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SubjectRe: [PATCH] mm/mempolicy: Convert from atomic_t to refcount_t on mempolicy->refcnt
On 21-07-19 16:34:28, Xiyu Yang wrote:
> refcount_t type and corresponding API can protect refcounters from
> accidental underflow and overflow and further use-after-free situations.
>
> Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>

lgtm

Acked-by: Ben Widawsky <ben.widawsky@intel.com>

> ---
> include/linux/mempolicy.h | 5 +++--
> mm/mempolicy.c | 8 ++++----
> 2 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
> index 0aaf91b496e2..faec94994eb7 100644
> --- a/include/linux/mempolicy.h
> +++ b/include/linux/mempolicy.h
> @@ -6,6 +6,7 @@
> #ifndef _LINUX_MEMPOLICY_H
> #define _LINUX_MEMPOLICY_H 1
>
> +#include <linux/refcount.h>
> #include <linux/sched.h>
> #include <linux/mmzone.h>
> #include <linux/dax.h>
> @@ -43,7 +44,7 @@ struct mm_struct;
> * to 1, representing the caller of mpol_dup().
> */
> struct mempolicy {
> - atomic_t refcnt;
> + refcount_t refcnt;
> unsigned short mode; /* See MPOL_* above */
> unsigned short flags; /* See set_mempolicy() MPOL_F_* above */
> nodemask_t nodes; /* interleave/bind/perfer */
> @@ -94,7 +95,7 @@ static inline struct mempolicy *mpol_dup(struct mempolicy *pol)
> static inline void mpol_get(struct mempolicy *pol)
> {
> if (pol)
> - atomic_inc(&pol->refcnt);
> + refcount_inc(&pol->refcnt);
> }
>
> extern bool __mpol_equal(struct mempolicy *a, struct mempolicy *b);
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index e32360e90274..829a14f34b43 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -298,7 +298,7 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
> policy = kmem_cache_alloc(policy_cache, GFP_KERNEL);
> if (!policy)
> return ERR_PTR(-ENOMEM);
> - atomic_set(&policy->refcnt, 1);
> + refcount_set(&policy->refcnt, 1);
> policy->mode = mode;
> policy->flags = flags;
>
> @@ -308,7 +308,7 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
> /* Slow path of a mpol destructor. */
> void __mpol_put(struct mempolicy *p)
> {
> - if (!atomic_dec_and_test(&p->refcnt))
> + if (!refcount_dec_and_test(&p->refcnt))
> return;
> kmem_cache_free(policy_cache, p);
> }
> @@ -2290,7 +2290,7 @@ struct mempolicy *__mpol_dup(struct mempolicy *old)
> nodemask_t mems = cpuset_mems_allowed(current);
> mpol_rebind_policy(new, &mems);
> }
> - atomic_set(&new->refcnt, 1);
> + refcount_set(&new->refcnt, 1);
> return new;
> }
>
> @@ -2581,7 +2581,7 @@ static int shared_policy_replace(struct shared_policy *sp, unsigned long start,
> goto alloc_new;
>
> *mpol_new = *n->policy;
> - atomic_set(&mpol_new->refcnt, 1);
> + refcount_set(&mpol_new->refcnt, 1);
> sp_node_init(n_new, end, n->end, mpol_new);
> n->end = start;
> sp_insert(sp, n_new);
> --
> 2.7.4
>

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