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Date: Mon, 7 Aug 2023 21:52:18 -0300
From: André Almeida <andrealmeid@...lia.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, mingo@...hat.com,
dvhart@...radead.org, dave@...olabs.net, tglx@...utronix.de,
Andrew Morton <akpm@...ux-foundation.org>, axboe@...nel.dk,
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: Re: [PATCH v2 03/14] futex: Flag conversion
Em 07/08/2023 09:18, Peter Zijlstra escreveu:
> Futex has 3 sets of flags:
>
> - legacy futex op bits
> - futex2 flags
> - internal flags
>
> Add a few helpers to convert from the API flags into the internal
> flags.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: André Almeida <andrealmeid@...lia.com>
> ---
> kernel/futex/futex.h | 63 +++++++++++++++++++++++++++++++++++++++++++++---
> kernel/futex/syscalls.c | 24 ++++++------------
> kernel/futex/waitwake.c | 4 +--
> 3 files changed, 71 insertions(+), 20 deletions(-)
>
> --- a/kernel/futex/futex.h
> +++ b/kernel/futex/futex.h
> @@ -5,6 +5,7 @@
> #include <linux/futex.h>
> #include <linux/rtmutex.h>
> #include <linux/sched/wake_q.h>
> +#include <linux/compat.h>
>
> #ifdef CONFIG_PREEMPT_RT
> #include <linux/rcuwait.h>
> @@ -16,8 +17,15 @@
> * Futex flags used to encode options to functions and preserve them across
> * restarts.
> */
> +#define FLAGS_SIZE_8 0x00
> +#define FLAGS_SIZE_16 0x01
> +#define FLAGS_SIZE_32 0x02
> +#define FLAGS_SIZE_64 0x03
> +
Minor nit: for consistent, I would go with SIZE_U8, instead of SIZE_8
> +#define FLAGS_SIZE_MASK 0x03
> +
> #ifdef CONFIG_MMU
> -# define FLAGS_SHARED 0x01
> +# define FLAGS_SHARED 0x10
> #else
> /*
> * NOMMU does not have per process address space. Let the compiler optimize
> @@ -25,8 +33,57 @@
> */
> # define FLAGS_SHARED 0x00
> #endif
> -#define FLAGS_CLOCKRT 0x02
> -#define FLAGS_HAS_TIMEOUT 0x04
> +#define FLAGS_CLOCKRT 0x20
> +#define FLAGS_HAS_TIMEOUT 0x40
> +#define FLAGS_NUMA 0x80
> +
> +/* FUTEX_ to FLAGS_ */
> +static inline unsigned int futex_to_flags(unsigned int op)
> +{
> + unsigned int flags = FLAGS_SIZE_32;
> +
> + if (!(op & FUTEX_PRIVATE_FLAG))
> + flags |= FLAGS_SHARED;
> +
> + if (op & FUTEX_CLOCK_REALTIME)
> + flags |= FLAGS_CLOCKRT;
> +
> + return flags;
> +}
> +
> +/* FUTEX2_ to FLAGS_ */
> +static inline unsigned int futex2_to_flags(unsigned int flags2)
> +{
> + unsigned int flags = flags2 & FUTEX2_SIZE_MASK;
> +
> + if (!(flags2 & FUTEX2_PRIVATE))
> + flags |= FLAGS_SHARED;
> +
> + if (flags2 & FUTEX2_NUMA)
> + flags |= FLAGS_NUMA;
> +
> + return flags;
> +}
> +
> +static inline bool futex_flags_valid(unsigned int flags)
> +{
> + /* Only 64bit futexes for 64bit code */
> + if (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall()) {
> + if ((flags & FLAGS_SIZE_MASK) == FLAGS_SIZE_64)
> + return false;
> + }
> +
> + /* Only 32bit futexes are implemented -- for now */
> + if ((flags & FLAGS_SIZE_MASK) != FLAGS_SIZE_32)
> + return false;
> +
> + return true;
> +} > +
> +static inline unsigned int futex_size(unsigned int flags)
> +{
> + return 1 << (flags & FLAGS_SIZE_MASK);
> +}
>
> #ifdef CONFIG_FAIL_FUTEX
> extern bool should_fail_futex(bool fshared);
> --- a/kernel/futex/syscalls.c
> +++ b/kernel/futex/syscalls.c
> @@ -1,6 +1,5 @@
> // SPDX-License-Identifier: GPL-2.0-or-later
>
> -#include <linux/compat.h>
> #include <linux/syscalls.h>
> #include <linux/time_namespace.h>
>
> @@ -85,15 +84,12 @@ SYSCALL_DEFINE3(get_robust_list, int, pi
> long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
> u32 __user *uaddr2, u32 val2, u32 val3)
> {
> + unsigned int flags = futex_to_flags(op);
> int cmd = op & FUTEX_CMD_MASK;
> - unsigned int flags = 0;
>
> - if (!(op & FUTEX_PRIVATE_FLAG))
> - flags |= FLAGS_SHARED;
> -
> - if (op & FUTEX_CLOCK_REALTIME) {
> - flags |= FLAGS_CLOCKRT;
> - if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
> + if (flags & FLAGS_CLOCKRT) {
> + if (cmd != FUTEX_WAIT_BITSET &&
> + cmd != FUTEX_WAIT_REQUEUE_PI &&
> cmd != FUTEX_LOCK_PI2)
> return -ENOSYS;
> }
> @@ -201,21 +197,19 @@ static int futex_parse_waitv(struct fute
> unsigned int i;
>
> for (i = 0; i < nr_futexes; i++) {
> + unsigned int flags;
> +
> if (copy_from_user(&aux, &uwaitv[i], sizeof(aux)))
> return -EFAULT;
>
> if ((aux.flags & ~FUTEX2_VALID_MASK) || aux.__reserved)
> return -EINVAL;
>
> - if (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall()) {
> - if ((aux.flags & FUTEX2_SIZE_MASK) == FUTEX2_SIZE_U64)
> - return -EINVAL;
> - }
> -
> - if ((aux.flags & FUTEX2_SIZE_MASK) != FUTEX2_SIZE_U32)
> + flags = futex2_to_flags(aux.flags);
> + if (!futex_flags_valid(flags))
> return -EINVAL;
>
> - futexv[i].w.flags = aux.flags;
> + futexv[i].w.flags = flags;
> futexv[i].w.val = aux.val;
> futexv[i].w.uaddr = aux.uaddr;
> futexv[i].q = futex_q_init;
> --- a/kernel/futex/waitwake.c
> +++ b/kernel/futex/waitwake.c
> @@ -419,11 +419,11 @@ static int futex_wait_multiple_setup(str
> */
> retry:
> for (i = 0; i < count; i++) {
> - if ((vs[i].w.flags & FUTEX_PRIVATE_FLAG) && retry)
> + if (!(vs[i].w.flags & FLAGS_SHARED) && retry)
> continue;
>
> ret = get_futex_key(u64_to_user_ptr(vs[i].w.uaddr),
> - !(vs[i].w.flags & FUTEX_PRIVATE_FLAG),
> + vs[i].w.flags & FLAGS_SHARED,
> &vs[i].q.key, FUTEX_READ);
>
> if (unlikely(ret))
>
>
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