Re: pselect/etc semantics (Was: [PATCH v2] signal: Adjust error codes according to restore_user_sigmask())

[Deepa Dinamani <deepa.kernel@gmail.com>]

Resending due to inadvertent conversion of prior message to html.

On Wed, May 29, 2019 at 9:12 AM Oleg Nesterov <oleg@redhat.com> wrote:
> Al, Linus, Eric, please help.
>
> The previous discussion was very confusing, we simply can not understand each
> other.
>
> To me everything looks very simple and clear, but perhaps I missed something
> obvious? Please correct me.
>
> I think that the following code is correct
>
>         int interrupted = 0;
>
>         void sigint_handler(int sig)
>         {
>                 interrupted = 1;
>         }
>
>         int main(void)
>         {
>                 sigset_t sigint, empty;
>
>                 sigemptyset(&sigint);
>                 sigaddset(&sigint, SIGINT);
>                 sigprocmask(SIG_BLOCK, &sigint, NULL);
>
>                 signal(SIGINT, sigint_handler);
>
>                 sigemptyset(&empty);    // so pselect() unblocks SIGINT
>
>                 ret = pselect(..., &empty);
>
>                 if (ret >= 0)           // sucess or timeout
>                         assert(!interrupted);
>
>                 if (interrupted)
>                         assert(ret == -EINTR);
>         }
>
> IOW, if pselect(sigmask) temporary unblocks SIGINT according to sigmask, this
> signal should not be delivered if a ready fd was found or timeout. The signal
> handle should only run if ret == -EINTR.
>
> (pselect() can be interrupted by any other signal which has a handler. In this
>  case the handler can be called even if ret >= 0. This is correct, I fail to
>  understand why some people think this is wrong, and in any case we simply can't
>  avoid this).
>
> This was true until 854a6ed56839a ("signal: Add restore_user_sigmask()"),
> now this is broken by the signal_pending() check in restore_user_sigmask().
>
> This patch https://lore.kernel.org/lkml/20190522032144.10995-1-deepa.kernel@gmail.com/
> turns 0 into -EINTR if signal_pending(), but I think we should simply restore
> the old behaviour and simplify the code.
>
> See the compile-tested patch at the end. Of course, the new _xxx() helpers
> should be renamed somehow. fs/aio.c doesn't look right with or without this
> patch, but iiuc this is what it did before 854a6ed56839a.
>
> Let me show the code with the patch applied. I am using epoll_pwait() as an
> example because it looks very simple.
>
>
>         static inline void set_restore_sigmask(void)
>         {
> // WARN_ON(!TIF_SIGPENDING) was removed by this patch
>                 current->restore_sigmask = true;
>         }
>
>         int set_xxx(const sigset_t __user *umask, size_t sigsetsize)
>         {
>                 sigset_t *kmask;
>
>                 if (!umask)
>                         return 0;
>                 if (sigsetsize != sizeof(sigset_t))
>                         return -EINVAL;
>                 if (copy_from_user(kmask, umask, sizeof(sigset_t)))
>                         return -EFAULT;
>
> // we can safely modify ->saved_sigmask/restore_sigmask, they has no meaning
> // until the syscall returns.
>                 set_restore_sigmask();
>                 current->saved_sigmask = current->blocked;
>                 set_current_blocked(kmask);
>
>                 return 0;
>         }
>
>
>         void update_xxx(bool interrupted)
>         {
> // the main reason for this helper is WARN_ON(!TIF_SIGPENDING) which was "moved"
> // from set_restore_sigmask() above.
>                 if (interrupted)
>                         WARN_ON(!test_thread_flag(TIF_SIGPENDING));
>                 else
>                         restore_saved_sigmask();
>         }
>
>         SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
>                         int, maxevents, int, timeout, const sigset_t __user *, sigmask,
>                         size_t, sigsetsize)
>         {
>                 int error;
>
>                 error = set_xxx(sigmask, sigsetsize);
>                 if (error)
>                         return error;
>
>                 error = do_epoll_wait(epfd, events, maxevents, timeout);
>                 update_xxx(error == -EINTR);
>
>                 return error;
>         }
>
> Oleg.
> ---
>
>  fs/aio.c                     | 40 ++++++++++++++---------
>  fs/eventpoll.c               | 12 +++----
>  fs/io_uring.c                | 12 +++----
>  fs/select.c                  | 40 +++++++----------------
>  include/linux/compat.h       |  4 +--
>  include/linux/sched/signal.h |  2 --
>  include/linux/signal.h       |  6 ++--
>  kernel/signal.c              | 77 ++++++++++++++++----------------------------
>  8 files changed, 74 insertions(+), 119 deletions(-)
>
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 3490d1f..8315bd2 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -2093,8 +2093,8 @@ SYSCALL_DEFINE6(io_pgetevents,
>                 const struct __aio_sigset __user *, usig)
>  {
>         struct __aio_sigset     ksig = { NULL, };
> -       sigset_t                ksigmask, sigsaved;
>         struct timespec64       ts;
> +       bool interrupted;
>         int ret;
>
>         if (timeout && unlikely(get_timespec64(&ts, timeout)))
> @@ -2103,13 +2103,15 @@ SYSCALL_DEFINE6(io_pgetevents,

I already admitted I was wrong about this. And the behavior you point out
is consistent with man page. I'm not sure why we are not understanding that
I'm agreeing with you:
https://lore.kernel.org/lkml/CABeXuvouBzZuNarmNcd9JgZgvonL1N_p21gat=O_x0-1hMx=6A@mail.gmail.com/

This was true until 854a6ed56839a("signal: Add restore_user_sigmask()"),

now this is broken by the signal_pending() check in restore_user_sigmask().

This patch is wrong because I did not know about the above behavior before.
I also admitted to this. And proposed another way to revert the patch.

This patch
https://lore.kernel.org/lkml/20190522032144.10995-1-deepa.kernel@gmail.com/
turns 0 into -EINTR if signal_pending(), but I think we should simply
restore the old behaviour and simplify the code.


I agree that the patch that turns 0 to -EINTR should not be applied.
It was my misunderstanding.

The part I'm not sure is that I cannot find anything that is wrong with
854a6ed56839a("signal: Add restore_user_sigmask()") that was not already before.
But, that is ok, we can do the revert and I will investigate with the
test application if I can find something.

-Deepa
>         if (usig && copy_from_user(&ksig, usig, sizeof(ksig)))
>                 return -EFAULT;
>
> -       ret = set_user_sigmask(ksig.sigmask, &ksigmask, &sigsaved, ksig.sigsetsize);
> +       ret = set_xxx(ksig.sigmask, ksig.sigsetsize);
>         if (ret)
>                 return ret;
>
>         ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &ts : NULL);
> -       restore_user_sigmask(ksig.sigmask, &sigsaved);
> -       if (signal_pending(current) && !ret)
> +
> +       interrupted = signal_pending(current);
> +       update_xxx(interrupted);
> +       if (interrupted && !ret)
>                 ret = -ERESTARTNOHAND;
>
>         return ret;
> @@ -2126,8 +2128,8 @@ SYSCALL_DEFINE6(io_pgetevents_time32,
>                 const struct __aio_sigset __user *, usig)
>  {
>         struct __aio_sigset     ksig = { NULL, };
> -       sigset_t                ksigmask, sigsaved;
>         struct timespec64       ts;
> +       bool interrupted;
>         int ret;
>
>         if (timeout && unlikely(get_old_timespec32(&ts, timeout)))
> @@ -2137,13 +2139,15 @@ SYSCALL_DEFINE6(io_pgetevents_time32,
>                 return -EFAULT;
>
>
> -       ret = set_user_sigmask(ksig.sigmask, &ksigmask, &sigsaved, ksig.sigsetsize);
> +       ret = set_xxx(ksig.sigmask, ksig.sigsetsize);
>         if (ret)
>                 return ret;
>
>         ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &ts : NULL);
> -       restore_user_sigmask(ksig.sigmask, &sigsaved);
> -       if (signal_pending(current) && !ret)
> +
> +       interrupted = signal_pending(current);
> +       update_xxx(interrupted);
> +       if (interrupted && !ret)
>                 ret = -ERESTARTNOHAND;
>
>         return ret;
> @@ -2191,8 +2195,8 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents,
>                 const struct __compat_aio_sigset __user *, usig)
>  {
>         struct __compat_aio_sigset ksig = { NULL, };
> -       sigset_t ksigmask, sigsaved;
>         struct timespec64 t;
> +       bool interrupted;
>         int ret;
>
>         if (timeout && get_old_timespec32(&t, timeout))
> @@ -2201,13 +2205,15 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents,
>         if (usig && copy_from_user(&ksig, usig, sizeof(ksig)))
>                 return -EFAULT;
>
> -       ret = set_compat_user_sigmask(ksig.sigmask, &ksigmask, &sigsaved, ksig.sigsetsize);
> +       ret = set_compat_xxx(ksig.sigmask, ksig.sigsetsize);
>         if (ret)
>                 return ret;
>
>         ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &t : NULL);
> -       restore_user_sigmask(ksig.sigmask, &sigsaved);
> -       if (signal_pending(current) && !ret)
> +
> +       interrupted = signal_pending(current);
> +       update_xxx(interrupted);
> +       if (interrupted && !ret)
>                 ret = -ERESTARTNOHAND;
>
>         return ret;
> @@ -2224,8 +2230,8 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents_time64,
>                 const struct __compat_aio_sigset __user *, usig)
>  {
>         struct __compat_aio_sigset ksig = { NULL, };
> -       sigset_t ksigmask, sigsaved;
>         struct timespec64 t;
> +       bool interrupted;
>         int ret;
>
>         if (timeout && get_timespec64(&t, timeout))
> @@ -2234,13 +2240,15 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents_time64,
>         if (usig && copy_from_user(&ksig, usig, sizeof(ksig)))
>                 return -EFAULT;
>
> -       ret = set_compat_user_sigmask(ksig.sigmask, &ksigmask, &sigsaved, ksig.sigsetsize);
> +       ret = set_compat_xxx(ksig.sigmask, ksig.sigsetsize);
>         if (ret)
>                 return ret;
>
>         ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &t : NULL);
> -       restore_user_sigmask(ksig.sigmask, &sigsaved);
> -       if (signal_pending(current) && !ret)
> +
> +       interrupted = signal_pending(current);
> +       update_xxx(interrupted);
> +       if (interrupted && !ret)
>                 ret = -ERESTARTNOHAND;
>
>         return ret;
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 4a0e98d..0b1a337 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -2318,19 +2318,17 @@ SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
>                 size_t, sigsetsize)
>  {
>         int error;
> -       sigset_t ksigmask, sigsaved;
>
>         /*
>          * If the caller wants a certain signal mask to be set during the wait,
>          * we apply it here.
>          */
> -       error = set_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
> +       error = set_xxx(sigmask, sigsetsize);
>         if (error)
>                 return error;
>
>         error = do_epoll_wait(epfd, events, maxevents, timeout);
> -
> -       restore_user_sigmask(sigmask, &sigsaved);
> +       update_xxx(error == -EINTR);
>
>         return error;
>  }
> @@ -2343,19 +2341,17 @@ COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
>                         compat_size_t, sigsetsize)
>  {
>         long err;
> -       sigset_t ksigmask, sigsaved;
>
>         /*
>          * If the caller wants a certain signal mask to be set during the wait,
>          * we apply it here.
>          */
> -       err = set_compat_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
> +       err = set_compat_xxx(sigmask, sigsetsize);
>         if (err)
>                 return err;
>
>         err = do_epoll_wait(epfd, events, maxevents, timeout);
> -
> -       restore_user_sigmask(sigmask, &sigsaved);
> +       update_xxx(err == -EINTR);
>
>         return err;
>  }
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 310f8d1..b5b99e2 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2180,7 +2180,6 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
>                           const sigset_t __user *sig, size_t sigsz)
>  {
>         struct io_cq_ring *ring = ctx->cq_ring;
> -       sigset_t ksigmask, sigsaved;
>         int ret;
>
>         if (io_cqring_events(ring) >= min_events)
> @@ -2189,24 +2188,21 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
>         if (sig) {
>  #ifdef CONFIG_COMPAT
>                 if (in_compat_syscall())
> -                       ret = set_compat_user_sigmask((const compat_sigset_t __user *)sig,
> -                                                     &ksigmask, &sigsaved, sigsz);
> +                       ret = set_compat_xxx((const compat_sigset_t __user *)sig,
> +                                                     sigsz);
>                 else
>  #endif
> -                       ret = set_user_sigmask(sig, &ksigmask,
> -                                              &sigsaved, sigsz);
> +                       ret = set_xxx(sig, sigsz);
>
>                 if (ret)
>                         return ret;
>         }
>
>         ret = wait_event_interruptible(ctx->wait, io_cqring_events(ring) >= min_events);
> +       update_xxx(ret == -ERESTARTSYS);
>         if (ret == -ERESTARTSYS)
>                 ret = -EINTR;
>
> -       if (sig)
> -               restore_user_sigmask(sig, &sigsaved);
> -
>         return READ_ONCE(ring->r.head) == READ_ONCE(ring->r.tail) ? ret : 0;
>  }
>
> diff --git a/fs/select.c b/fs/select.c
> index 6cbc9ff..7eab132 100644
> --- a/fs/select.c
> +++ b/fs/select.c
> @@ -730,7 +730,6 @@ static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp,
>                        const sigset_t __user *sigmask, size_t sigsetsize,
>                        enum poll_time_type type)
>  {
> -       sigset_t ksigmask, sigsaved;
>         struct timespec64 ts, end_time, *to = NULL;
>         int ret;
>
> @@ -753,15 +752,14 @@ static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp,
>                         return -EINVAL;
>         }
>
> -       ret = set_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
> +       ret = set_xxx(sigmask, sigsetsize);
>         if (ret)
>                 return ret;
>
>         ret = core_sys_select(n, inp, outp, exp, to);
> +       update_xxx(ret == -ERESTARTNOHAND);
>         ret = poll_select_copy_remaining(&end_time, tsp, type, ret);
>
> -       restore_user_sigmask(sigmask, &sigsaved);
> -
>         return ret;
>  }
>
> @@ -1087,7 +1085,6 @@ SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds, unsigned int, nfds,
>                 struct __kernel_timespec __user *, tsp, const sigset_t __user *, sigmask,
>                 size_t, sigsetsize)
>  {
> -       sigset_t ksigmask, sigsaved;
>         struct timespec64 ts, end_time, *to = NULL;
>         int ret;
>
> @@ -1100,18 +1097,16 @@ SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds, unsigned int, nfds,
>                         return -EINVAL;
>         }
>
> -       ret = set_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
> +       ret = set_xxx(sigmask, sigsetsize);
>         if (ret)
>                 return ret;
>
>         ret = do_sys_poll(ufds, nfds, to);
>
> -       restore_user_sigmask(sigmask, &sigsaved);
> -
> +       update_xxx(ret == -EINTR);
>         /* We can restart this syscall, usually */
>         if (ret == -EINTR)
>                 ret = -ERESTARTNOHAND;
> -
>         ret = poll_select_copy_remaining(&end_time, tsp, PT_TIMESPEC, ret);
>
>         return ret;
> @@ -1123,7 +1118,6 @@ SYSCALL_DEFINE5(ppoll_time32, struct pollfd __user *, ufds, unsigned int, nfds,
>                 struct old_timespec32 __user *, tsp, const sigset_t __user *, sigmask,
>                 size_t, sigsetsize)
>  {
> -       sigset_t ksigmask, sigsaved;
>         struct timespec64 ts, end_time, *to = NULL;
>         int ret;
>
> @@ -1136,18 +1130,16 @@ SYSCALL_DEFINE5(ppoll_time32, struct pollfd __user *, ufds, unsigned int, nfds,
>                         return -EINVAL;
>         }
>
> -       ret = set_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
> +       ret = set_xxx(sigmask, sigsetsize);
>         if (ret)
>                 return ret;
>
>         ret = do_sys_poll(ufds, nfds, to);
>
> -       restore_user_sigmask(sigmask, &sigsaved);
> -
> +       update_xxx(ret == -EINTR);
>         /* We can restart this syscall, usually */
>         if (ret == -EINTR)
>                 ret = -ERESTARTNOHAND;
> -
>         ret = poll_select_copy_remaining(&end_time, tsp, PT_OLD_TIMESPEC, ret);
>
>         return ret;
> @@ -1322,7 +1314,6 @@ static long do_compat_pselect(int n, compat_ulong_t __user *inp,
>         void __user *tsp, compat_sigset_t __user *sigmask,
>         compat_size_t sigsetsize, enum poll_time_type type)
>  {
> -       sigset_t ksigmask, sigsaved;
>         struct timespec64 ts, end_time, *to = NULL;
>         int ret;
>
> @@ -1345,15 +1336,14 @@ static long do_compat_pselect(int n, compat_ulong_t __user *inp,
>                         return -EINVAL;
>         }
>
> -       ret = set_compat_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
> +       ret = set_compat_xxx(sigmask, sigsetsize);
>         if (ret)
>                 return ret;
>
>         ret = compat_core_sys_select(n, inp, outp, exp, to);
> +       update_xxx(ret == -ERESTARTNOHAND);
>         ret = poll_select_copy_remaining(&end_time, tsp, type, ret);
>
> -       restore_user_sigmask(sigmask, &sigsaved);
> -
>         return ret;
>  }
>
> @@ -1406,7 +1396,6 @@ COMPAT_SYSCALL_DEFINE5(ppoll_time32, struct pollfd __user *, ufds,
>         unsigned int,  nfds, struct old_timespec32 __user *, tsp,
>         const compat_sigset_t __user *, sigmask, compat_size_t, sigsetsize)
>  {
> -       sigset_t ksigmask, sigsaved;
>         struct timespec64 ts, end_time, *to = NULL;
>         int ret;
>
> @@ -1419,18 +1408,16 @@ COMPAT_SYSCALL_DEFINE5(ppoll_time32, struct pollfd __user *, ufds,
>                         return -EINVAL;
>         }
>
> -       ret = set_compat_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
> +       ret = set_compat_xxx(sigmask, sigsetsize);
>         if (ret)
>                 return ret;
>
>         ret = do_sys_poll(ufds, nfds, to);
>
> -       restore_user_sigmask(sigmask, &sigsaved);
> -
> +       update_xxx(ret == -EINTR);
>         /* We can restart this syscall, usually */
>         if (ret == -EINTR)
>                 ret = -ERESTARTNOHAND;
> -
>         ret = poll_select_copy_remaining(&end_time, tsp, PT_OLD_TIMESPEC, ret);
>
>         return ret;
> @@ -1442,7 +1429,6 @@ COMPAT_SYSCALL_DEFINE5(ppoll_time64, struct pollfd __user *, ufds,
>         unsigned int,  nfds, struct __kernel_timespec __user *, tsp,
>         const compat_sigset_t __user *, sigmask, compat_size_t, sigsetsize)
>  {
> -       sigset_t ksigmask, sigsaved;
>         struct timespec64 ts, end_time, *to = NULL;
>         int ret;
>
> @@ -1455,18 +1441,16 @@ COMPAT_SYSCALL_DEFINE5(ppoll_time64, struct pollfd __user *, ufds,
>                         return -EINVAL;
>         }
>
> -       ret = set_compat_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
> +       ret = set_compat_xxx(sigmask, sigsetsize);
>         if (ret)
>                 return ret;
>
>         ret = do_sys_poll(ufds, nfds, to);
>
> -       restore_user_sigmask(sigmask, &sigsaved);
> -
> +       update_xxx(ret == -EINTR);
>         /* We can restart this syscall, usually */
>         if (ret == -EINTR)
>                 ret = -ERESTARTNOHAND;
> -
>         ret = poll_select_copy_remaining(&end_time, tsp, PT_TIMESPEC, ret);
>
>         return ret;
> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index ebddcb6..b20b001 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -138,9 +138,7 @@ typedef struct {
>         compat_sigset_word      sig[_COMPAT_NSIG_WORDS];
>  } compat_sigset_t;
>
> -int set_compat_user_sigmask(const compat_sigset_t __user *usigmask,
> -                           sigset_t *set, sigset_t *oldset,
> -                           size_t sigsetsize);
> +int set_compat_xxx(const compat_sigset_t __user *umask, size_t sigsetsize);
>
>  struct compat_sigaction {
>  #ifndef __ARCH_HAS_IRIX_SIGACTION
> diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
> index 38a0f07..8b5b537 100644
> --- a/include/linux/sched/signal.h
> +++ b/include/linux/sched/signal.h
> @@ -417,7 +417,6 @@ void task_join_group_stop(struct task_struct *task);
>  static inline void set_restore_sigmask(void)
>  {
>         set_thread_flag(TIF_RESTORE_SIGMASK);
> -       WARN_ON(!test_thread_flag(TIF_SIGPENDING));
>  }
>
>  static inline void clear_tsk_restore_sigmask(struct task_struct *task)
> @@ -448,7 +447,6 @@ static inline bool test_and_clear_restore_sigmask(void)
>  static inline void set_restore_sigmask(void)
>  {
>         current->restore_sigmask = true;
> -       WARN_ON(!test_thread_flag(TIF_SIGPENDING));
>  }
>  static inline void clear_tsk_restore_sigmask(struct task_struct *task)
>  {
> diff --git a/include/linux/signal.h b/include/linux/signal.h
> index 9702016..65f84ac 100644
> --- a/include/linux/signal.h
> +++ b/include/linux/signal.h
> @@ -273,10 +273,8 @@ extern int group_send_sig_info(int sig, struct kernel_siginfo *info,
>                                struct task_struct *p, enum pid_type type);
>  extern int __group_send_sig_info(int, struct kernel_siginfo *, struct task_struct *);
>  extern int sigprocmask(int, sigset_t *, sigset_t *);
> -extern int set_user_sigmask(const sigset_t __user *usigmask, sigset_t *set,
> -       sigset_t *oldset, size_t sigsetsize);
> -extern void restore_user_sigmask(const void __user *usigmask,
> -                                sigset_t *sigsaved);
> +extern int set_xxx(const sigset_t __user *umask, size_t sigsetsize);
> +extern void update_xxx(bool interupted);
>  extern void set_current_blocked(sigset_t *);
>  extern void __set_current_blocked(const sigset_t *);
>  extern int show_unhandled_signals;
> diff --git a/kernel/signal.c b/kernel/signal.c
> index d7b9d14..0a1ec68 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2861,79 +2861,56 @@ EXPORT_SYMBOL(sigprocmask);
>   *
>   * This is useful for syscalls such as ppoll, pselect, io_pgetevents and
>   * epoll_pwait where a new sigmask is passed from userland for the syscalls.
> + *
> + * Note that it does set_restore_sigmask() in advance, so it must be always
> + * paired with update_xxx() before return from syscall.
>   */
> -int set_user_sigmask(const sigset_t __user *usigmask, sigset_t *set,
> -                    sigset_t *oldset, size_t sigsetsize)
> +int set_xxx(const sigset_t __user *umask, size_t sigsetsize)
>  {
> -       if (!usigmask)
> -               return 0;
> +       sigset_t *kmask;
>
> +       if (!umask)
> +               return 0;
>         if (sigsetsize != sizeof(sigset_t))
>                 return -EINVAL;
> -       if (copy_from_user(set, usigmask, sizeof(sigset_t)))
> +       if (copy_from_user(kmask, umask, sizeof(sigset_t)))
>                 return -EFAULT;
>
> -       *oldset = current->blocked;
> -       set_current_blocked(set);
> +       set_restore_sigmask();
> +       current->saved_sigmask = current->blocked;
> +       set_current_blocked(kmask);
>
>         return 0;
>  }
> -EXPORT_SYMBOL(set_user_sigmask);
> +
> +void update_xxx(bool interrupted)
> +{
> +       if (interrupted)
> +               WARN_ON(!test_thread_flag(TIF_SIGPENDING));
> +       else
> +               restore_saved_sigmask();
> +}
>
>  #ifdef CONFIG_COMPAT
> -int set_compat_user_sigmask(const compat_sigset_t __user *usigmask,
> -                           sigset_t *set, sigset_t *oldset,
> -                           size_t sigsetsize)
> +int set_compat_xxx(const compat_sigset_t __user *umask, size_t sigsetsize)
>  {
> -       if (!usigmask)
> -               return 0;
> +       sigset_t *kmask;
>
> +       if (!umask)
> +               return 0;
>         if (sigsetsize != sizeof(compat_sigset_t))
>                 return -EINVAL;
> -       if (get_compat_sigset(set, usigmask))
> +       if (get_compat_sigset(kmask, umask))
>                 return -EFAULT;
>
> -       *oldset = current->blocked;
> -       set_current_blocked(set);
> +       set_restore_sigmask();
> +       current->saved_sigmask = current->blocked;
> +       set_current_blocked(kmask);
>
>         return 0;
>  }
> -EXPORT_SYMBOL(set_compat_user_sigmask);
>  #endif
>
> -/*
> - * restore_user_sigmask:
> - * usigmask: sigmask passed in from userland.
> - * sigsaved: saved sigmask when the syscall started and changed the sigmask to
> - *           usigmask.
> - *
> - * This is useful for syscalls such as ppoll, pselect, io_pgetevents and
> - * epoll_pwait where a new sigmask is passed in from userland for the syscalls.
> - */
> -void restore_user_sigmask(const void __user *usigmask, sigset_t *sigsaved)
> -{
> -
> -       if (!usigmask)
> -               return;
> -       /*
> -        * When signals are pending, do not restore them here.
> -        * Restoring sigmask here can lead to delivering signals that the above
> -        * syscalls are intended to block because of the sigmask passed in.
> -        */
> -       if (signal_pending(current)) {
> -               current->saved_sigmask = *sigsaved;
> -               set_restore_sigmask();
> -               return;
> -       }
> -
> -       /*
> -        * This is needed because the fast syscall return path does not restore
> -        * saved_sigmask when signals are not pending.
> -        */
> -       set_current_blocked(sigsaved);
> -}
> -EXPORT_SYMBOL(restore_user_sigmask);
> -
>  /**
>   *  sys_rt_sigprocmask - change the list of currently blocked signals
>   *  @how: whether to add, remove, or set signals
>