f2fs: finish previous checkpoints before returning from remount

Flush remaining checkpoint requests at the end of remount, since a new
checkpoint would be triggered while remount and we need to take care of
it before returning from remount, in order to avoid the below race
condition.

  - Thread                          - checkpoint thread
  do_remount()
   down_write(&sb->s_umount);
   f2fs_remount()
    f2fs_disable_checkpoint(sbi) -> add checkpoints to the list
                                    block_operations()
                                     down_read_trylock(&sb->s_umount) = 0
   up_write(&sb->s_umount);
                                     f2fs_quota_sync()
                                      dquot_writeback_dquots()
                                       WARN_ON_ONCE(!rwsem_is_locked(&sb->s_umount));

Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index d2eafb56af81c6ce07ea8e310be52f75aa996e73..f266cc385d71fe8c43e4114af9d060673316c3ac 100644 (file)
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2319,9 +2319,9 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
        unsigned long old_sb_flags;
        int err;
        bool need_restart_gc = false, need_stop_gc = false;
-       bool need_restart_ckpt = false, need_stop_ckpt = false;
        bool need_restart_flush = false, need_stop_flush = false;
        bool need_restart_discard = false, need_stop_discard = false;
+       bool need_enable_checkpoint = false, need_disable_checkpoint = false;
        bool no_read_extent_cache = !test_opt(sbi, READ_EXTENT_CACHE);
        bool no_age_extent_cache = !test_opt(sbi, AGE_EXTENT_CACHE);
        bool enable_checkpoint = !test_opt(sbi, DISABLE_CHECKPOINT);
@@ -2485,24 +2485,6 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
                clear_sbi_flag(sbi, SBI_IS_CLOSE);
        }
 
-       if ((*flags & SB_RDONLY) || test_opt(sbi, DISABLE_CHECKPOINT) ||
-                       !test_opt(sbi, MERGE_CHECKPOINT)) {
-               f2fs_stop_ckpt_thread(sbi);
-               need_restart_ckpt = true;
-       } else {
-               /* Flush if the prevous checkpoint, if exists. */
-               f2fs_flush_ckpt_thread(sbi);
-
-               err = f2fs_start_ckpt_thread(sbi);
-               if (err) {
-                       f2fs_err(sbi,
-                           "Failed to start F2FS issue_checkpoint_thread (%d)",
-                           err);
-                       goto restore_gc;
-               }
-               need_stop_ckpt = true;
-       }
-
        /*
         * We stop issue flush thread if FS is mounted as RO
         * or if flush_merge is not passed in mount option.
@@ -2514,7 +2496,7 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
        } else {
                err = f2fs_create_flush_cmd_control(sbi);
                if (err)
-                       goto restore_ckpt;
+                       goto restore_gc;
                need_stop_flush = true;
        }
 
@@ -2536,8 +2518,31 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
                        err = f2fs_disable_checkpoint(sbi);
                        if (err)
                                goto restore_discard;
+                       need_enable_checkpoint = true;
                } else {
                        f2fs_enable_checkpoint(sbi);
+                       need_disable_checkpoint = true;
+               }
+       }
+
+       /*
+        * Place this routine at the end, since a new checkpoint would be
+        * triggered while remount and we need to take care of it before
+        * returning from remount.
+        */
+       if ((*flags & SB_RDONLY) || test_opt(sbi, DISABLE_CHECKPOINT) ||
+                       !test_opt(sbi, MERGE_CHECKPOINT)) {
+               f2fs_stop_ckpt_thread(sbi);
+       } else {
+               /* Flush if the prevous checkpoint, if exists. */
+               f2fs_flush_ckpt_thread(sbi);
+
+               err = f2fs_start_ckpt_thread(sbi);
+               if (err) {
+                       f2fs_err(sbi,
+                           "Failed to start F2FS issue_checkpoint_thread (%d)",
+                           err);
+                       goto restore_checkpoint;
                }
        }
 
@@ -2555,6 +2560,13 @@ skip:
        adjust_unusable_cap_perc(sbi);
        *flags = (*flags & ~SB_LAZYTIME) | (sb->s_flags & SB_LAZYTIME);
        return 0;
+restore_checkpoint:
+       if (need_enable_checkpoint) {
+               f2fs_enable_checkpoint(sbi);
+       } else if (need_disable_checkpoint) {
+               if (f2fs_disable_checkpoint(sbi))
+                       f2fs_warn(sbi, "checkpoint has not been disabled");
+       }
 restore_discard:
        if (need_restart_discard) {
                if (f2fs_start_discard_thread(sbi))
@@ -2570,13 +2582,6 @@ restore_flush:
                clear_opt(sbi, FLUSH_MERGE);
                f2fs_destroy_flush_cmd_control(sbi, false);
        }
-restore_ckpt:
-       if (need_restart_ckpt) {
-               if (f2fs_start_ckpt_thread(sbi))
-                       f2fs_warn(sbi, "background ckpt thread has stopped");
-       } else if (need_stop_ckpt) {
-               f2fs_stop_ckpt_thread(sbi);
-       }
 restore_gc:
        if (need_restart_gc) {
                if (f2fs_start_gc_thread(sbi))