From: Qu Wenruo <wqu@suse.com>
To: linux-btrfs@vger.kernel.org
Cc: Josef Bacik <josef@toxicpanda.com>
Subject: [PATCH v2 1/2] btrfs: avoid possible signal interruption for btrfs_drop_snapshot() on relocation tree
Date: Thu, 9 Jul 2020 16:33:32 +0800 [thread overview]
Message-ID: <20200709083333.137927-1-wqu@suse.com> (raw)
[BUG]
There is a bug report about bad signal timing could lead to read-only
fs during balance:
BTRFS info (device xvdb): balance: start -d -m -s
BTRFS info (device xvdb): relocating block group 73001861120 flags metadata
BTRFS info (device xvdb): found 12236 extents, stage: move data extents
BTRFS info (device xvdb): relocating block group 71928119296 flags data
BTRFS info (device xvdb): found 3 extents, stage: move data extents
BTRFS info (device xvdb): found 3 extents, stage: update data pointers
BTRFS info (device xvdb): relocating block group 60922265600 flags metadata
BTRFS: error (device xvdb) in btrfs_drop_snapshot:5505: errno=-4 unknown
BTRFS info (device xvdb): forced readonly
BTRFS info (device xvdb): balance: ended with status: -4
[CAUSE]
The direct cause is the -EINTR from the following call chain when a
fatal signal is pending:
relocate_block_group()
|- clean_dirty_subvols()
|- btrfs_drop_snapshot()
|- btrfs_start_transaction()
|- btrfs_delayed_refs_rsv_refill()
|- btrfs_reserve_metadata_bytes()
|- __reserve_metadata_bytes()
|- wait_reserve_ticket()
|- prepare_to_wait_event();
|- ticket->error = -EINTR;
Normally this behavior is fine for most btrfs_start_transaction()
callers, as they need to catch the fatal signal and exit asap.
However for balance, especially for the clean_dirty_subvols() case, we're
already doing cleanup works, such -EINTR from btrfs_drop_snapshot()
could cause a lot of unexpected problems.
From the mentioned forced read-only, to later balance error due to half
dropped reloc trees.
[FIX]
Fix this problem by using btrfs_join_transaction() if
btrfs_drop_snapshot() is called from relocation context.
As btrfs_join_transaction() won't wait full tickets, it won't get
interrupted from signal.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
---
fs/btrfs/extent-tree.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index c0bc35f932bf..d8ef48a807d1 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5298,7 +5298,10 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref, int for_reloc)
goto out;
}
- trans = btrfs_start_transaction(tree_root, 0);
+ if (for_reloc)
+ trans = btrfs_join_transaction(tree_root);
+ else
+ trans = btrfs_start_transaction(tree_root, 0);
if (IS_ERR(trans)) {
err = PTR_ERR(trans);
goto out_free;
--
2.27.0
next reply other threads:[~2020-07-09 8:33 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-09 8:33 Qu Wenruo [this message]
2020-07-09 8:33 ` [PATCH v2 2/2] btrfs: relocation: review the call sites which can be interruped by signal Qu Wenruo
2020-07-09 9:54 ` David Sterba
2020-07-09 10:15 ` Qu Wenruo
2020-07-09 10:25 ` David Sterba
2020-07-09 10:46 ` Qu Wenruo
2020-07-09 11:05 ` [PATCH v2 1/2] btrfs: avoid possible signal interruption for btrfs_drop_snapshot() on relocation tree David Sterba
2020-07-09 12:11 ` Qu Wenruo
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