Messages in this thread | | | Date | Mon, 05 Aug 2019 10:55:00 -0700 (PDT) | Subject | Re: [PATCH v2 2/2] cxgb4: smt: Use refcount_t for refcount | From | David Miller <> |
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From: Chuhong Yuan <hslester96@gmail.com> Date: Fri, 2 Aug 2019 16:35:47 +0800
> refcount_t is better for reference counters since its > implementation can prevent overflows. > So convert atomic_t ref counters to refcount_t. > > Signed-off-by: Chuhong Yuan <hslester96@gmail.com> > --- > Changes in v2: > - Convert refcount from 0-base to 1-base.
The existing code is buggy and should be fixed before you start making conversions to it.
> @@ -111,7 +111,7 @@ static void t4_smte_free(struct smt_entry *e) > */ > void cxgb4_smt_release(struct smt_entry *e) > { > - if (atomic_dec_and_test(&e->refcnt)) > + if (refcount_dec_and_test(&e->refcnt)) > t4_smte_free(e);
This runs without any locking and therefore:
> if (e) { > spin_lock(&e->lock); > - if (!atomic_read(&e->refcnt)) { > - atomic_set(&e->refcnt, 1); > + if (refcount_read(&e->refcnt) == 1) { > + refcount_set(&e->refcnt, 2);
This test is not safe, since the reference count can asynchronously decrement to zero above outside of any locks.
Then you'll need to add locking, and as a result the need to an atomic counter goes away and just a normal int can be used.
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