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rhashtable: Fix potential deadlock by moving schedule_work outside lock
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Move the hash table growth check and work scheduling outside the
rht lock to prevent a possible circular locking dependency.

The original implementation could trigger a lockdep warning due to
a potential deadlock scenario involving nested locks between
rhashtable bucket, rq lock, and dsq lock. By relocating the
growth check and work scheduling after releasing the rth lock, we break
this potential deadlock chain.

This change expands the flexibility of rhashtable by removing
restrictive locking that previously limited its use in scheduler
and workqueue contexts.

Import to say that this calls rht_grow_above_75(), which reads from
struct rhashtable without holding the lock, if this is a problem, we can
move the check to the lock, and schedule the workqueue after the lock.

Fixes: f0e1a06 ("sched_ext: Implement BPF extensible scheduler class")
Suggested-by: Tejun Heo <[email protected]>
Signed-off-by: Breno Leitao <[email protected]>
Signed-off-by: NipaLocal <nipa@local>
leitao authored and NipaLocal committed Nov 28, 2024
1 parent 5115cca commit ff340fa
Showing 1 changed file with 3 additions and 3 deletions.
6 changes: 3 additions & 3 deletions lib/rhashtable.c
Original file line number Diff line number Diff line change
@@ -585,9 +585,6 @@ static struct bucket_table *rhashtable_insert_one(
rht_assign_locked(bkt, obj);

atomic_inc(&ht->nelems);
if (rht_grow_above_75(ht, tbl))
schedule_work(&ht->run_work);

return NULL;
}

@@ -624,6 +621,9 @@ static void *rhashtable_try_insert(struct rhashtable *ht, const void *key,
data = ERR_CAST(new_tbl);

rht_unlock(tbl, bkt, flags);
if (rht_grow_above_75(ht, tbl))
schedule_work(&ht->run_work);

}
} while (!IS_ERR_OR_NULL(new_tbl));

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