| Message ID | 20171031114853.841-2-mbenes@suse.cz (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | [v3,1/2] livepatch: send a fake signal to all blocking tasks | expand |
> +/* > + * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set. > + * Kthreads with TIF_PATCH_PENDING set are woken up. Only admin can request this > + * action currently. > + */ > +void klp_force_signals(void) > +{ > + struct task_struct *g, *task; > + > + pr_notice("signaling remaining tasks\n"); > + > + read_lock(&tasklist_lock); > + for_each_process_thread(g, task) { > + if (!klp_patch_pending(task)) > + continue; > + > + /* > + * There is a small race here. We could see TIF_PATCH_PENDING > + * set and decide to wake up a kthread or send a fake signal. > + * Meanwhile the task could migrate itself and the action > + * would be meaningless. It is not serious though. > + */ > + if (task->flags & PF_KTHREAD) { > + /* > + * Wake up a kthread which still has not been migrated. > + */ > + wake_up_process(task); So this is not as safe as one would hope. It tries to wake all TASK_NORMAL tasks, which could cause headaches. Let's make it wake_up_state(task, TASK_INTERRUPTIBLE); to wake only kthreads sleeping interruptedly. Thanks Petr for spotting this (offline). Miroslav > + } else { > + /* > + * Send fake signal to all non-kthread tasks which are > + * still not migrated. > + */ > + spin_lock_irq(&task->sighand->siglock); > + signal_wake_up(task, 0); > + spin_unlock_irq(&task->sighand->siglock); > + } > + } > + read_unlock(&tasklist_lock); > +}
On Tue 2017-10-31 12:48:52, Miroslav Benes wrote: > Live patching consistency model is of LEAVE_PATCHED_SET and > SWITCH_THREAD. This means that all tasks in the system have to be marked > one by one as safe to call a new patched function. Safe means when a > task is not (sleeping) in a set of patched functions. That is, no > patched function is on the task's stack. Another clearly safe place is > the boundary between kernel and userspace. The patching waits for all > tasks to get outside of the patched set or to cross the boundary. The > transition is completed afterwards. > > The problem is that a task can block the transition for quite a long > time, if not forever. It could sleep in a set of patched functions, for > example. Luckily we can force the task to leave the set by sending it a > fake signal, that is a signal with no data in signal pending structures > (no handler, no sign of proper signal delivered). Suspend/freezer use > this to freeze the tasks as well. The task gets TIF_SIGPENDING set and > is woken up (if it has been sleeping in the kernel before) or kicked by > rescheduling IPI (if it was running on other CPU). This causes the task > to go to kernel/userspace boundary where the signal would be handled and > the task would be marked as safe in terms of live patching. > > diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c > index b004a1fb6032..6700d3b22615 100644 > --- a/kernel/livepatch/transition.c > +++ b/kernel/livepatch/transition.c > @@ -577,3 +577,43 @@ void klp_copy_process(struct task_struct *child) > > /* TIF_PATCH_PENDING gets copied in setup_thread_stack() */ > } > + > +/* > + * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set. > + * Kthreads with TIF_PATCH_PENDING set are woken up. Only admin can request this > + * action currently. > + */ > +void klp_force_signals(void) > +{ > + struct task_struct *g, *task; > + > + pr_notice("signaling remaining tasks\n"); > + > + read_lock(&tasklist_lock); > + for_each_process_thread(g, task) { > + if (!klp_patch_pending(task)) > + continue; > + > + /* > + * There is a small race here. We could see TIF_PATCH_PENDING > + * set and decide to wake up a kthread or send a fake signal. > + * Meanwhile the task could migrate itself and the action > + * would be meaningless. It is not serious though. > + */ > + if (task->flags & PF_KTHREAD) { > + /* > + * Wake up a kthread which still has not been migrated. > + */ > + wake_up_process(task); I have just noticed that freezer used wake_up_state(p, TASK_INTERRUPTIBLE); IMHO, we should do so as well. wake_up_process() wakes also tasks in TASK_UNINTERRUPTIBLE state. These might not be ready for an unexpected wakeup. For example, see concat_dev_erase() in drivers/mtd/mtdcontact.c. With this change, feel free to use Reviewed-by: Petr Mladek <pmladek@suse.com> Best Regards, Petr
On 11/01, Petr Mladek wrote: > > On Tue 2017-10-31 12:48:52, Miroslav Benes wrote: > > + if (task->flags & PF_KTHREAD) { > > + /* > > + * Wake up a kthread which still has not been migrated. > > + */ > > + wake_up_process(task); > > I have just noticed that freezer used wake_up_state(p, TASK_INTERRUPTIBLE); > IMHO, we should do so as well. I won't argue, but... > wake_up_process() wakes also tasks in TASK_UNINTERRUPTIBLE state. > These might not be ready for an unexpected wakeup. For example, > see concat_dev_erase() in drivers/mtd/mtdcontact.c. I'd say that concat_dev_erase() should be fixed, any code should be ready for spurious wakeup. Note also that wake_up_state(TASK_INTERRUPTIBLE) won't wakeup the TASK_IDLE kthreads, and most of the kthreads which use TASK_INTERRUPTIBLE should use TASK_IDLE today, because in most cases TASK_INTERRUPTIBLE was used to not contribute to loadavg. Oleg.
On Wed, 1 Nov 2017, Oleg Nesterov wrote: > On 11/01, Petr Mladek wrote: > > > > On Tue 2017-10-31 12:48:52, Miroslav Benes wrote: > > > + if (task->flags & PF_KTHREAD) { > > > + /* > > > + * Wake up a kthread which still has not been migrated. > > > + */ > > > + wake_up_process(task); > > > > I have just noticed that freezer used wake_up_state(p, TASK_INTERRUPTIBLE); > > IMHO, we should do so as well. > > I won't argue, but... > > > wake_up_process() wakes also tasks in TASK_UNINTERRUPTIBLE state. > > These might not be ready for an unexpected wakeup. For example, > > see concat_dev_erase() in drivers/mtd/mtdcontact.c. > > I'd say that concat_dev_erase() should be fixed, any code should be ready > for spurious wakeup. I agree. > Note also that wake_up_state(TASK_INTERRUPTIBLE) won't wakeup the TASK_IDLE > kthreads, and most of the kthreads which use TASK_INTERRUPTIBLE should use > TASK_IDLE today, because in most cases TASK_INTERRUPTIBLE was used to not > contribute to loadavg. Yes. Unfortunately, we have TASK_IDLE for more than two years now and nothing much has happened yet. TASK_IDLE is still used sporadically. I'd like to be on the safe side with livepatch and given that TASK_INTERRUPTIBLE loops should be prepared for spurious wakeups by definition, I think it is better to have wake_up_state(TASK_INTERRUPTIBLE) there. At least till all "concat_dev_erase" beauties are fixed (sigh). Miroslav
On Tue, Oct 31, 2017 at 12:48:52PM +0100, Miroslav Benes wrote: > + > +/* > + * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set. > + * Kthreads with TIF_PATCH_PENDING set are woken up. Only admin can request this > + * action currently. > + */ > +void klp_force_signals(void) Since "force" now has a separate meaning, it's a little confusing to have it in the name of this function. How about klp_send_signals() or klp_signal()?
On Tue, Oct 31, 2017 at 12:48:52PM +0100, Miroslav Benes wrote: > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c > index bf8c8fd72589..b7c60662baf3 100644 > --- a/kernel/livepatch/core.c > +++ b/kernel/livepatch/core.c > @@ -440,6 +440,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch); > * /sys/kernel/livepatch/<patch> > * /sys/kernel/livepatch/<patch>/enabled > * /sys/kernel/livepatch/<patch>/transition > + * /sys/kernel/livepatch/<patch>/signal > * /sys/kernel/livepatch/<patch>/<object> > * /sys/kernel/livepatch/<patch>/<object>/<function,sympos> > */ > @@ -514,11 +515,37 @@ static ssize_t transition_show(struct kobject *kobj, > patch == klp_transition_patch); > } > > +static ssize_t signal_store(struct kobject *kobj, struct kobj_attribute *attr, > + const char *buf, size_t count) > +{ > + int ret; > + bool val; > + > + /* > + * klp_mutex lock is not grabbed here intentionally. It is not really > + * needed. The race window is harmless and grabbing the lock would only > + * hold the action back. > + */ > + if (!klp_transition_patch) > + return -EINVAL; > + > + ret = kstrtobool(buf, &val); > + if (ret) > + return ret; > + > + if (val) > + klp_force_signals(); > + > + return count; > +} The function still has global functionality even though the sysfs entry is now per-patch. So if you do echo 1 > /sys/kernel/livepatch/patch1/signal But patch2 is in transition, then it will send signals based on patch2. Instead it should probably return an error. There's a similar issue with force_store().
On 11/02, Miroslav Benes wrote: > > On Wed, 1 Nov 2017, Oleg Nesterov wrote: > > > Note also that wake_up_state(TASK_INTERRUPTIBLE) won't wakeup the TASK_IDLE > > kthreads, and most of the kthreads which use TASK_INTERRUPTIBLE should use > > TASK_IDLE today, because in most cases TASK_INTERRUPTIBLE was used to not > > contribute to loadavg. > > Yes. Unfortunately, we have TASK_IDLE for more than two years now and > nothing much has happened yet. TASK_IDLE is still used sporadically. I'd > like to be on the safe side with livepatch OK, as I said I won't argue, > and given that > TASK_INTERRUPTIBLE loops should be prepared for spurious wakeups by > definition, Not really when it comes to kthreads. Once again, unless kthread does allow_signal() TASK_INTERRUPTIBLE does not really differ from TASK_UNINTERRUPTIBLE except the latter contributes to loadavg. And that is why TASK_INTERRUPTIBLE was commonly used instead of TASK_UNINTERRUPTIBLE, so I do not think that TASK_INTERRUPTIBLE loops are more ready in general than TASK_UNINTERRUPTIBLE. Oleg.
On Thu, 2 Nov 2017, Josh Poimboeuf wrote: > On Tue, Oct 31, 2017 at 12:48:52PM +0100, Miroslav Benes wrote: > > + > > +/* > > + * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set. > > + * Kthreads with TIF_PATCH_PENDING set are woken up. Only admin can request this > > + * action currently. > > + */ > > +void klp_force_signals(void) > > Since "force" now has a separate meaning, it's a little confusing to > have it in the name of this function. How about klp_send_signals() or > klp_signal()? or klp_send_signal()? Miroslav
On Thu, 2 Nov 2017, Josh Poimboeuf wrote: > On Tue, Oct 31, 2017 at 12:48:52PM +0100, Miroslav Benes wrote: > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c > > index bf8c8fd72589..b7c60662baf3 100644 > > --- a/kernel/livepatch/core.c > > +++ b/kernel/livepatch/core.c > > @@ -440,6 +440,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch); > > * /sys/kernel/livepatch/<patch> > > * /sys/kernel/livepatch/<patch>/enabled > > * /sys/kernel/livepatch/<patch>/transition > > + * /sys/kernel/livepatch/<patch>/signal > > * /sys/kernel/livepatch/<patch>/<object> > > * /sys/kernel/livepatch/<patch>/<object>/<function,sympos> > > */ > > @@ -514,11 +515,37 @@ static ssize_t transition_show(struct kobject *kobj, > > patch == klp_transition_patch); > > } > > > > +static ssize_t signal_store(struct kobject *kobj, struct kobj_attribute *attr, > > + const char *buf, size_t count) > > +{ > > + int ret; > > + bool val; > > + > > + /* > > + * klp_mutex lock is not grabbed here intentionally. It is not really > > + * needed. The race window is harmless and grabbing the lock would only > > + * hold the action back. > > + */ > > + if (!klp_transition_patch) > > + return -EINVAL; > > + > > + ret = kstrtobool(buf, &val); > > + if (ret) > > + return ret; > > + > > + if (val) > > + klp_force_signals(); > > + > > + return count; > > +} > > The function still has global functionality even though the sysfs entry > is now per-patch. So if you do > > echo 1 > /sys/kernel/livepatch/patch1/signal > > But patch2 is in transition, then it will send signals based on patch2. > Instead it should probably return an error. > > There's a similar issue with force_store(). Bah. I still find having "signal" and "force" in /sys/kernel/livepatch/<patch>/ a bit odd, but I'll add struct klp_patch *patch; patch = container_of(kobj, struct klp_patch, kobj); /* ... */ if (patch != klp_transition_patch) return -EINVAL; That should solve it for all cases. Thanks, Miroslav
On Fri, Nov 03, 2017 at 09:02:50AM +0100, Miroslav Benes wrote: > On Thu, 2 Nov 2017, Josh Poimboeuf wrote: > > > On Tue, Oct 31, 2017 at 12:48:52PM +0100, Miroslav Benes wrote: > > > + > > > +/* > > > + * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set. > > > + * Kthreads with TIF_PATCH_PENDING set are woken up. Only admin can request this > > > + * action currently. > > > + */ > > > +void klp_force_signals(void) > > > > Since "force" now has a separate meaning, it's a little confusing to > > have it in the name of this function. How about klp_send_signals() or > > klp_signal()? > > or klp_send_signal()? It can send more than one signal, so I'd prefer the plural form: klp_send_signals().
Hi! > --- a/Documentation/ABI/testing/sysfs-kernel-livepatch > +++ b/Documentation/ABI/testing/sysfs-kernel-livepatch > @@ -33,6 +33,15 @@ Contact: live-patching@vger.kernel.org > An attribute which indicates whether the patch is currently in > transition. > > +What: /sys/kernel/livepatch/<patch>/signal > +Date: Oct 2017 > +KernelVersion: 4.15.0 > +Contact: live-patching@vger.kernel.org > +Description: > + A writable attribute that allows administrator to affect the > + course of an existing transition. Writing 1 sends a signal to > + all remaining blocking tasks. What kind of signal? > What: /sys/kernel/livepatch/<patch>/<object> > Date: Nov 2014 > KernelVersion: 3.19.0 > diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt > index ecdb18104ab0..6694530d0894 100644 > --- a/Documentation/livepatch/livepatch.txt > +++ b/Documentation/livepatch/livepatch.txt > @@ -178,6 +178,12 @@ transition, it shows -1. Any tasks which are blocking the transition > can be signaled with SIGSTOP and SIGCONT to force them to change their > patched state. > > +Administrator can also affect a transition through > +/sys/kernel/livepatch/<patch>/signal attribute. Writing 1 to the attribute sends > +a signal to all remaining blocking tasks. This is an alternative for > +SIGSTOP/SIGCONT approach mentioned in the previous paragraph. It should also be > +less harmful to the system. Well... If SIGSTOP / SIGCONT is considered harmful (it probably is), it should be mentioned above, and not in note here... Pavel
diff --git a/Documentation/ABI/testing/sysfs-kernel-livepatch b/Documentation/ABI/testing/sysfs-kernel-livepatch index d5d39748382f..22f6267836c2 100644 --- a/Documentation/ABI/testing/sysfs-kernel-livepatch +++ b/Documentation/ABI/testing/sysfs-kernel-livepatch @@ -33,6 +33,15 @@ Contact: live-patching@vger.kernel.org An attribute which indicates whether the patch is currently in transition. +What: /sys/kernel/livepatch/<patch>/signal +Date: Oct 2017 +KernelVersion: 4.15.0 +Contact: live-patching@vger.kernel.org +Description: + A writable attribute that allows administrator to affect the + course of an existing transition. Writing 1 sends a signal to + all remaining blocking tasks. + What: /sys/kernel/livepatch/<patch>/<object> Date: Nov 2014 KernelVersion: 3.19.0 diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt index ecdb18104ab0..6694530d0894 100644 --- a/Documentation/livepatch/livepatch.txt +++ b/Documentation/livepatch/livepatch.txt @@ -178,6 +178,12 @@ transition, it shows -1. Any tasks which are blocking the transition can be signaled with SIGSTOP and SIGCONT to force them to change their patched state. +Administrator can also affect a transition through +/sys/kernel/livepatch/<patch>/signal attribute. Writing 1 to the attribute sends +a signal to all remaining blocking tasks. This is an alternative for +SIGSTOP/SIGCONT approach mentioned in the previous paragraph. It should also be +less harmful to the system. + 3.1 Adding consistency model support to new architectures --------------------------------------------------------- @@ -435,6 +441,9 @@ Information about the registered patches can be found under /sys/kernel/livepatch. The patches could be enabled and disabled by writing there. +/sys/kernel/livepatch/<patch>/signal attribute allows administrator to affect a +patching operation. + See Documentation/ABI/testing/sysfs-kernel-livepatch for more details. diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c index e9436c5e1e09..bf9c4e7792d1 100644 --- a/arch/powerpc/kernel/signal.c +++ b/arch/powerpc/kernel/signal.c @@ -153,6 +153,9 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags) if (thread_info_flags & _TIF_UPROBE) uprobe_notify_resume(regs); + if (thread_info_flags & _TIF_PATCH_PENDING) + klp_update_patch_state(current); + if (thread_info_flags & _TIF_SIGPENDING) { BUG_ON(regs != current->thread.regs); do_signal(current); @@ -163,9 +166,6 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags) tracehook_notify_resume(regs); } - if (thread_info_flags & _TIF_PATCH_PENDING) - klp_update_patch_state(current); - user_enter(); } diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 03505ffbe1b6..fb90bdb3602f 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -153,6 +153,9 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) if (cached_flags & _TIF_UPROBE) uprobe_notify_resume(regs); + if (cached_flags & _TIF_PATCH_PENDING) + klp_update_patch_state(current); + /* deal with pending signal delivery */ if (cached_flags & _TIF_SIGPENDING) do_signal(regs); @@ -165,9 +168,6 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) if (cached_flags & _TIF_USER_RETURN_NOTIFY) fire_user_return_notifiers(); - if (cached_flags & _TIF_PATCH_PENDING) - klp_update_patch_state(current); - /* Disable IRQs and retry */ local_irq_disable(); diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c index bf8c8fd72589..b7c60662baf3 100644 --- a/kernel/livepatch/core.c +++ b/kernel/livepatch/core.c @@ -440,6 +440,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch); * /sys/kernel/livepatch/<patch> * /sys/kernel/livepatch/<patch>/enabled * /sys/kernel/livepatch/<patch>/transition + * /sys/kernel/livepatch/<patch>/signal * /sys/kernel/livepatch/<patch>/<object> * /sys/kernel/livepatch/<patch>/<object>/<function,sympos> */ @@ -514,11 +515,37 @@ static ssize_t transition_show(struct kobject *kobj, patch == klp_transition_patch); } +static ssize_t signal_store(struct kobject *kobj, struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int ret; + bool val; + + /* + * klp_mutex lock is not grabbed here intentionally. It is not really + * needed. The race window is harmless and grabbing the lock would only + * hold the action back. + */ + if (!klp_transition_patch) + return -EINVAL; + + ret = kstrtobool(buf, &val); + if (ret) + return ret; + + if (val) + klp_force_signals(); + + return count; +} + static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled); static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition); +static struct kobj_attribute signal_kobj_attr = __ATTR_WO(signal); static struct attribute *klp_patch_attrs[] = { &enabled_kobj_attr.attr, &transition_kobj_attr.attr, + &signal_kobj_attr.attr, NULL }; diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c index b004a1fb6032..6700d3b22615 100644 --- a/kernel/livepatch/transition.c +++ b/kernel/livepatch/transition.c @@ -577,3 +577,43 @@ void klp_copy_process(struct task_struct *child) /* TIF_PATCH_PENDING gets copied in setup_thread_stack() */ } + +/* + * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set. + * Kthreads with TIF_PATCH_PENDING set are woken up. Only admin can request this + * action currently. + */ +void klp_force_signals(void) +{ + struct task_struct *g, *task; + + pr_notice("signaling remaining tasks\n"); + + read_lock(&tasklist_lock); + for_each_process_thread(g, task) { + if (!klp_patch_pending(task)) + continue; + + /* + * There is a small race here. We could see TIF_PATCH_PENDING + * set and decide to wake up a kthread or send a fake signal. + * Meanwhile the task could migrate itself and the action + * would be meaningless. It is not serious though. + */ + if (task->flags & PF_KTHREAD) { + /* + * Wake up a kthread which still has not been migrated. + */ + wake_up_process(task); + } else { + /* + * Send fake signal to all non-kthread tasks which are + * still not migrated. + */ + spin_lock_irq(&task->sighand->siglock); + signal_wake_up(task, 0); + spin_unlock_irq(&task->sighand->siglock); + } + } + read_unlock(&tasklist_lock); +} diff --git a/kernel/livepatch/transition.h b/kernel/livepatch/transition.h index ce09b326546c..6c480057539a 100644 --- a/kernel/livepatch/transition.h +++ b/kernel/livepatch/transition.h @@ -10,5 +10,6 @@ void klp_cancel_transition(void); void klp_start_transition(void); void klp_try_complete_transition(void); void klp_reverse_transition(void); +void klp_force_signals(void); #endif /* _LIVEPATCH_TRANSITION_H */ diff --git a/kernel/signal.c b/kernel/signal.c index 800a18f77732..9009b8e77bc3 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -40,6 +40,7 @@ #include <linux/cn_proc.h> #include <linux/compiler.h> #include <linux/posix-timers.h> +#include <linux/livepatch.h> #define CREATE_TRACE_POINTS #include <trace/events/signal.h> @@ -163,7 +164,8 @@ void recalc_sigpending_and_wake(struct task_struct *t) void recalc_sigpending(void) { - if (!recalc_sigpending_tsk(current) && !freezing(current)) + if (!recalc_sigpending_tsk(current) && !freezing(current) && + !klp_patch_pending(current)) clear_thread_flag(TIF_SIGPENDING); }
Live patching consistency model is of LEAVE_PATCHED_SET and SWITCH_THREAD. This means that all tasks in the system have to be marked one by one as safe to call a new patched function. Safe means when a task is not (sleeping) in a set of patched functions. That is, no patched function is on the task's stack. Another clearly safe place is the boundary between kernel and userspace. The patching waits for all tasks to get outside of the patched set or to cross the boundary. The transition is completed afterwards. The problem is that a task can block the transition for quite a long time, if not forever. It could sleep in a set of patched functions, for example. Luckily we can force the task to leave the set by sending it a fake signal, that is a signal with no data in signal pending structures (no handler, no sign of proper signal delivered). Suspend/freezer use this to freeze the tasks as well. The task gets TIF_SIGPENDING set and is woken up (if it has been sleeping in the kernel before) or kicked by rescheduling IPI (if it was running on other CPU). This causes the task to go to kernel/userspace boundary where the signal would be handled and the task would be marked as safe in terms of live patching. There are tasks which are not affected by this technique though. The fake signal is not sent to kthreads. They should be handled differently. They can be woken up so they leave the patched set and their TIF_PATCH_PENDING can be cleared thanks to stack checking. For the sake of completeness, if the task is in TASK_RUNNING state but not currently running on some CPU it doesn't get the IPI, but it would eventually handle the signal anyway. Second, if the task runs in the kernel (in TASK_RUNNING state) it gets the IPI, but the signal is not handled on return from the interrupt. It would be handled on return to the userspace in the future when the fake signal is sent again. Stack checking deals with these cases in a better way. If the task was sleeping in a syscall it would be woken by our fake signal, it would check if TIF_SIGPENDING is set (by calling signal_pending() predicate) and return ERESTART* or EINTR. Syscalls with ERESTART* return values are restarted in case of the fake signal (see do_signal()). EINTR is propagated back to the userspace program. This could disturb the program, but... * each process dealing with signals should react accordingly to EINTR return values. * syscalls returning EINTR happen to be quite common situation in the system even if no fake signal is sent. * freezer sends the fake signal and does not deal with EINTR anyhow. Thus EINTR values are returned when the system is resumed. The very safe marking is done in architectures' "entry" on syscall and interrupt/exception exit paths, and in a stack checking functions of livepatch. TIF_PATCH_PENDING is cleared and the next recalc_sigpending() drops TIF_SIGPENDING. In connection with this, also call klp_update_patch_state() before do_signal(), so that recalc_sigpending() in dequeue_signal() can clear TIF_PATCH_PENDING immediately and thus prevent a double call of do_signal(). Note that the fake signal is not sent to stopped/traced tasks. Such task prevents the patching to finish till it continues again (is not traced anymore). Last, sending the fake signal is not automatic. It is done only when admin requests it by writing 1 to signal sysfs attribute in livepatch sysfs directory. Signed-off-by: Miroslav Benes <mbenes@suse.cz> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: linuxppc-dev@lists.ozlabs.org Cc: x86@kernel.org --- Documentation/ABI/testing/sysfs-kernel-livepatch | 9 ++++++ Documentation/livepatch/livepatch.txt | 9 ++++++ arch/powerpc/kernel/signal.c | 6 ++-- arch/x86/entry/common.c | 6 ++-- kernel/livepatch/core.c | 27 ++++++++++++++++ kernel/livepatch/transition.c | 40 ++++++++++++++++++++++++ kernel/livepatch/transition.h | 1 + kernel/signal.c | 4 ++- 8 files changed, 95 insertions(+), 7 deletions(-)