[patch 06/12] rseq: Implement sys_rseq_slice_yield()

Thomas Gleixner
2025-09-08T23:00:05Z

Provide a new syscall which has the only purpose to yield the CPU after the
kernel granted a time slice extension.

sched_yield() is not suitable for that because it unconditionally
schedules, but the end of the time slice extension is not required to
schedule when the task was already preempted. This also allows to have a
strict check for termination to catch user space invoking random syscalls
including sched_yield() from a time slice extension region.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-arch@vger.kernel.org
---
arch/alpha/kernel/syscalls/syscall.tbl | 1 +
arch/arm/tools/syscall.tbl | 1 +
arch/arm64/tools/syscall_32.tbl | 1 +
arch/m68k/kernel/syscalls/syscall.tbl | 1 +
arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
arch/mips/kernel/syscalls/syscall_n32.tbl | 1 +
arch/mips/kernel/syscalls/syscall_n64.tbl | 1 +
arch/mips/kernel/syscalls/syscall_o32.tbl | 1 +
arch/parisc/kernel/syscalls/syscall.tbl | 1 +
arch/powerpc/kernel/syscalls/syscall.tbl | 1 +
arch/s390/kernel/syscalls/syscall.tbl | 1 +
arch/sh/kernel/syscalls/syscall.tbl | 1 +
arch/sparc/kernel/syscalls/syscall.tbl | 1 +
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
arch/xtensa/kernel/syscalls/syscall.tbl | 1 +
include/linux/syscalls.h | 1 +
include/uapi/asm-generic/unistd.h | 5 ++++-
kernel/rseq.c | 9 +++++++++
kernel/sys_ni.c | 1 +
scripts/syscall.tbl | 1 +
21 files changed, 32 insertions(+), 1 deletion(-)

--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -509,3 +509,4 @@
577 common open_tree_attr sys_open_tree_attr
578 common file_getattr sys_file_getattr
579 common file_setattr sys_file_setattr
+580 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -484,3 +484,4 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/arm64/tools/syscall_32.tbl
+++ b/arch/arm64/tools/syscall_32.tbl
@@ -481,3 +481,4 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -469,3 +469,4 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -475,3 +475,4 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -408,3 +408,4 @@
467 n32 open_tree_attr sys_open_tree_attr
468 n32 file_getattr sys_file_getattr
469 n32 file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -384,3 +384,4 @@
467 n64 open_tree_attr sys_open_tree_attr
468 n64 file_getattr sys_file_getattr
469 n64 file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -457,3 +457,4 @@
467 o32 open_tree_attr sys_open_tree_attr
468 o32 file_getattr sys_file_getattr
469 o32 file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -468,3 +468,4 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -560,3 +560,4 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 nospu rseq_slice_yield sys_rseq_slice_yield
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -472,3 +472,4 @@
467 common open_tree_attr sys_open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield sys_rseq_slice_yield
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -473,3 +473,4 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -515,3 +515,4 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -475,3 +475,4 @@
467 i386 open_tree_attr sys_open_tree_attr
468 i386 file_getattr sys_file_getattr
469 i386 file_setattr sys_file_setattr
+470 i386 rseq_slice_yield sys_rseq_slice_yield
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -393,6 +393,7 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield

#
# Due to a historical design error, certain syscalls are numbered differently
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -440,3 +440,4 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 common rseq_slice_yield sys_rseq_slice_yield
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -957,6 +957,7 @@ asmlinkage long sys_statx(int dfd, const
unsigned mask, struct statx __user *buffer);
asmlinkage long sys_rseq(struct rseq __user *rseq, uint32_t rseq_len,
int flags, uint32_t sig);
+asmlinkage long sys_rseq_slice_yield(void);
asmlinkage long sys_open_tree(int dfd, const char __user *path, unsigned flags);
asmlinkage long sys_open_tree_attr(int dfd, const char __user *path,
unsigned flags,
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -858,8 +858,11 @@
#define __NR_file_setattr 469
__SYSCALL(__NR_file_setattr, sys_file_setattr)

+#define __NR_rseq_slice_yield 470
+__SYSCALL(__NR_rseq_slice_yield, sys_rseq_slice_yield)
+
#undef __NR_syscalls
-#define __NR_syscalls 470
+#define __NR_syscalls 471

/*
* 32 bit systems traditionally used different
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -542,6 +542,15 @@ int rseq_slice_extension_prctl(unsigned
return -EFAULT;
}

+SYSCALL_DEFINE0(rseq_slice_yield)
+{
+ if (need_resched()) {
+ schedule();
+ return 1;
+ }
+ return 0;
+}
+
static int __init rseq_slice_cmdline(char *str)
{
bool on;
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -390,5 +390,6 @@ COND_SYSCALL(setuid16);

/* restartable sequence */
COND_SYSCALL(rseq);
+COND_SYSCALL(rseq_sched_yield);

COND_SYSCALL(uretprobe);
--- a/scripts/syscall.tbl
+++ b/scripts/syscall.tbl
@@ -410,3 +410,4 @@
467 common open_tree_attr sys_open_tree_attr
468 common file_getattr sys_file_getattr
469 common file_setattr sys_file_setattr
+470 common rseq_sched_yield sys_rseq_sched_yield