f2fs: fix to access nullified flush_cmd_control pointer

f2fs_sync_file()             remount_ro
 - f2fs_readonly
                               - destroy_flush_cmd_control
 - f2fs_issue_flush
   - no fcc pointer!

So, this patch doesn't free fcc in this case, but just stop its kernel thread
which sends flush commands.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

3 files changed, 29 insertions, 11 deletions

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 35dbab157ec3..137bbf0ae4c6 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -2103,7 +2103,7 @@ void f2fs_balance_fs(struct f2fs_sb_info *, bool);
 void f2fs_balance_fs_bg(struct f2fs_sb_info *);
 int f2fs_issue_flush(struct f2fs_sb_info *);
 int create_flush_cmd_control(struct f2fs_sb_info *);
-void destroy_flush_cmd_control(struct f2fs_sb_info *);
+void destroy_flush_cmd_control(struct f2fs_sb_info *, bool);
 void invalidate_blocks(struct f2fs_sb_info *, block_t);
 bool is_checkpointed_data(struct f2fs_sb_info *, block_t);
 void refresh_sit_entry(struct f2fs_sb_info *, block_t, block_t);
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 8affc5621181..d7d5727fe8b2 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -489,8 +489,13 @@ int f2fs_issue_flush(struct f2fs_sb_info *sbi)
         if (!fcc->dispatch_list)
                 wake_up(&fcc->flush_wait_queue);
 
-        wait_for_completion(&cmd.wait);
-        atomic_dec(&fcc->submit_flush);
+        if (fcc->f2fs_issue_flush) {
+                wait_for_completion(&cmd.wait);
+                atomic_dec(&fcc->submit_flush);
+        } else {
+                llist_del_all(&fcc->issue_list);
+                atomic_set(&fcc->submit_flush, 0);
+        }
 
         return cmd.ret;
 }
@@ -501,6 +506,11 @@ int create_flush_cmd_control(struct f2fs_sb_info *sbi)
         struct flush_cmd_control *fcc;
         int err = 0;
 
+        if (SM_I(sbi)->cmd_control_info) {
+                fcc = SM_I(sbi)->cmd_control_info;
+                goto init_thread;
+        }
+
         fcc = kzalloc(sizeof(struct flush_cmd_control), GFP_KERNEL);
         if (!fcc)
                 return -ENOMEM;
@@ -508,6 +518,7 @@ int create_flush_cmd_control(struct f2fs_sb_info *sbi)
         init_waitqueue_head(&fcc->flush_wait_queue);
         init_llist_head(&fcc->issue_list);
         SM_I(sbi)->cmd_control_info = fcc;
+init_thread:
         fcc->f2fs_issue_flush = kthread_run(issue_flush_thread, sbi,
                                 "f2fs_flush-%u:%u", MAJOR(dev), MINOR(dev));
         if (IS_ERR(fcc->f2fs_issue_flush)) {
@@ -520,14 +531,20 @@ int create_flush_cmd_control(struct f2fs_sb_info *sbi)
         return err;
 }
 
-void destroy_flush_cmd_control(struct f2fs_sb_info *sbi)
+void destroy_flush_cmd_control(struct f2fs_sb_info *sbi, bool free)
 {
         struct flush_cmd_control *fcc = SM_I(sbi)->cmd_control_info;
 
-        if (fcc && fcc->f2fs_issue_flush)
-                kthread_stop(fcc->f2fs_issue_flush);
-        kfree(fcc);
-        SM_I(sbi)->cmd_control_info = NULL;
+        if (fcc && fcc->f2fs_issue_flush) {
+                struct task_struct *flush_thread = fcc->f2fs_issue_flush;
+
+                fcc->f2fs_issue_flush = NULL;
+                kthread_stop(flush_thread);
+        }
+        if (free) {
+                kfree(fcc);
+                SM_I(sbi)->cmd_control_info = NULL;
+        }
 }
 
 static void __locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno,
@@ -2738,7 +2755,7 @@ void destroy_segment_manager(struct f2fs_sb_info *sbi)
 
         if (!sm_info)
                 return;
-        destroy_flush_cmd_control(sbi);
+        destroy_flush_cmd_control(sbi, true);
         destroy_dirty_segmap(sbi);
         destroy_curseg(sbi);
         destroy_free_segmap(sbi);
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 1a526474b332..b62c10d28e06 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1102,8 +1102,9 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
          * or if flush_merge is not passed in mount option.
          */
         if ((*flags & MS_RDONLY) || !test_opt(sbi, FLUSH_MERGE)) {
-                destroy_flush_cmd_control(sbi);
-        } else if (!SM_I(sbi)->cmd_control_info) {
+                clear_opt(sbi, FLUSH_MERGE);
+                destroy_flush_cmd_control(sbi, false);
+        } else {
                 err = create_flush_cmd_control(sbi);
                 if (err)
                         goto restore_gc;