_freed += seg_freed;
 
+	if (gc_type == FG_GC) {
+		if (sbi->gc_thread->atomic_file > last_atomic_file)
+			skipped_round++;
+		last_atomic_file = sbi->gc_thread->atomic_file;
+		round++;
+	}
+
 	if (gc_type == FG_GC)
 		sbi->cur_victim_sec = NULL_SEGNO;
 
 	if (!sync) {
 		if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
+			if (skipped_round > MAX_SKIP_ATOMIC_COUNT &&
+				skipped_round * 2 >= round)
+				drop_inmem_pages_all(sbi);
 			segno = NULL_SEGNO;
 			goto gc_more;
 		}
diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
index b0045d4c8d1e..bc1d21d46ae7 100644
--- a/fs/f2fs/gc.h
+++ b/fs/f2fs/gc.h
@@ -39,6 +39,9 @@ struct f2fs_gc_kthread {
 	unsigned int gc_idle;
 	unsigned int gc_urgent;
 	unsigned int gc_wake;
+
+	/* for stuck statistic */
+	unsigned int atomic_file;
 };
 
 struct gc_inode_list {
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index d809f731bfd1..831cefa088bc 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -287,6 +287,7 @@ void drop_inmem_pages_all(struct f2fs_sb_info *sbi)
 	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
 
 	if (inode) {
+		set_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
 		drop_inmem_pages(inode);
 		iput(inode);
 	}
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 492ad0c86fa9..7702b054689c 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -215,6 +215,8 @@ struct segment_allocation {
 #define IS_DUMMY_WRITTEN_PAGE(page)			\
 		(page_private(page) == (unsigned long)DUMMY_WRITTEN_PAGE)
 
+#define MAX_SKIP_ATOMIC_COUNT			16
+
 struct inmem_pages {
 	struct list_head list;
 	struct page *page;
-- 
2.15.0.55.gc2ece9dc4de6