bcachefs: snapshot_create_lock

Add a new lock for snapshot creation - this addresses a few races with
logged operations and snapshot deletion.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/bcachefs.h b/fs/bcachefs/bcachefs.h
index e9d07f9fa1c0e8f8a1e624fdd42e4ab2a0e2cd19..53ffa88cae16cab4e883459dae1fb61424b3b7ec 100644 (file)
--- a/fs/bcachefs/bcachefs.h
+++ b/fs/bcachefs/bcachefs.h
@@ -746,6 +746,7 @@ struct bch_fs {
        struct snapshot_table __rcu *snapshots;
        size_t                  snapshot_table_size;
        struct mutex            snapshot_table_lock;
+       struct rw_semaphore     snapshot_create_lock;
 
        struct work_struct      snapshot_delete_work;
        struct work_struct      snapshot_wait_for_pagecache_and_delete_work;

diff --git a/fs/bcachefs/fs-ioctl.c b/fs/bcachefs/fs-ioctl.c
index 0679b2f79fd6fdca71b820bac339f4bb4ffe2b3a..6040bd3f077819b41accbc08ac37fa5928d0592d 100644 (file)
--- a/fs/bcachefs/fs-ioctl.c
+++ b/fs/bcachefs/fs-ioctl.c
@@ -318,8 +318,8 @@ err:
        return ret;
 }
 
-static long bch2_ioctl_subvolume_create(struct bch_fs *c, struct file *filp,
-                               struct bch_ioctl_subvolume arg)
+static long __bch2_ioctl_subvolume_create(struct bch_fs *c, struct file *filp,
+                                         struct bch_ioctl_subvolume arg)
 {
        struct inode *dir;
        struct bch_inode_info *inode;
@@ -440,6 +440,16 @@ err1:
        return error;
 }
 
+static long bch2_ioctl_subvolume_create(struct bch_fs *c, struct file *filp,
+                                       struct bch_ioctl_subvolume arg)
+{
+       down_write(&c->snapshot_create_lock);
+       long ret = __bch2_ioctl_subvolume_create(c, filp, arg);
+       up_write(&c->snapshot_create_lock);
+
+       return ret;
+}
+
 static long bch2_ioctl_subvolume_destroy(struct bch_fs *c, struct file *filp,
                                struct bch_ioctl_subvolume arg)
 {

diff --git a/fs/bcachefs/io_misc.c b/fs/bcachefs/io_misc.c
index 32432bdddac46ab18ab04172c2fded5e0bccb148..119834cb8f9ee7f80c10b504ca8602ae5614ac37 100644 (file)
--- a/fs/bcachefs/io_misc.c
+++ b/fs/bcachefs/io_misc.c
@@ -287,9 +287,18 @@ int bch2_truncate(struct bch_fs *c, subvol_inum inum, u64 new_i_size, u64 *i_sec
        op.v.inum       = cpu_to_le64(inum.inum);
        op.v.new_i_size = cpu_to_le64(new_i_size);
 
-       return bch2_trans_run(c,
+       /*
+        * Logged ops aren't atomic w.r.t. snapshot creation: creating a
+        * snapshot while they're in progress, then crashing, will result in the
+        * resume only proceeding in one of the snapshots
+        */
+       down_read(&c->snapshot_create_lock);
+       int ret = bch2_trans_run(c,
                bch2_logged_op_start(trans, &op.k_i) ?:
                __bch2_resume_logged_op_truncate(trans, &op.k_i, i_sectors_delta));
+       up_read(&c->snapshot_create_lock);
+
+       return ret;
 }
 
 /* finsert/fcollapse: */
@@ -491,7 +500,16 @@ int bch2_fcollapse_finsert(struct bch_fs *c, subvol_inum inum,
        op.v.src_offset = cpu_to_le64(offset);
        op.v.pos        = cpu_to_le64(insert ? U64_MAX : offset);
 
-       return bch2_trans_run(c,
+       /*
+        * Logged ops aren't atomic w.r.t. snapshot creation: creating a
+        * snapshot while they're in progress, then crashing, will result in the
+        * resume only proceeding in one of the snapshots
+        */
+       down_read(&c->snapshot_create_lock);
+       int ret = bch2_trans_run(c,
                bch2_logged_op_start(trans, &op.k_i) ?:
                __bch2_resume_logged_op_finsert(trans, &op.k_i, i_sectors_delta));
+       up_read(&c->snapshot_create_lock);
+
+       return ret;
 }

diff --git a/fs/bcachefs/snapshot.c b/fs/bcachefs/snapshot.c
index b8c32d1cbd76e8e7d597ab38cff304bdfcd0e065..4982468bfe1182910fa6a03e3b691bf7ce8be758 100644 (file)
--- a/fs/bcachefs/snapshot.c
+++ b/fs/bcachefs/snapshot.c
@@ -1447,6 +1447,8 @@ int bch2_delete_dead_snapshots(struct bch_fs *c)
                }
        }
 
+       down_write(&c->snapshot_create_lock);
+
        for_each_btree_key(trans, iter, BTREE_ID_snapshots,
                           POS_MIN, 0, k, ret) {
                u32 snapshot = k.k->p.offset;
@@ -1457,6 +1459,9 @@ int bch2_delete_dead_snapshots(struct bch_fs *c)
        }
        bch2_trans_iter_exit(trans, &iter);
 
+       if (ret)
+               goto err_create_lock;
+
        /*
         * Fixing children of deleted snapshots can't be done completely
         * atomically, if we crash between here and when we delete the interior
@@ -1467,14 +1472,14 @@ int bch2_delete_dead_snapshots(struct bch_fs *c)
                                  NULL, NULL, BTREE_INSERT_NOFAIL,
                bch2_fix_child_of_deleted_snapshot(trans, &iter, k, &deleted_interior));
        if (ret)
-               goto err;
+               goto err_create_lock;
 
        darray_for_each(deleted, i) {
                ret = commit_do(trans, NULL, NULL, 0,
                        bch2_snapshot_node_delete(trans, *i));
                if (ret) {
                        bch_err_msg(c, ret, "deleting snapshot %u", *i);
-                       goto err;
+                       goto err_create_lock;
                }
        }
 
@@ -1483,11 +1488,13 @@ int bch2_delete_dead_snapshots(struct bch_fs *c)
                        bch2_snapshot_node_delete(trans, *i));
                if (ret) {
                        bch_err_msg(c, ret, "deleting snapshot %u", *i);
-                       goto err;
+                       goto err_create_lock;
                }
        }
 
        clear_bit(BCH_FS_HAVE_DELETED_SNAPSHOTS, &c->flags);
+err_create_lock:
+       up_write(&c->snapshot_create_lock);
 err:
        darray_exit(&deleted_interior);
        darray_exit(&deleted);

diff --git a/fs/bcachefs/super.c b/fs/bcachefs/super.c
index 1c775695336dae5448f38ff2487c2d752b17b550..0e85c22672be85fb09a1ce51ed457d65ab1d2d5c 100644 (file)
--- a/fs/bcachefs/super.c
+++ b/fs/bcachefs/super.c
@@ -720,6 +720,7 @@ static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
 
        mutex_init(&c->bio_bounce_pages_lock);
        mutex_init(&c->snapshot_table_lock);
+       init_rwsem(&c->snapshot_create_lock);
 
        spin_lock_init(&c->btree_write_error_lock);