[PATCH 3/5] kernel: add support for TIF_NOTIFY_SIGNAL
From: Jens Axboe
Date: Thu Oct 15 2020 - 09:17:19 EST
This adds TIF_NOTIFY_SIGNAL handling in the generic code, which if set,
will return true if signal_pending() is used in a wait loop. That causes
an exit of the loop so that notify_signal tracehooks can be run. If the
wait loop is currently inside a system call, the system call is restarted
once task_work has been processed.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
arch/x86/kernel/signal.c | 2 +-
include/linux/entry-common.h | 9 +++++++--
include/linux/entry-kvm.h | 4 ++--
include/linux/sched/signal.h | 11 ++++++++++-
include/linux/tracehook.h | 27 +++++++++++++++++++++++++++
kernel/entry/common.c | 6 +++---
kernel/entry/kvm.c | 3 +++
7 files changed, 53 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index be0d7d4152ec..d18304e84c09 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -804,7 +804,7 @@ static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
* want to handle. Thus you cannot kill init even with a SIGKILL even by
* mistake.
*/
-void arch_do_signal(struct pt_regs *regs)
+void arch_do_signal(struct pt_regs *regs, unsigned long ti_work)
{
struct ksignal ksig;
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index 159c7476b11b..42e899b3b4a1 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -37,6 +37,10 @@
# define _TIF_UPROBE (0)
#endif
+#ifndef _TIF_NOTIFY_SIGNAL
+# define _TIF_NOTIFY_SIGNAL (0)
+#endif
+
/*
* TIF flags handled in syscall_enter_from_usermode()
*/
@@ -69,7 +73,7 @@
#define EXIT_TO_USER_MODE_WORK \
(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
- _TIF_NEED_RESCHED | _TIF_PATCH_PENDING | \
+ _TIF_NEED_RESCHED | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \
ARCH_EXIT_TO_USER_MODE_WORK)
/**
@@ -261,10 +265,11 @@ static __always_inline void arch_exit_to_user_mode(void) { }
/**
* arch_do_signal - Architecture specific signal delivery function
* @regs: Pointer to currents pt_regs
+ * @ti_work: task thread info work flags
*
* Invoked from exit_to_user_mode_loop().
*/
-void arch_do_signal(struct pt_regs *regs);
+void arch_do_signal(struct pt_regs *regs, unsigned long ti_work);
/**
* arch_syscall_exit_tracehook - Wrapper around tracehook_report_syscall_exit()
diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h
index 0cef17afb41a..9b93f8584ff7 100644
--- a/include/linux/entry-kvm.h
+++ b/include/linux/entry-kvm.h
@@ -11,8 +11,8 @@
# define ARCH_XFER_TO_GUEST_MODE_WORK (0)
#endif
-#define XFER_TO_GUEST_MODE_WORK \
- (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
+#define XFER_TO_GUEST_MODE_WORK \
+ (_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL | \
_TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK)
struct kvm_vcpu;
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 404145dc536e..b2ecc34284b0 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -360,6 +360,15 @@ static inline int task_sigpending(struct task_struct *p)
static inline int signal_pending(struct task_struct *p)
{
+#if defined(CONFIG_GENERIC_ENTRY) && defined(TIF_NOTIFY_SIGNAL)
+ /*
+ * TIF_NOTIFY_SIGNAL isn't really a signal, but it requires the same
+ * behavior in terms of ensuring that we break out of wait loops
+ * so that notify signal callbacks can be processed.
+ */
+ if (unlikely(test_tsk_thread_flag(p, TIF_NOTIFY_SIGNAL)))
+ return 1;
+#endif
return task_sigpending(p);
}
@@ -507,7 +516,7 @@ extern int set_user_sigmask(const sigset_t __user *umask, size_t sigsetsize);
static inline void restore_saved_sigmask_unless(bool interrupted)
{
if (interrupted)
- WARN_ON(!test_thread_flag(TIF_SIGPENDING));
+ WARN_ON(!signal_pending(current));
else
restore_saved_sigmask();
}
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index b480e1a07ed8..0a5bb866e7a6 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -198,4 +198,31 @@ static inline void tracehook_notify_resume(struct pt_regs *regs)
blkcg_maybe_throttle_current();
}
+/*
+ * called by exit_to_user_mode_loop() if ti_work & _TIF_NOTIFY_SIGNAL. This
+ * is currently used by TWA_SIGNAL based task_work, which requires breaking
+ * wait loops to ensure that task_work is noticed and run.
+ */
+static inline void tracehook_notify_signal(void)
+{
+#if defined(CONFIG_GENERIC_ENTRY) && defined(TIF_NOTIFY_SIGNAL)
+ clear_thread_flag(TIF_NOTIFY_SIGNAL);
+ smp_mb__after_atomic();
+ if (current->task_works)
+ task_work_run();
+#endif
+}
+
+/*
+ * Called when we have work to process from exit_to_user_mode_loop()
+ */
+static inline void set_notify_signal(struct task_struct *task)
+{
+#if defined(CONFIG_GENERIC_ENTRY) && defined(TIF_NOTIFY_SIGNAL)
+ if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_SIGNAL) &&
+ !wake_up_state(task, TASK_INTERRUPTIBLE))
+ kick_process(task);
+#endif
+}
+
#endif /* <linux/tracehook.h> */
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index d20ab4ac7183..bd3cf6279e94 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -135,7 +135,7 @@ static __always_inline void exit_to_user_mode(void)
}
/* Workaround to allow gradual conversion of architecture code */
-void __weak arch_do_signal(struct pt_regs *regs) { }
+void __weak arch_do_signal(struct pt_regs *regs, unsigned long ti_work) { }
static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
unsigned long ti_work)
@@ -157,8 +157,8 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
if (ti_work & _TIF_PATCH_PENDING)
klp_update_patch_state(current);
- if (ti_work & _TIF_SIGPENDING)
- arch_do_signal(regs);
+ if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
+ arch_do_signal(regs, ti_work);
if (ti_work & _TIF_NOTIFY_RESUME) {
tracehook_notify_resume(regs);
diff --git a/kernel/entry/kvm.c b/kernel/entry/kvm.c
index b6678a5e3cf6..49972ee99aff 100644
--- a/kernel/entry/kvm.c
+++ b/kernel/entry/kvm.c
@@ -8,6 +8,9 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
do {
int ret;
+ if (ti_work & _TIF_NOTIFY_SIGNAL)
+ tracehook_notify_signal();
+
if (ti_work & _TIF_SIGPENDING) {
kvm_handle_signal_exit(vcpu);
return -EINTR;
--
2.28.0