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futex: Clarify FUTEX2 flags

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sys_futex_waitv() is part of the futex2 series (the first and only so
far) of syscalls and has a flags field per futex (as opposed to flags
being encoded in the futex op).

This new flags field has a new namespace, which unfortunately isn't
super explicit. Notably it currently takes FUTEX_32 and
FUTEX_PRIVATE_FLAG.

Introduce the FUTEX2 namespace to clarify this

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: André Almeida <andrealmeid@igalia.com>
Link: https://lore.kernel.org/r/20230921105247.507327749@noisy.programming.kicks-ass.net
This commit is contained in:
peterz@infradead.org 2023-09-21 12:45:06 +02:00 committed by Peter Zijlstra
parent c6f4a90022
commit 4923954bbc
2 changed files with 16 additions and 7 deletions
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16
include/uapi/linux/futex.h
View File

@ -44,10 +44,20 @@
FUTEX_PRIVATE_FLAG)
/*
* Flags to specify the bit length of the futex word for futex2 syscalls.
* Currently, only 32 is supported.
* Flags for futex2 syscalls.
*/
#define FUTEX_32 2
/* 0x00 */
/* 0x01 */
#define FUTEX2_SIZE_U32 0x02
/* 0x04 */
/* 0x08 */
/* 0x10 */
/* 0x20 */
/* 0x40 */
#define FUTEX2_PRIVATE FUTEX_PRIVATE_FLAG
/* do not use */
#define FUTEX_32 FUTEX2_SIZE_U32 /* historical accident :-( */
/*
* Max numbers of elements in a futex_waitv array

7
kernel/futex/syscalls.c
View File

@ -183,8 +183,7 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
}
/* Mask of available flags for each futex in futex_waitv list */
#define FUTEXV_WAITER_MASK (FUTEX_32 | FUTEX_PRIVATE_FLAG)
#define FUTEX2_VALID_MASK (FUTEX2_SIZE_U32 | FUTEX2_PRIVATE)
/**
* futex_parse_waitv - Parse a waitv array from userspace
@ -205,10 +204,10 @@ static int futex_parse_waitv(struct futex_vector *futexv,
if (copy_from_user(&aux, &uwaitv[i], sizeof(aux)))
return -EFAULT;
if ((aux.flags & ~FUTEXV_WAITER_MASK) || aux.__reserved)
if ((aux.flags & ~FUTEX2_VALID_MASK) || aux.__reserved)
return -EINVAL;
if (!(aux.flags & FUTEX_32))
if (!(aux.flags & FUTEX2_SIZE_U32))
return -EINVAL;
futexv[i].w.flags = aux.flags;