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Date: Thu, 10 Dec 2020 18:36:44 +0100
From: "Alejandro Colomar (man-pages)" <alx.manpages@...il.com>
To: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Darren Hart <dvhart@...radead.org>,
linux-kernel@...r.kernel.org, linux-man@...r.kernel.org,
linux-api@...r.kernel.org
Subject: Re: [PATCH] futex: Change 'utime' parameter to be 'const ... *'
Hi Thomas & Ingo,
I tested the changes. Everything's OK.
Cheers,
Alex
$ uname -a
Linux debian 5.10.0-rc7+alx3+ #4 SMP Thu Dec 10 18:05:03 CET 2020 x86_64
GNU/Linux
.../linux/tools/testing/selftests/futex$ sudo ./run.sh
[sudo] password for user:
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=0 locked=0 owner=0 timeout=0ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=1 locked=0 owner=0 timeout=0ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=1 locked=1 owner=0 timeout=0ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=1 locked=0 owner=1 timeout=0ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=0 locked=1 owner=0 timeout=0ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=0 locked=0 owner=1 timeout=0ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=1 locked=1 owner=0 timeout=5000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=0 locked=1 owner=0 timeout=5000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=1 locked=1 owner=0 timeout=500000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=0 locked=1 owner=0 timeout=500000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=1 locked=0 owner=0 timeout=5000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=0 locked=0 owner=0 timeout=5000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=1 locked=0 owner=0 timeout=500000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=0 locked=0 owner=0 timeout=500000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=1 locked=0 owner=1 timeout=5000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=0 locked=1 owner=0 timeout=5000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=1 locked=0 owner=1 timeout=500000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=0 locked=1 owner=0 timeout=500000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=1 locked=1 owner=0 timeout=2000000000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi: Test requeue functionality
# Arguments: broadcast=0 locked=1 owner=0 timeout=2000000000ns
ok 1 futex-requeue-pi
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi_mismatched_ops: Detect mismatched requeue_pi operations
ok 1 futex-requeue-pi-mismatched-ops
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_requeue_pi_signal_restart: Test signal handling during requeue_pi
# Arguments: <none>
ok 1 futex-requeue-pi-signal-restart
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_wait_timeout: Block on a futex and wait for timeout
# Arguments: timeout=100000ns
ok 1 futex-wait-timeout
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_wait_wouldblock: Test the unexpected futex value in FUTEX_WAIT
ok 1 futex-wait-wouldblock
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_wait_uninitialized_heap: Test the uninitialized futex value in
FUTEX_WAIT
ok 1 futex-wait-uninitialized-heap
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
TAP version 13
1..1
# futex_wait_private_mapped_file: Test the futex value of private file
mappings in FUTEX_WAIT
ok 1 futex-wait-private-mapped-file
# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
On 11/28/20 1:39 PM, Alejandro Colomar wrote:
> futex(2) says that 'utime' is a pointer to 'const'.
> The implementation doesn't use 'const';
> however, it _never_ modifies the contents of utime.
>
> - futex() either uses 'utime' as a pointer to struct or as a 'u32'.
>
> - In case it's used as a 'u32', it makes a copy of it,
> and of course it is not dereferenced.
>
> - In case it's used as a 'struct __kernel_timespec __user *',
> the pointer is not dereferenced inside the futex() definition,
> and it is only passed to a function: get_timespec64(),
> which accepts a 'const struct __kernel_timespec __user *'.
>
> context:
> ........
>
> [[
> FUTEX(2) Linux Programmer's Manual FUTEX(2)
>
> NAME
> futex - fast user-space locking
>
> SYNOPSIS
> #include <linux/futex.h>
> #include <stdint.h>
> #include <sys/time.h>
>
> long futex(uint32_t *uaddr, int futex_op, uint32_t val,
> const struct timespec *timeout, /* or: uint32_t val2 */
> uint32_t *uaddr2, uint32_t val3);
>
> Note: There is no glibc wrapper for this system call; see
> NOTES.
> ]]
>
> $ sed -n '/SYSCALL_DEFINE.(futex\>/,/^}/p' linux/kernel/futex.c
> SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
> struct __kernel_timespec __user *, utime, u32 __user *, uaddr2,
> u32, val3)
> {
> struct timespec64 ts;
> ktime_t t, *tp = NULL;
> u32 val2 = 0;
> int cmd = op & FUTEX_CMD_MASK;
>
> if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
> cmd == FUTEX_WAIT_BITSET ||
> cmd == FUTEX_WAIT_REQUEUE_PI)) {
> if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
> return -EFAULT;
> if (get_timespec64(&ts, utime))
> return -EFAULT;
> if (!timespec64_valid(&ts))
> return -EINVAL;
>
> t = timespec64_to_ktime(ts);
> if (cmd == FUTEX_WAIT)
> t = ktime_add_safe(ktime_get(), t);
> else if (!(op & FUTEX_CLOCK_REALTIME))
> t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
> tp = &t;
> }
> /*
> * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
> * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
> */
> if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
> cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
> val2 = (u32) (unsigned long) utime;
>
> return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
> }
>
> $ sed -n '/get_timespec64(/,/;/p' linux/include/linux/time.h
> int get_timespec64(struct timespec64 *ts,
> const struct __kernel_timespec __user *uts);
>
> ...
>
> Signed-off-by: Alejandro Colomar <alx.manpages@...il.com>
> ---
>
> Hello Thomas & Ingo,
>
> I'm sorry I couldn't test the change in my computers,
> as there is a bug since Linux 5.7 where I can't boot
> (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=974166).
>
> Alex
>
> kernel/futex.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 00259c7e288e..28577c7d2805 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -3792,8 +3792,8 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
>
>
> SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
> - struct __kernel_timespec __user *, utime, u32 __user *, uaddr2,
> - u32, val3)
> + const struct __kernel_timespec __user *, utime,
> + u32 __user *, uaddr2, u32, val3)
> {
> struct timespec64 ts;
> ktime_t t, *tp = NULL;
>
--
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es
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