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SubjectRe: [PATCH 04/10] Protect kref_put with the lock
On Mon, Jul 22, 2019 at 05:14:20PM +0200, Maksym Planeta wrote:
> Need to ensure that kref_put does not run concurrently with the loop
> inside rxe_pool_get_key.
>
> Signed-off-by: Maksym Planeta <mplaneta@os.inf.tu-dresden.de>
> drivers/infiniband/sw/rxe/rxe_pool.c | 18 ++++++++++++++++++
> drivers/infiniband/sw/rxe/rxe_pool.h | 4 +---
> 2 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/infiniband/sw/rxe/rxe_pool.c b/drivers/infiniband/sw/rxe/rxe_pool.c
> index efa9bab01e02..30a887cf9200 100644
> +++ b/drivers/infiniband/sw/rxe/rxe_pool.c
> @@ -536,3 +536,21 @@ void *rxe_pool_get_key(struct rxe_pool *pool, void *key)
> read_unlock_irqrestore(&pool->pool_lock, flags);
> return node ? elem : NULL;
> }
> +
> +static void rxe_dummy_release(struct kref *kref)
> +{
> +}
> +
> +void rxe_drop_ref(struct rxe_pool_entry *pelem)
> +{
> + int res;
> + struct rxe_pool *pool = pelem->pool;
> + unsigned long flags;
> +
> + write_lock_irqsave(&pool->pool_lock, flags);
> + res = kref_put(&pelem->ref_cnt, rxe_dummy_release);
> + write_unlock_irqrestore(&pool->pool_lock, flags);

This doesn't make sense..

If something is making the kref go to 0 while the node is still in the
RB tree then that is a bug.

You should never need to add locking around a kref_put.

Jason

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