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um: nommu: add SMP futex operations

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The asm-generic futex implementation only supports UP operations,
and the normal (MMU) implementation from uaccess.c isn't built
nor would it work.

Since NOMMU shares address space anyway, it's all trivial and we
can just make a trivial implementation.

Link: https://patch.msgid.link/20260723113633.d8373755f77c.I0a83e5ca6be6c95a81d4b2ec69677bbea5889d7d@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
This commit is contained in:
Johannes Berg 2026-07-23 11:35:48 +02:00
parent f979f93c1c
commit 282d0be410
1 changed files with 50 additions and 1 deletions
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51
arch/um/include/asm/futex.h
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@ -12,7 +12,56 @@ int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
u32 oldval, u32 newval);
#else
#include <linux/atomic.h>
#include <asm-generic/futex.h>
#endif
#ifdef CONFIG_SMP
static inline int
arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
{
u32 oldval, newval;
u32 *p = (u32 __force *)uaddr;
do {
oldval = READ_ONCE(*p);
switch (op) {
case FUTEX_OP_SET:
newval = oparg;
break;
case FUTEX_OP_ADD:
newval = oldval + oparg;
break;
case FUTEX_OP_OR:
newval = oldval | oparg;
break;
case FUTEX_OP_ANDN:
newval = oldval & ~oparg;
break;
case FUTEX_OP_XOR:
newval = oldval ^ oparg;
break;
default:
return -ENOSYS;
}
} while (!try_cmpxchg(p, &oldval, newval));
*oval = oldval;
return 0;
}
static inline int
futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
u32 oldval, u32 newval)
{
u32 *p = (u32 __force *)uaddr;
*uval = cmpxchg(p, oldval, newval);
return 0;
}
#endif /* CONFIG_SMP */
#endif /* CONFIG_MMU */
#endif