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bcachefs: Fix assertion popping in transaction commit path

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We can't be holding read locks on btree nodes when we go to take write
locks: this would deadlock if another thread is holding an intent lock
on the node we have a read lock on, and it tries to commit and upgrade
to a write lock.

But instead of triggering an assertion, if this happens we can just
upgrade the read lock to an intent lock.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2020-12-16 13:35:16 -05:00 committed by Kent Overstreet
parent f3721e12d0
commit aa8889c07a
1 changed files with 13 additions and 3 deletions
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16
fs/bcachefs/btree_update_leaf.c
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@ -503,6 +503,10 @@ static inline int do_bch2_trans_commit(struct btree_trans *trans,
/*
* Can't be holding any read locks when we go to take write locks:
* another thread could be holding an intent lock on the same node we
* have a read lock on, and it'll block trying to take a write lock
* (because we hold a read lock) and it could be blocking us by holding
* its own read lock (while we're trying to to take write locks).
*
* note - this must be done after bch2_trans_journal_preres_get_cold()
* or anything else that might call bch2_trans_relock(), since that
@ -510,9 +514,15 @@ static inline int do_bch2_trans_commit(struct btree_trans *trans,
*/
trans_for_each_iter(trans, iter) {
if (iter->nodes_locked != iter->nodes_intent_locked) {
EBUG_ON(iter->flags & BTREE_ITER_KEEP_UNTIL_COMMIT);
EBUG_ON(trans->iters_live & (1ULL << iter->idx));
bch2_btree_iter_unlock_noinline(iter);
if ((iter->flags & BTREE_ITER_KEEP_UNTIL_COMMIT) ||
(trans->iters_live & (1ULL << iter->idx))) {
if (!bch2_btree_iter_upgrade(iter, 1)) {
trace_trans_restart_upgrade(trans->ip);
return -EINTR;
}
} else {
bch2_btree_iter_unlock_noinline(iter);
}
}
}