Commit 12db8b69 authored by Jens Axboe's avatar Jens Axboe Committed by Thomas Gleixner
Browse files

entry: Add support for TIF_NOTIFY_SIGNAL 



Add TIF_NOTIFY_SIGNAL handling in the generic entry 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.

In preparation for only having arch_do_signal() handle syscall restarts if
_TIF_SIGPENDING isn't set, rename it to arch_do_signal_or_restart().  Pass
in a boolean that tells the architecture specific signal handler if it
should attempt to get a signal, or just process a potential syscall
restart.

For !CONFIG_GENERIC_ENTRY archs, add the TIF_NOTIFY_SIGNAL handling to
get_signal(). This is done to minimize the needed architecture changes to
support this feature.

Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20201026203230.386348-3-axboe@kernel.dk
parent 5c251e9d

arch/x86/kernel/signal.c

+2 −2
Original line number Diff line number Diff line
@@ -804,11 +804,11 @@ 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_or_restart(struct pt_regs *regs, bool has_signal)

{

	struct ksignal ksig;



	if (get_signal(&ksig)) {

	if (has_signal && get_signal(&ksig)) {

		/* Whee! Actually deliver the signal.  */

		handle_signal(&ksig, regs);

		return;

include/linux/entry-common.h

+8 −3
Original line number Diff line number Diff line
@@ -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)



/**
@@ -226,12 +230,13 @@ static __always_inline void arch_exit_to_user_mode(void) { } 
#endif



/**

 * arch_do_signal -  Architecture specific signal delivery function

 * arch_do_signal_or_restart -  Architecture specific signal delivery function

 * @regs:	Pointer to currents pt_regs

 * @has_signal:	actual signal to handle

 *

 * Invoked from exit_to_user_mode_loop().

 */

void arch_do_signal(struct pt_regs *regs);

void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal);



/**

 * arch_syscall_exit_tracehook - Wrapper around tracehook_report_syscall_exit()

include/linux/entry-kvm.h

+2 −2
Original line number Diff line number Diff line
@@ -12,7 +12,7 @@ 
#endif



#define XFER_TO_GUEST_MODE_WORK						\

	(_TIF_NEED_RESCHED | _TIF_SIGPENDING |			\

	(_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL |	\

	 _TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK)



struct kvm_vcpu;

include/linux/sched/signal.h

+10 −1
Original line number Diff line number Diff line
@@ -360,6 +360,15 @@ static inline int task_sigpending(struct task_struct *p) 


static inline int signal_pending(struct task_struct *p)

{

#if 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();

}

include/linux/tracehook.h

+27 −0
Original line number Diff line number Diff line
@@ -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(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(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> */

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