[PATCH v4 3/5] nohz: cpu_isolated strict mode configurable signal

[Chris Metcalf]

Allow userspace to override the default SIGKILL delivered
when a cpu_isolated process in STRICT mode does a syscall
or otherwise synchronously enters the kernel.

In addition to being able to set the signal, we now also
pass whether or not the interruption was from a syscall in
the si_code field of the siginfo.

Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
---
 include/uapi/linux/prctl.h |  2 ++
 kernel/time/tick-sched.c   | 15 +++++++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 0c11238a84fb..ab45bd3d5799 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -195,5 +195,7 @@ struct prctl_mm_map {
 #define PR_GET_CPU_ISOLATED	48
 # define PR_CPU_ISOLATED_ENABLE	(1 << 0)
 # define PR_CPU_ISOLATED_STRICT	(1 << 1)
+# define PR_CPU_ISOLATED_SET_SIG(sig)  (((sig) & 0x7f) << 8)
+# define PR_CPU_ISOLATED_GET_SIG(bits) (((bits) >> 8) & 0x7f)
 
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 9f495c7c7dc2..c5eca9c99fad 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -447,11 +447,18 @@ void tick_nohz_cpu_isolated_enter(void)
 	}
 }
 
-static void kill_cpu_isolated_strict_task(void)
+static void kill_cpu_isolated_strict_task(int is_syscall)
 {
+	siginfo_t info = {};
+	int sig;
+
 	dump_stack();
 	current->cpu_isolated_flags &= ~PR_CPU_ISOLATED_ENABLE;
-	send_sig(SIGKILL, current, 1);
+
+	sig = PR_CPU_ISOLATED_GET_SIG(current->cpu_isolated_flags) ?: SIGKILL;
+	info.si_signo = sig;
+	info.si_code = is_syscall;
+	send_sig_info(sig, &info, current);
 }
 
 /*
@@ -470,7 +477,7 @@ void tick_nohz_cpu_isolated_syscall(int syscall)
 
 	pr_warn("%s/%d: cpu_isolated strict mode violated by syscall %d\n",
 		current->comm, current->pid, syscall);
-	kill_cpu_isolated_strict_task();
+	kill_cpu_isolated_strict_task(1);
 }
 
 /*
@@ -481,7 +488,7 @@ void tick_nohz_cpu_isolated_exception(void)
 {
 	pr_warn("%s/%d: cpu_isolated strict mode violated by exception\n",
 		current->comm, current->pid);
-	kill_cpu_isolated_strict_task();
+	kill_cpu_isolated_strict_task(0);
 }
 
 #endif
-- 
2.1.2

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