[PATCH 7/7] f2fs: cache: fix to initialize f2fs_writeback info at mount time

[Chao Yu]

From: Chao Yu <chao@xxxxxxxxxx>

f2fs_start_cache_wb_thread() initializes cache_wb_wq and f2fs_writeback
tunables every time f2fs_writeback thread is started, e.g. in remount,
which causes below race conditions:

1. cache_wb_interval, cache_wb_dirty_threshold and
   cache_wb_total_threshold configured via sysfs will be reset to
   default value after remount.

2. remount will reinitialize cache_wb_wq, which may be used by another
   thread, e.g. f2fs_wake_up_cache_wb(), concurrently.

Let's introduce f2fs_init_cache_wb_info() to initialize them only once
in f2fs_fill_super(), then f2fs_start_cache_wb_thread() only needs to
reset cache_wb_throttled, and READ_ONCE()/WRITE_ONCE() is enough for
cache_wb_task.

Cc: stable@xxxxxxxxxx
Fixes: f45afeabd5df ("f2fs: cache: introduce writeback thread")
Fixes: eeadc4807c95 ("f2fs: cache: wake up f2fs_writeback when exceeding threshold")
Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
---
 fs/f2fs/cache.c | 23 ++++++++++++++---------
 fs/f2fs/cache.h |  1 +
 fs/f2fs/super.c |  1 +
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/fs/f2fs/cache.c b/fs/f2fs/cache.c
index ddf94b5791e7..6cac7662fc1a 100644
--- a/fs/f2fs/cache.c
+++ b/fs/f2fs/cache.c
@@ -844,8 +844,7 @@ void f2fs_wake_up_cache_wb(struct f2fs_sb_info *sbi)
 {
 	struct f2fs_cache_kthread *cache_thread = &sbi->cache_thread;
 
-	/* pairs with smp_store_release() in f2fs_start_cache_wb_thread() */
-	if (!smp_load_acquire(&cache_thread->cache_wb_task))
+	if (!READ_ONCE(cache_thread->cache_wb_task))
 		return;
 
 	if (!f2fs_should_wake_up_cache_wb(sbi))
@@ -855,6 +854,17 @@ void f2fs_wake_up_cache_wb(struct f2fs_sb_info *sbi)
 		wake_up(&cache_thread->cache_wb_wq);
 }
 
+void f2fs_init_cache_wb_info(struct f2fs_sb_info *sbi)
+{
+	struct f2fs_cache_kthread *cache_thread = &sbi->cache_thread;
+
+	init_waitqueue_head(&cache_thread->cache_wb_wq);
+	cache_thread->cache_wb_interval = DEF_DIRTY_CACHE_TIMEOUT;
+	cache_thread->cache_wb_dirty_threshold = DEF_CACHE_WB_DIRTY_THRESH;
+	cache_thread->cache_wb_total_threshold = 0;
+	cache_thread->cache_wb_throttled = false;
+}
+
 int f2fs_start_cache_wb_thread(struct f2fs_sb_info *sbi)
 {
 	struct f2fs_cache_kthread *cache_thread = &sbi->cache_thread;
@@ -865,11 +875,7 @@ int f2fs_start_cache_wb_thread(struct f2fs_sb_info *sbi)
 	if (cache_thread->cache_wb_task)
 		return 0;
 
-	init_waitqueue_head(&cache_thread->cache_wb_wq);
-	cache_thread->cache_wb_interval = DEF_DIRTY_CACHE_TIMEOUT;
-	cache_thread->cache_wb_dirty_threshold = DEF_CACHE_WB_DIRTY_THRESH;
-	cache_thread->cache_wb_total_threshold = 0;
-	cache_thread->cache_wb_throttled = false;
+	WRITE_ONCE(cache_thread->cache_wb_throttled, false);
 	snprintf(name, sizeof(name), "f2fs_writeback-%u:%u",
 			MAJOR(dev), MINOR(dev));
 
@@ -877,8 +883,7 @@ int f2fs_start_cache_wb_thread(struct f2fs_sb_info *sbi)
 	if (IS_ERR(task))
 		return PTR_ERR(task);
 
-	/* pairs with smp_load_acquire() in f2fs_wake_up_cache_wb() */
-	smp_store_release(&cache_thread->cache_wb_task, task);
+	WRITE_ONCE(cache_thread->cache_wb_task, task);
 	return 0;
 }
 
diff --git a/fs/f2fs/cache.h b/fs/f2fs/cache.h
index 5408727dd321..cd017c1b188f 100644
--- a/fs/f2fs/cache.h
+++ b/fs/f2fs/cache.h
@@ -245,6 +245,7 @@ struct f2fs_cache_kthread {
 	bool cache_wb_throttled;	/* last round made no progress */
 };
 
+void f2fs_init_cache_wb_info(struct f2fs_sb_info *sbi);
 int f2fs_start_cache_wb_thread(struct f2fs_sb_info *sbi);
 void f2fs_stop_cache_wb_thread(struct f2fs_sb_info *sbi);
 void f2fs_wake_up_cache_wb(struct f2fs_sb_info *sbi);
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index ba2ec6123251..12a051ba51ac 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -5356,6 +5356,7 @@ static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
 	f2fs_init_cache(sbi, META_CACHE(sbi), F2FS_META_CACHE);
 	f2fs_init_cache(sbi, NODE_CACHE(sbi), F2FS_NODE_CACHE);
 	f2fs_init_cache(sbi, COMPRESS_CACHE(sbi), F2FS_COMPRESS_CACHE);
+	f2fs_init_cache_wb_info(sbi);
 
 	err = f2fs_get_valid_checkpoint(sbi);
 	if (err) {
-- 
2.49.0