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bcachefs: Fix bch2_btree_node_upgrade()

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Previously, if we were trying to upgrade from a read to an intent lock
but we held an additional read lock via another btree_path,
bch2_btree_node_upgrade() would always fail, in six_lock_tryupgrade().

This patch factors out the code that __bch2_btree_node_lock_write() uses
to temporarily drop extra read locks, so that six_lock_tryupgrade() can
succeed.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
This commit is contained in:
Kent Overstreet 2022-08-05 13:06:44 -04:00 committed by Kent Overstreet
parent 845cffed0d
commit 62448afee7
1 changed files with 18 additions and 4 deletions
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22
fs/bcachefs/btree_locking.c
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@ -230,6 +230,7 @@ bool bch2_btree_node_upgrade(struct btree_trans *trans,
struct btree_path *path, unsigned level)
{
struct btree *b = path->l[level].b;
struct six_lock_count count = bch2_btree_node_lock_counts(trans, path, &b->c, level);
if (!is_btree_node(path, level))
return false;
@ -253,11 +254,24 @@ bool bch2_btree_node_upgrade(struct btree_trans *trans,
if (race_fault())
return false;
if (btree_node_locked(path, level)
? six_lock_tryupgrade(&b->c.lock)
: six_relock_type(&b->c.lock, SIX_LOCK_intent, path->l[level].lock_seq))
goto success;
if (btree_node_locked(path, level)) {
bool ret;
six_lock_readers_add(&b->c.lock, -count.n[SIX_LOCK_read]);
ret = six_lock_tryupgrade(&b->c.lock);
six_lock_readers_add(&b->c.lock, count.n[SIX_LOCK_read]);
if (ret)
goto success;
} else {
if (six_relock_type(&b->c.lock, SIX_LOCK_intent, path->l[level].lock_seq))
goto success;
}
/*
* Do we already have an intent lock via another path? If so, just bump
* lock count:
*/
if (btree_node_lock_seq_matches(path, b, level) &&
btree_node_lock_increment(trans, &b->c, level, BTREE_NODE_INTENT_LOCKED)) {
btree_node_unlock(trans, path, level);