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bcachefs: Ensure bch2_btree_node_lock_write_nofail() never fails

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In order for bch2_btree_node_lock_write_nofail() to never produce a
deadlock, we must ensure we're never holding read locks when using it.
Fortunately, it's only used from code paths where any read locks may be
safely dropped.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2023-03-06 08:58:02 -05:00
parent 0d7009d7ca
commit 2ec254c098
2 changed files with 38 additions and 8 deletions
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34
fs/bcachefs/btree_locking.c
View File

@ -320,6 +320,40 @@ int __bch2_btree_node_lock_write(struct btree_trans *trans, struct btree_path *p
return ret;
}
void bch2_btree_node_lock_write_nofail(struct btree_trans *trans,
struct btree_path *path,
struct btree_bkey_cached_common *b)
{
struct btree_path *linked;
unsigned i;
int ret;
/*
* XXX BIG FAT NOTICE
*
* Drop all read locks before taking a write lock:
*
* This is a hack, because bch2_btree_node_lock_write_nofail() is a
* hack - but by dropping read locks first, this should never fail, and
* we only use this in code paths where whatever read locks we've
* already taken are no longer needed:
*/
trans_for_each_path(trans, linked) {
if (!linked->nodes_locked)
continue;
for (i = 0; i < BTREE_MAX_DEPTH; i++)
if (btree_node_read_locked(linked, i)) {
btree_node_unlock(trans, linked, i);
btree_path_set_dirty(linked, BTREE_ITER_NEED_RELOCK);
}
}
ret = __btree_node_lock_write(trans, path, b, true);
BUG_ON(ret);
}
/* relock */
static inline bool btree_path_get_locks(struct btree_trans *trans,

12
fs/bcachefs/btree_locking.h
View File

@ -290,14 +290,6 @@ static inline int __btree_node_lock_write(struct btree_trans *trans,
: __bch2_btree_node_lock_write(trans, path, b, lock_may_not_fail);
}
static inline void bch2_btree_node_lock_write_nofail(struct btree_trans *trans,
struct btree_path *path,
struct btree_bkey_cached_common *b)
{
int ret = __btree_node_lock_write(trans, path, b, true);
BUG_ON(ret);
}
static inline int __must_check
bch2_btree_node_lock_write(struct btree_trans *trans,
struct btree_path *path,
@ -306,6 +298,10 @@ bch2_btree_node_lock_write(struct btree_trans *trans,
return __btree_node_lock_write(trans, path, b, false);
}
void bch2_btree_node_lock_write_nofail(struct btree_trans *,
struct btree_path *,
struct btree_bkey_cached_common *);
/* relock: */
bool bch2_btree_path_relock_norestart(struct btree_trans *,