From: Qu Wenruo wqu@suse.com
commit 6f23277a49e68f8a9355385c846939ad0b1261e7 upstream
[BUG] When running the following script, btrfs will trigger an ASSERT():
#/bin/bash mkfs.btrfs -f $dev mount $dev $mnt xfs_io -f -c "pwrite 0 1G" $mnt/file sync btrfs quota enable $mnt btrfs quota rescan -w $mnt
# Manually set the limit below current usage btrfs qgroup limit 512M $mnt $mnt
# Crash happens touch $mnt/file
The dmesg looks like this:
assertion failed: refcount_read(&trans->use_count) == 1, in fs/btrfs/transaction.c:2022 ------------[ cut here ]------------ kernel BUG at fs/btrfs/ctree.h:3230! invalid opcode: 0000 [#1] SMP PTI RIP: 0010:assertfail.constprop.0+0x18/0x1a [btrfs] btrfs_commit_transaction.cold+0x11/0x5d [btrfs] try_flush_qgroup+0x67/0x100 [btrfs] __btrfs_qgroup_reserve_meta+0x3a/0x60 [btrfs] btrfs_delayed_update_inode+0xaa/0x350 [btrfs] btrfs_update_inode+0x9d/0x110 [btrfs] btrfs_dirty_inode+0x5d/0xd0 [btrfs] touch_atime+0xb5/0x100 iterate_dir+0xf1/0x1b0 __x64_sys_getdents64+0x78/0x110 do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7fb5afe588db
[CAUSE] In try_flush_qgroup(), we assume we don't hold a transaction handle at all. This is true for data reservation and mostly true for metadata. Since data space reservation always happens before we start a transaction, and for most metadata operation we reserve space in start_transaction().
But there is an exception, btrfs_delayed_inode_reserve_metadata(). It holds a transaction handle, while still trying to reserve extra metadata space.
When we hit EDQUOT inside btrfs_delayed_inode_reserve_metadata(), we will join current transaction and commit, while we still have transaction handle from qgroup code.
[FIX] Let's check current->journal before we join the transaction.
If current->journal is unset or BTRFS_SEND_TRANS_STUB, it means we are not holding a transaction, thus are able to join and then commit transaction.
If current->journal is a valid transaction handle, we avoid committing transaction and just end it
This is less effective than committing current transaction, as it won't free metadata reserved space, but we may still free some data space before new data writes.
Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1178634 Fixes: c53e9653605d ("btrfs: qgroup: try to flush qgroup space when we get -EDQUOT") Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Qu Wenruo wqu@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Anand Jain anand.jain@oracle.com --- fs/btrfs/qgroup.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index 2f119adbc808..78146501c665 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -3502,6 +3502,7 @@ static int try_flush_qgroup(struct btrfs_root *root) { struct btrfs_trans_handle *trans; int ret; + bool can_commit = true;
/* * We don't want to run flush again and again, so if there is a running @@ -3513,6 +3514,20 @@ static int try_flush_qgroup(struct btrfs_root *root) return 0; }
+ /* + * If current process holds a transaction, we shouldn't flush, as we + * assume all space reservation happens before a transaction handle is + * held. + * + * But there are cases like btrfs_delayed_item_reserve_metadata() where + * we try to reserve space with one transction handle already held. + * In that case we can't commit transaction, but at least try to end it + * and hope the started data writes can free some space. + */ + if (current->journal_info && + current->journal_info != BTRFS_SEND_TRANS_STUB) + can_commit = false; + ret = btrfs_start_delalloc_snapshot(root); if (ret < 0) goto out; @@ -3524,7 +3539,10 @@ static int try_flush_qgroup(struct btrfs_root *root) goto out; }
- ret = btrfs_commit_transaction(trans); + if (can_commit) + ret = btrfs_commit_transaction(trans); + else + ret = btrfs_end_transaction(trans); out: clear_bit(BTRFS_ROOT_QGROUP_FLUSHING, &root->state); wake_up(&root->qgroup_flush_wait);