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 <[email protected]>
---
include/linux/entry-common.h | 6 +++++-
include/linux/entry-kvm.h | 4 ++--
include/linux/sched/signal.h | 19 +++++++++++++++++--
include/linux/tracehook.h | 27 +++++++++++++++++++++++++++
kernel/entry/common.c | 5 ++++-
kernel/entry/kvm.c | 3 +++
6 files changed, 58 insertions(+), 6 deletions(-)
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index ccfcc4769925..0929385b9d8d 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)
/**
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 e6f34d8fbf4d..3117ff205a14 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)
{
+#ifdef 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);
}
@@ -506,10 +515,16 @@ extern int set_user_sigmask(const sigset_t __user *umask, size_t sigsetsize);
static inline void restore_saved_sigmask_unless(bool interrupted)
{
- if (interrupted)
+ if (interrupted) {
+#ifdef TIF_NOTIFY_SIGNAL
+ WARN_ON(!test_thread_flag(TIF_SIGPENDING) &&
+ !test_thread_flag(TIF_NOTIFY_SIGNAL));
+#else
WARN_ON(!test_thread_flag(TIF_SIGPENDING));
- else
+#endif
+ } else {
restore_saved_sigmask();
+ }
}
static inline sigset_t *sigmask_to_save(void)
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index b480e1a07ed8..bec952f51439 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)
+{
+#ifdef 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)
+{
+#ifdef 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 0c0cc3cf3eba..6cf9f4fa0f6e 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -140,7 +140,7 @@ bool __weak arch_do_signal(struct pt_regs *regs) { return true; }
static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
unsigned long ti_work)
{
- bool restart_sys = ti_work & _TIF_SIGPENDING;
+ bool restart_sys = ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL);
/*
* Before returning to user space ensure that all pending work
@@ -159,6 +159,9 @@ 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_NOTIFY_SIGNAL)
+ tracehook_notify_signal();
+
if ((ti_work & _TIF_SIGPENDING) && arch_do_signal(regs))
restart_sys = false;
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
On 10/08, Jens Axboe wrote:
>
> On 10/8/20 7:53 AM, Oleg Nesterov wrote:
> >> --- 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();
> >
> > Can't really comment this change, but to me it would be more safe to
> > simply return -EINTR.
> >
> > Or perhaps even better, treat _TIF_NOTIFY_SIGNAL and _TIF_SIGPENDING
> > equally:
> >
> > - if (ti_work & _TIF_SIGPENDING) {
> > + if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) {
> > kvm_handle_signal_exit(vcpu);
> > return -EINTR;
>
> Not sure I follow your logic here. Why treat it any different than
> NOTIFY_RESUME from this perspective?
Ah, good point, I din't notice that xfer_to_guest_mode_work() handles
TIF_NOTIFY_RESUME.
Thanks, then I think this change is fine.
Oleg.
On 10/05, Jens Axboe wrote:
>
> static inline int signal_pending(struct task_struct *p)
> {
> +#ifdef 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);
> }
perhaps we can add test_tsk_thread_mask() later...
> static inline void restore_saved_sigmask_unless(bool interrupted)
> {
> - if (interrupted)
> + if (interrupted) {
> +#ifdef TIF_NOTIFY_SIGNAL
> + WARN_ON(!test_thread_flag(TIF_SIGPENDING) &&
> + !test_thread_flag(TIF_NOTIFY_SIGNAL));
> +#else
> WARN_ON(!test_thread_flag(TIF_SIGPENDING));
> - else
> +#endif
> + } else {
> restore_saved_sigmask();
> + }
I'd suggest to simply do
- WARN_ON(!test_thread_flag(TIF_SIGPENDING));
+ WARN_ON(!signal_pending(current);
> --- 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();
Can't really comment this change, but to me it would be more safe to
simply return -EINTR.
Or perhaps even better, treat _TIF_NOTIFY_SIGNAL and _TIF_SIGPENDING
equally:
- if (ti_work & _TIF_SIGPENDING) {
+ if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) {
kvm_handle_signal_exit(vcpu);
return -EINTR;
Oleg.
On 10/8/20 7:53 AM, Oleg Nesterov wrote:
> On 10/05, Jens Axboe wrote:
>>
>> static inline int signal_pending(struct task_struct *p)
>> {
>> +#ifdef 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);
>> }
>
> perhaps we can add test_tsk_thread_mask() later...
Yeah would be nice, and I bet there are a lot of cases in the kernel
that test multiple bits like that.
>> static inline void restore_saved_sigmask_unless(bool interrupted)
>> {
>> - if (interrupted)
>> + if (interrupted) {
>> +#ifdef TIF_NOTIFY_SIGNAL
>> + WARN_ON(!test_thread_flag(TIF_SIGPENDING) &&
>> + !test_thread_flag(TIF_NOTIFY_SIGNAL));
>> +#else
>> WARN_ON(!test_thread_flag(TIF_SIGPENDING));
>> - else
>> +#endif
>> + } else {
>> restore_saved_sigmask();
>> + }
>
> I'd suggest to simply do
>
> - WARN_ON(!test_thread_flag(TIF_SIGPENDING));
> + WARN_ON(!signal_pending(current);
Ah yes, that's much better. I'll make the edit.
>> --- 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();
>
> Can't really comment this change, but to me it would be more safe to
> simply return -EINTR.
>
> Or perhaps even better, treat _TIF_NOTIFY_SIGNAL and _TIF_SIGPENDING
> equally:
>
> - if (ti_work & _TIF_SIGPENDING) {
> + if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) {
> kvm_handle_signal_exit(vcpu);
> return -EINTR;
Not sure I follow your logic here. Why treat it any different than
NOTIFY_RESUME from this perspective?
--
Jens Axboe