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SubjectRe: [RFC PATCH v1 1/4] Increase size of ucounts to atomic_long_t
On Mon, Nov 02, 2020 at 05:50:30PM +0100, Alexey Gladkov wrote:
> In order to be able to use ucounts for rlimits, the size must be increased.
> For example user_struct.mq_bytes (RLIMIT_MSGQUEUE) is unsigned long.

I don't have any issues with this change I just wonder what the exact
reason is. It's not immediately obvious to me.

>
> Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
> ---
> include/linux/user_namespace.h | 4 ++--
> kernel/ucount.c | 14 +++++++-------
> 2 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 6ef1c7109fc4..fc75af812d73 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -86,7 +86,7 @@ struct user_namespace {
> struct ctl_table_header *sysctls;
> #endif
> struct ucounts *ucounts;
> - int ucount_max[UCOUNT_COUNTS];
> + long ucount_max[UCOUNT_COUNTS];
> } __randomize_layout;
>
> struct ucounts {
> @@ -94,7 +94,7 @@ struct ucounts {
> struct user_namespace *ns;
> kuid_t uid;
> int count;
> - atomic_t ucount[UCOUNT_COUNTS];
> + atomic_long_t ucount[UCOUNT_COUNTS];
> };
>
> extern struct user_namespace init_user_ns;
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 11b1596e2542..7b2bca8582ef 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -175,14 +175,14 @@ static void put_ucounts(struct ucounts *ucounts)
> kfree(ucounts);
> }
>
> -static inline bool atomic_inc_below(atomic_t *v, int u)
> +static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
> {
> - int c, old;
> - c = atomic_read(v);
> + long c, old;
> + c = atomic_long_read(v);
> for (;;) {
> if (unlikely(c >= u))
> return false;
> - old = atomic_cmpxchg(v, c, c+1);
> + old = atomic_long_cmpxchg(v, c, c+1);
> if (likely(old == c))
> return true;
> c = old;
> @@ -199,14 +199,14 @@ struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
> int max;
> tns = iter->ns;
> max = READ_ONCE(tns->ucount_max[type]);
> - if (!atomic_inc_below(&iter->ucount[type], max))
> + if (!atomic_long_inc_below(&iter->ucount[type], max))
> goto fail;
> }
> return ucounts;
> fail:
> bad = iter;
> for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
> - atomic_dec(&iter->ucount[type]);
> + atomic_long_dec(&iter->ucount[type]);
>
> put_ucounts(ucounts);
> return NULL;
> @@ -216,7 +216,7 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
> {
> struct ucounts *iter;
> for (iter = ucounts; iter; iter = iter->ns->ucounts) {
> - int dec = atomic_dec_if_positive(&iter->ucount[type]);
> + int dec = atomic_long_dec_if_positive(&iter->ucount[type]);
> WARN_ON_ONCE(dec < 0);
> }
> put_ucounts(ucounts);
> --
> 2.25.4
>

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