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Message-ID: <20230807123322.814039156@infradead.org>
Date: Mon, 07 Aug 2023 14:18:44 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: tglx@...utronix.de, axboe@...nel.dk
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
mingo@...hat.com, dvhart@...radead.org, dave@...olabs.net,
andrealmeid@...lia.com, Andrew Morton <akpm@...ux-foundation.org>,
urezki@...il.com, hch@...radead.org, lstoakes@...il.com,
Arnd Bergmann <arnd@...db.de>, linux-api@...r.kernel.org,
linux-mm@...ck.org, linux-arch@...r.kernel.org,
malteskarupke@....de
Subject: [PATCH v2 01/14] 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: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
---
include/uapi/linux/futex.h | 16 +++++++++++++---
kernel/futex/syscalls.c | 7 +++----
2 files changed, 16 insertions(+), 7 deletions(-)
--- a/include/uapi/linux/futex.h
+++ b/include/uapi/linux/futex.h
@@ -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
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -183,8 +183,7 @@ SYSCALL_DEFINE6(futex, u32 __user *, uad
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 fute
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;
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