Commit df94a342 authored Mar 07, 2025 by Qu Wenruo Committed by David Sterba Mar 18, 2025

btrfs: run btrfs_error_commit_super() early



[BUG]
Even after all the error fixes related the
"ASSERT(list_empty(&fs_info->delayed_iputs));" in close_ctree(), I can
still hit it reliably with my experimental 2K block size.

[CAUSE]
In my case, all the error is triggered after the fs is already in error
status.

I find the following call trace to be the cause of race:

           Main thread                       |     endio_write_workers
---------------------------------------------+---------------------------
close_ctree()                                |
|- btrfs_error_commit_super()                |
|  |- btrfs_cleanup_transaction()            |
|  |  |- btrfs_destroy_all_ordered_extents() |
|  |     |- btrfs_wait_ordered_roots()       |
|  |- btrfs_run_delayed_iputs()              |
|                                            | btrfs_finish_ordered_io()
|                                            | |- btrfs_put_ordered_extent()
|                                            |    |- btrfs_add_delayed_iput()
|- ASSERT(list_empty(delayed_iputs))         |
   !!! Triggered !!!

The root cause is that, btrfs_wait_ordered_roots() only wait for
ordered extents to finish their IOs, not to wait for them to finish and
removed.

[FIX]
Since btrfs_error_commit_super() will flush and wait for all ordered
extents, it should be executed early, before we start flushing the
workqueues.

And since btrfs_error_commit_super() now runs early, there is no need to
run btrfs_run_delayed_iputs() inside it, so just remove the
btrfs_run_delayed_iputs() call from btrfs_error_commit_super().

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent fc5c0c58

fs/btrfs/disk-io.c

+8 −7

Original line number	Diff line number	Diff line
		@@ -4320,6 +4320,14 @@ void __cold close_ctree(struct btrfs_fs_info *fs_info)
		/* clear out the rbtree of defraggable inodes */
		btrfs_cleanup_defrag_inodes(fs_info);

		/*
		* Handle the error fs first, as it will flush and wait for all ordered
		* extents. This will generate delayed iputs, thus we want to handle
		* it first.
		*/
		if (unlikely(BTRFS_FS_ERROR(fs_info)))
		btrfs_error_commit_super(fs_info);

		/*
		* Wait for any fixup workers to complete.
		* If we don't wait for them here and they are still running by the time
		@@ -4423,9 +4431,6 @@ void __cold close_ctree(struct btrfs_fs_info *fs_info)
		btrfs_err(fs_info, "commit super ret %d", ret);
		}

		if (BTRFS_FS_ERROR(fs_info))
		btrfs_error_commit_super(fs_info);

		kthread_stop(fs_info->transaction_kthread);
		kthread_stop(fs_info->cleaner_kthread);

		@@ -4548,10 +4553,6 @@ static void btrfs_error_commit_super(struct btrfs_fs_info *fs_info)
		/* cleanup FS via transaction */
		btrfs_cleanup_transaction(fs_info);

		mutex_lock(&fs_info->cleaner_mutex);
		btrfs_run_delayed_iputs(fs_info);
		mutex_unlock(&fs_info->cleaner_mutex);

		down_write(&fs_info->cleanup_work_sem);
		up_write(&fs_info->cleanup_work_sem);
		}