From: Josef Bacik <josef@toxicpanda.com>
To: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: [PATCH 5/5] btrfs: restart snapshot delete if we have to end the transaction
Date: Fri, 20 Mar 2020 14:34:36 -0400 [thread overview]
Message-ID: <20200320183436.16908-6-josef@toxicpanda.com> (raw)
In-Reply-To: <20200320183436.16908-1-josef@toxicpanda.com>
This is to fully fix the deadlock described in
btrfs: do not resolve backrefs for roots that are being deleted
Holding write locks on our deleted snapshot across trans handles will
just lead to sadness, and our backref lookup code is going to want to
still process dropped snapshots for things like qgroup accounting.
Fix this by simply dropping our path before we restart our transaction,
and picking back up from our drop_progress key. This is less efficient
obviously, but it also doesn't deadlock, so it feels like a reasonable
trade off.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
fs/btrfs/extent-tree.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 2925b3ad77a1..bfb413747283 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5257,6 +5257,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
* already dropped.
*/
set_bit(BTRFS_ROOT_DELETING, &root->state);
+again:
if (btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
level = btrfs_header_level(root->node);
path->nodes[level] = btrfs_lock_root_node(root);
@@ -5269,7 +5270,9 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
btrfs_disk_key_to_cpu(&key, &root_item->drop_progress);
memcpy(&wc->update_progress, &key,
sizeof(wc->update_progress));
+ memcpy(&wc->drop_progress, &key, sizeof(key));
+ wc->drop_level = root_item->drop_level;
level = root_item->drop_level;
BUG_ON(level == 0);
path->lowest_level = level;
@@ -5362,6 +5365,18 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
goto out_end_trans;
}
+ /*
+ * We used to keep the path open until we completed the
+ * snapshot delete. However this can deadlock with
+ * things like backref walking that may want to resolve
+ * references that still point to this deleted root. We
+ * already have the ability to restart snapshot
+ * deletions on mount, so just clear our walk_control,
+ * drop the path, and go to the beginning and re-lookup
+ * our drop_progress key and continue from there.
+ */
+ memset(wc, 0, sizeof(*wc));
+ btrfs_release_path(path);
btrfs_end_transaction_throttle(trans);
if (!for_reloc && btrfs_need_cleaner_sleep(fs_info)) {
btrfs_debug(fs_info,
@@ -5377,6 +5392,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
}
if (block_rsv)
trans->block_rsv = block_rsv;
+ goto again;
}
}
btrfs_release_path(path);
--
2.24.1
next prev parent reply other threads:[~2020-03-20 18:34 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-20 18:34 [PATCH 0/5][v2] Relocation and backref resolution fixes Josef Bacik
2020-03-20 18:34 ` [PATCH 1/5] btrfs: reorder reservation before reloc root selection Josef Bacik
2020-03-20 18:34 ` [PATCH 2/5] btrfs: restart relocate_tree_blocks properly Josef Bacik
2020-03-20 18:34 ` [PATCH 3/5] btrfs: track reloc roots based on their commit_root bytenr Josef Bacik
2020-03-20 18:34 ` [PATCH 4/5] btrfs: do not resolve backrefs for roots that are being deleted Josef Bacik
2020-03-20 18:34 ` Josef Bacik [this message]
2020-03-20 19:39 ` [PATCH 5/5] btrfs: restart snapshot delete if we have to end the transaction David Sterba
2020-10-28 22:51 ` Holger Hoffstätte
2020-11-20 8:48 ` Holger Hoffstätte
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