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bcachefs: Mark write locks before taking lock

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six locks are unfair: while a thread is blocked trying to take a write
lock, new read locks will fail. The new deadlock cycle detector makes
use of our existing lock tracing, so we need to tell it we're holding a
write lock before we take the lock for it to work correctly.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet
2022-08-26 14:55:00 -04:00
parent 534a591e4c
commit 546180874a
2 changed files with 16 additions and 4 deletions
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9
fs/bcachefs/btree_locking.h
View File

@@ -271,10 +271,15 @@ static inline void bch2_btree_node_lock_write(struct btree_trans *trans,
EBUG_ON(path->l[b->c.level].lock_seq != b->c.lock.state.seq);
EBUG_ON(!btree_node_intent_locked(path, b->c.level));
/*
* six locks are unfair, and read locks block while a thread wants a
* write lock: thus, we need to tell the cycle detector we have a write
* lock _before_ taking the lock:
*/
mark_btree_node_locked_noreset(path, b->c.level, SIX_LOCK_write);
if (unlikely(!six_trylock_write(&b->c.lock)))
__bch2_btree_node_lock_write(trans, b);
mark_btree_node_locked_noreset(path, b->c.level, SIX_LOCK_write);
}
/* relock: */

11
fs/bcachefs/btree_update_leaf.c
View File

@@ -817,6 +817,13 @@ static inline int trans_lock_write(struct btree_trans *trans)
if (same_leaf_as_prev(trans, i))
continue;
/*
* six locks are unfair, and read locks block while a thread
* wants a write lock: thus, we need to tell the cycle detector
* we have a write lock _before_ taking the lock:
*/
mark_btree_node_locked_noreset(i->path, i->level, SIX_LOCK_write);
if (!six_trylock_write(&insert_l(i)->b->c.lock)) {
if (have_conflicting_read_lock(trans, i->path))
goto fail;
@@ -828,13 +835,13 @@ static inline int trans_lock_write(struct btree_trans *trans)
BUG_ON(ret);
}
mark_btree_node_locked_noreset(i->path, i->level, SIX_LOCK_write);
bch2_btree_node_prep_for_write(trans, i->path, insert_l(i)->b);
}
return 0;
fail:
mark_btree_node_locked_noreset(i->path, i->level, SIX_LOCK_intent);
while (--i >= trans->updates) {
if (same_leaf_as_prev(trans, i))
continue;