[PATCH 0/2] Fix data race with transaction->state

[Josef Bacik <josef@toxicpanda.com>]

I've been setting up Claude to setup fstests and run vms automatically and I
kept hitting hangs. This turned out to be a bug with qemu's microvm, but at some
point I was convinced there was a deadlock with running out of block tags and
ordered extent completion and transaction commit. This actually wasn't the case,
however this data race is in fact real. We can easily miss wakeups if we have to
wait on transaction state to change because we do it outside of a lock and we do
not have proper barriers around transaction->state. I suspect this explains the
random hangs that I would see in production while at Meta that would clear up
eventually (we do call wakeup on the transaction wait thing a lot). In any case
this is a data race, even if it wasn't my particular bug, we should fix it.
I've run it through fstests a few times, but obviously spot check it since I'm a
little rusty with this stuff at the moment. Thanks,

Josef

Josef Bacik (2):
  btrfs: fix data race on transaction->state
  btrfs: remove useless smp_mb in start_transaction

 fs/btrfs/disk-io.c     |  8 ++++----
 fs/btrfs/qgroup.c      |  2 +-
 fs/btrfs/transaction.c | 29 +++++++++++++++--------------
 fs/btrfs/volumes.c     |  3 ++-
 4 files changed, 22 insertions(+), 20 deletions(-)

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2.51.1