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Commit 90c711ab authored by Zygo Blaxell's avatar Zygo Blaxell Committed by David Sterba
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btrfs: avoid blocking open_ctree from cleaner_kthread 



This fixes a problem introduced in commit 2f3165ec
"btrfs: don't force mounts to wait for cleaner_kthread to delete one or more subvolumes".

open_ctree eventually calls btrfs_replay_log which in turn calls
btrfs_commit_super which tries to lock the cleaner_mutex, causing a
recursive mutex deadlock during mount.

Instead of playing whack-a-mole trying to keep up with all the
functions that may want to lock cleaner_mutex, put all the cleaner_mutex
lockers back where they were, and attack the problem more directly:
keep cleaner_kthread asleep until the filesystem is mounted.

When filesystems are mounted read-only and later remounted read-write,
open_ctree did not set fs_info->open and neither does anything else.
Set this flag in btrfs_remount so that neither btrfs_delete_unused_bgs
nor cleaner_kthread get confused by the common case of "/" filesystem
read-only mount followed by read-write remount.

Signed-off-by: default avatarZygo Blaxell <ce3g8jdj@umail.furryterror.org>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 3b6571c1

fs/btrfs/disk-io.c

+10 −15
Original line number Diff line number Diff line
@@ -1806,6 +1806,13 @@ static int cleaner_kthread(void *arg) 
		if (btrfs_need_cleaner_sleep(root))

			goto sleep;



		/*

		 * Do not do anything if we might cause open_ctree() to block

		 * before we have finished mounting the filesystem.

		 */

		if (!root->fs_info->open)

			goto sleep;



		if (!mutex_trylock(&root->fs_info->cleaner_mutex))

			goto sleep;
@@ -2520,7 +2527,6 @@ int open_ctree(struct super_block *sb, 
	int num_backups_tried = 0;

	int backup_index = 0;

	int max_active;

	bool cleaner_mutex_locked = false;



	tree_root = fs_info->tree_root = btrfs_alloc_root(fs_info, GFP_KERNEL);

	chunk_root = fs_info->chunk_root = btrfs_alloc_root(fs_info, GFP_KERNEL);
@@ -2999,13 +3005,6 @@ int open_ctree(struct super_block *sb, 
		goto fail_sysfs;

	}



	/*

	 * Hold the cleaner_mutex thread here so that we don't block

	 * for a long time on btrfs_recover_relocation.  cleaner_kthread

	 * will wait for us to finish mounting the filesystem.

	 */

	mutex_lock(&fs_info->cleaner_mutex);

	cleaner_mutex_locked = true;

	fs_info->cleaner_kthread = kthread_run(cleaner_kthread, tree_root,

					       "btrfs-cleaner");

	if (IS_ERR(fs_info->cleaner_kthread))
@@ -3065,8 +3064,10 @@ int open_ctree(struct super_block *sb, 
		ret = btrfs_cleanup_fs_roots(fs_info);

		if (ret)

			goto fail_qgroup;

		/* We locked cleaner_mutex before creating cleaner_kthread. */



		mutex_lock(&fs_info->cleaner_mutex);

		ret = btrfs_recover_relocation(tree_root);

		mutex_unlock(&fs_info->cleaner_mutex);

		if (ret < 0) {

			btrfs_warn(fs_info, "failed to recover relocation: %d",

					ret);
@@ -3074,8 +3075,6 @@ int open_ctree(struct super_block *sb, 
			goto fail_qgroup;

		}

	}

	mutex_unlock(&fs_info->cleaner_mutex);

	cleaner_mutex_locked = false;



	location.objectid = BTRFS_FS_TREE_OBJECTID;

	location.type = BTRFS_ROOT_ITEM_KEY;
@@ -3189,10 +3188,6 @@ int open_ctree(struct super_block *sb, 
	filemap_write_and_wait(fs_info->btree_inode->i_mapping);



fail_sysfs:

	if (cleaner_mutex_locked) {

		mutex_unlock(&fs_info->cleaner_mutex);

		cleaner_mutex_locked = false;

	}

	btrfs_sysfs_remove_mounted(fs_info);



fail_fsdev_sysfs:

fs/btrfs/super.c

+2 −0
Original line number Diff line number Diff line
@@ -1807,6 +1807,8 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data) 
			}

		}

		sb->s_flags &= ~MS_RDONLY;



		fs_info->open = 1;

	}

out:

	wake_up_process(fs_info->transaction_kthread);