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entry: Add support for TIF_NOTIFY_SIGNAL

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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: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20201026203230.386348-3-axboe@kernel.dk
This commit is contained in:
Jens Axboe 2020-10-26 14:32:28 -06:00 • committed by Thomas Gleixner
parent 5c251e9dc0
commit 12db8b6900
8 changed files with 77 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

11
include/linux/entry-common.h
View file

@ -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()

4
include/linux/entry-kvm.h
View file

@ -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;

11
include/linux/sched/signal.h
View file

@ -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();
}

27
include/linux/tracehook.h
View file

@ -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> */