[v5,10/22] riscv: Fix Race conditions in pthread cancellation [BZ#12683]

Message ID 20230410204614.4129551-2-adhemerval.zanella@linaro.org
State Superseded
Headers
Series Fix Race conditions in pthread cancellation [BZ#12683] |

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent

Commit Message

Adhemerval Zanella Netto April 10, 2023, 8:46 p.m. UTC
  By adding the required syscall_cancel.S.

Reviewed-by: Andrew Waterman <aswaterman@gmail.com>
---
 .../unix/sysv/linux/riscv/syscall_cancel.S    | 67 +++++++++++++++++++
 1 file changed, 67 insertions(+)
 create mode 100644 sysdeps/unix/sysv/linux/riscv/syscall_cancel.S
  

Comments

Xi Ruoyao April 11, 2023, 6:35 a.m. UTC | #1
On Mon, 2023-04-10 at 17:46 -0300, Adhemerval Zanella via Libc-alpha
wrote:
> +1:
> +       addi    sp, sp, -16
> +       cfi_def_cfa_offset (16)
> +       REG_S   ra, (16-SZREG)(sp)
> +       cfi_offset (ra, -SZREG)
> +       call    __syscall_do_cancel

Similarly to LoongArch, IMO this should simply be
"tail __syscall_do_cancel".

Apparently _Noreturn is preventing GCC from generating a tail call for
RISC-V and LoongArch, so if you modeled the assembly following the GCC
output you'll get these sub-optimal things.  It seems a GCC bug to me.
  
Xi Ruoyao April 11, 2023, 7:01 a.m. UTC | #2
On Tue, 2023-04-11 at 14:35 +0800, Xi Ruoyao wrote:
> On Mon, 2023-04-10 at 17:46 -0300, Adhemerval Zanella via Libc-alpha
> wrote:
> > +1:
> > +       addi    sp, sp, -16
> > +       cfi_def_cfa_offset (16)
> > +       REG_S   ra, (16-SZREG)(sp)
> > +       cfi_offset (ra, -SZREG)
> > +       call    __syscall_do_cancel
> 
> Similarly to LoongArch, IMO this should simply be
> "tail __syscall_do_cancel".
> 
> Apparently _Noreturn is preventing GCC from generating a tail call for
> RISC-V and LoongArch

Actually "everywhere" (but why the AArch64 code seems optimized?)

> so if you modeled the assembly following the GCC
> output you'll get these sub-optimal things.  It seems a GCC bug to me.

It's https://gcc.gnu.org/PR10837 and closed as WONTFIX 20 years ago :(.
And a comment from H.J. complained an impact on Glibc.
  
Adhemerval Zanella Netto April 11, 2023, 1:49 p.m. UTC | #3
On 11/04/23 04:01, Xi Ruoyao wrote:
> On Tue, 2023-04-11 at 14:35 +0800, Xi Ruoyao wrote:
>> On Mon, 2023-04-10 at 17:46 -0300, Adhemerval Zanella via Libc-alpha
>> wrote:
>>> +1:
>>> +       addi    sp, sp, -16
>>> +       cfi_def_cfa_offset (16)
>>> +       REG_S   ra, (16-SZREG)(sp)
>>> +       cfi_offset (ra, -SZREG)
>>> +       call    __syscall_do_cancel
>>
>> Similarly to LoongArch, IMO this should simply be
>> "tail __syscall_do_cancel".
>>
>> Apparently _Noreturn is preventing GCC from generating a tail call for
>> RISC-V and LoongArch
> 
> Actually "everywhere" (but why the AArch64 code seems optimized?)

I hand optimized on some architectures, like x86_64 and aarch64.  For most
of the other architectures I just modeled after compiler generated call.

> 
>> so if you modeled the assembly following the GCC
>> output you'll get these sub-optimal things.  It seems a GCC bug to me.
> 
> It's https://gcc.gnu.org/PR10837 and closed as WONTFIX 20 years ago :(.
> And a comment from H.J. complained an impact on Glibc.
> 
>
  

Patch

diff --git a/sysdeps/unix/sysv/linux/riscv/syscall_cancel.S b/sysdeps/unix/sysv/linux/riscv/syscall_cancel.S
new file mode 100644
index 0000000000..742c748d09
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/syscall_cancel.S
@@ -0,0 +1,67 @@ 
+/* Cancellable syscall wrapper.  Linux/riscv version.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+#include <descr-const.h>
+
+/* long int __syscall_cancel_arch (int *cancelhandling,
+				   __syscall_arg_t nr,
+				   __syscall_arg_t arg1,
+				   __syscall_arg_t arg2,
+				   __syscall_arg_t arg3,
+				   __syscall_arg_t arg4,
+				   __syscall_arg_t arg5,
+				   __syscall_arg_t arg6)  */
+
+#ifdef SHARED
+	.option pic
+#else
+	.option nopic
+#endif
+
+ENTRY (__syscall_cancel_arch)
+
+	.globl __syscall_cancel_arch_start
+__syscall_cancel_arch_start:
+	lw	t1, 0(a0)
+	/* if (*ch & CANCELED_BITMASK)  */
+	andi	t1, t1, TCB_CANCELED_BITMASK
+	bne	t1, zero, 1f
+
+	mv	t3, a1
+	mv	a0, a2
+	mv	a1, a3
+	mv	a2, a4
+	mv	a3, a5
+	mv	a4, a6
+	mv	a5, a7
+	mv	a7, t3
+	scall
+
+	.globl __syscall_cancel_arch_end
+__syscall_cancel_arch_end:
+	ret
+
+1:
+	addi	sp, sp, -16
+	cfi_def_cfa_offset (16)
+	REG_S	ra, (16-SZREG)(sp)
+	cfi_offset (ra, -SZREG)
+	call	__syscall_do_cancel
+
+END (__syscall_cancel_arch)