Commit 4923954b authored by peterz@infradead.org's avatar peterz@infradead.org Committed by Peter Zijlstra
Browse files

futex: Clarify FUTEX2 flags 



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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarAndré Almeida <andrealmeid@igalia.com>
Link: https://lore.kernel.org/r/20230921105247.507327749@noisy.programming.kicks-ass.net
parent c6f4a900

include/uapi/linux/futex.h

+13 −3
Original line number Diff line number Diff line
@@ -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

kernel/futex/syscalls.c

+3 −4
Original line number Diff line number Diff line
@@ -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;