The series fixes wrong argument type and improves atomic_long_inc_below
by using atomic_long_try_cmpxchg instead of atomic_long_cmpxchg.
Signed-off-by: Uros Bizjak <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Uros Bizjak (2):
ucount: Fix atomic_long_inc_below argument type
ucount: Use atomic_long_try_cmpxchg in atomic_long_inc_below
kernel/ucount.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)
--
2.37.3
The type of u argument of atomic_long_inc_below should be long
to avoid unwanted truncation to int.
Fixes: f9c82a4ea89c ("Increase size of ucounts to atomic_long_t")
Signed-off-by: Uros Bizjak <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
---
kernel/ucount.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/ucount.c b/kernel/ucount.c
index ee8e57fd6f90..74f5b4959feb 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -212,7 +212,7 @@ void put_ucounts(struct ucounts *ucounts)
}
}
-static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
+static inline bool atomic_long_inc_below(atomic_long_t *v, long u)
{
long c, old;
c = atomic_long_read(v);
--
2.37.3
Use atomic_long_try_cmpxchg instead of
atomic_long_cmpxchg (*ptr, old, new) == old in atomic_long_inc_below.
x86 CMPXCHG instruction returns success in ZF flag, so this change saves
a compare after cmpxchg (and related move instruction in front of cmpxchg).
Also, atomic_long_try_cmpxchg implicitly assigns old *ptr value to "old"
when cmpxchg fails, enabling further code simplifications.
No functional change intended.
Signed-off-by: Uros Bizjak <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
---
kernel/ucount.c | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 74f5b4959feb..2c04589a61ff 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -214,16 +214,14 @@ void put_ucounts(struct ucounts *ucounts)
static inline bool atomic_long_inc_below(atomic_long_t *v, long u)
{
- long c, old;
- c = atomic_long_read(v);
- for (;;) {
+ long c = atomic_long_read(v);
+
+ do {
if (unlikely(c >= u))
return false;
- old = atomic_long_cmpxchg(v, c, c+1);
- if (likely(old == c))
- return true;
- c = old;
- }
+ } while (!atomic_long_try_cmpxchg(v, &c, c+1));
+
+ return true;
}
struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
--
2.37.3
On Mon, Oct 17, 2022 at 04:40:49PM +0200, Uros Bizjak wrote:
> Use atomic_long_try_cmpxchg instead of
> atomic_long_cmpxchg (*ptr, old, new) == old in atomic_long_inc_below.
> x86 CMPXCHG instruction returns success in ZF flag, so this change saves
> a compare after cmpxchg (and related move instruction in front of cmpxchg).
>
> Also, atomic_long_try_cmpxchg implicitly assigns old *ptr value to "old"
> when cmpxchg fails, enabling further code simplifications.
>
> No functional change intended.
>
> Signed-off-by: Uros Bizjak <[email protected]>
> Cc: "Eric W. Biederman" <[email protected]>
Reviewed-by: Alexey Gladkov <[email protected]>
Eric, I think the patch looks good. You already reviewed the previous
version [1]. What do you think about this version?
[1] https://lore.kernel.org/lkml/[email protected]/
> ---
> kernel/ucount.c | 14 ++++++--------
> 1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 74f5b4959feb..2c04589a61ff 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -214,16 +214,14 @@ void put_ucounts(struct ucounts *ucounts)
>
> static inline bool atomic_long_inc_below(atomic_long_t *v, long u)
> {
> - long c, old;
> - c = atomic_long_read(v);
> - for (;;) {
> + long c = atomic_long_read(v);
> +
> + do {
> if (unlikely(c >= u))
> return false;
> - old = atomic_long_cmpxchg(v, c, c+1);
> - if (likely(old == c))
> - return true;
> - c = old;
> - }
> + } while (!atomic_long_try_cmpxchg(v, &c, c+1));
> +
> + return true;
> }
>
> struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
> --
> 2.37.3
>
--
Rgrds, legion