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btrfs: Annotate unlocked accesses to transaction state

Message ID 20201124144413.3168075-1-nborisov@suse.com (mailing list archive)
State New, archived
Headers show
Series btrfs: Annotate unlocked accesses to transaction state | expand

Commit Message

Nikolay Borisov Nov. 24, 2020, 2:44 p.m. UTC
btrfs_transaction::state is protected by btrfs_fs_info::trans_lock and
all accesses to this variable should be synchornized by it. However,
there are 2 exceptions, namely checking if currently running transaction
has entered its commit phase in start_transaction and in
btrfs_should_end_transaction.

Annotate those 2, unlocked accesses with READ_ONCE respectively. Also
remove the full memory barrier in start_transaction as it provides no
ordering guarantees due to being unpaired. All other accsess  to
transaction state happen under trans_lock being held.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/transaction.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--
2.25.1
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Patch

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index df5687a92798..e5a5c3604a9b 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -695,8 +695,7 @@  start_transaction(struct btrfs_root *root, unsigned int num_items,
 	h->can_flush_pending_bgs = true;
 	INIT_LIST_HEAD(&h->new_bgs);

-	smp_mb();
-	if (cur_trans->state >= TRANS_STATE_COMMIT_START &&
+	if (READ_ONCE(cur_trans->state) >= TRANS_STATE_COMMIT_START &&
 	    may_wait_transaction(fs_info, type)) {
 		current->journal_info = h;
 		btrfs_commit_transaction(h);
@@ -912,7 +911,7 @@  int btrfs_should_end_transaction(struct btrfs_trans_handle *trans)
 {
 	struct btrfs_transaction *cur_trans = trans->transaction;

-	if (cur_trans->state >= TRANS_STATE_COMMIT_START ||
+	if (READ_ONCE(cur_trans->state) >= TRANS_STATE_COMMIT_START ||
 	    test_bit(BTRFS_DELAYED_REFS_FLUSHING,
 		     &cur_trans->delayed_refs.flags))
 		return 1;