| Message ID | 20200709083333.137927-1-wqu@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/2] btrfs: avoid possible signal interruption for btrfs_drop_snapshot() on relocation tree | expand |
On Thu, Jul 09, 2020 at 04:33:32PM +0800, Qu Wenruo wrote: > 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. Could you please rephrase the text above?
On 2020/7/9 下午7:05, David Sterba wrote: > On Thu, Jul 09, 2020 at 04:33:32PM +0800, Qu Wenruo wrote: > >> 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. > > Could you please rephrase the text above? > How about this: As btrfs_join_transaction() won't reserve new metadata space, it won't get interrupted by signal at all. Thanks, Qu
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;
[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(-)