ARM: 5677/1: ARM support for TIF_RESTORE_SIGMASK/pselect6/ppoll/epoll_pwait

This patch adds support for TIF_RESTORE_SIGMASK to ARM's
signal handling, which allows to hook up the pselect6, ppoll,
and epoll_pwait syscalls on ARM.

Tested here with eabi userspace and a test program with a
deliberate race between a child's exit and the parent's
sigprocmask/select sequence. Using sys_pselect6() instead
of sigprocmask/select reliably prevents the race.

The other arch's support for TIF_RESTORE_SIGMASK has evolved
over time:

In 2.6.16:
- add TIF_RESTORE_SIGMASK which parallels TIF_SIGPENDING
- test both when checking for pending signal [changed later]
- reimplement sys_sigsuspend() to use current->saved_sigmask,
  TIF_RESTORE_SIGMASK [changed later], and -ERESTARTNOHAND;
  ditto for sys_rt_sigsuspend(), but drop private code and
  use common code via __ARCH_WANT_SYS_RT_SIGSUSPEND;
- there are now no "extra" calls to do_signal() so its oldset
  parameter is always &current->blocked so need not be passed,
  also its return value is changed to void
- change handle_signal() to return 0/-errno
- change do_signal() to honor TIF_RESTORE_SIGMASK:
  + get oldset from current->saved_sigmask if TIF_RESTORE_SIGMASK
    is set
  + if handle_signal() was successful then clear TIF_RESTORE_SIGMASK
  + if no signal was delivered and TIF_RESTORE_SIGMASK is set then
    clear it and restore the sigmask
- hook up sys_pselect6() and sys_ppoll()

In 2.6.19:
- hook up sys_epoll_pwait()

In 2.6.26:
- allow archs to override how TIF_RESTORE_SIGMASK is implemented;
  default set_restore_sigmask() sets both TIF_RESTORE_SIGMASK and
  TIF_SIGPENDING; archs need now just test TIF_SIGPENDING again
  when checking for pending signal work; some archs now implement
  TIF_RESTORE_SIGMASK as a secondary/non-atomic thread flag bit
- call set_restore_sigmask() in sys_sigsuspend() instead of setting
  TIF_RESTORE_SIGMASK

In 2.6.29-rc:
- kill sys_pselect7() which no arch wanted

So for 2.6.31-rc6/ARM this patch does the following:
- Add TIF_RESTORE_SIGMASK. Use the generic set_restore_sigmask()
  which sets both TIF_SIGPENDING and TIF_RESTORE_SIGMASK, so
  TIF_RESTORE_SIGMASK need not claim one of the scarce low thread
  flags, and existing TIF_SIGPENDING and _TIF_WORK_MASK tests need
  not be extended for TIF_RESTORE_SIGMASK.
- sys_sigsuspend() is reimplemented to use current->saved_sigmask
  and set_restore_sigmask(), making it identical to most other archs
- The private code for sys_rt_sigsuspend() is removed, instead
  generic code supplies it via __ARCH_WANT_SYS_RT_SIGSUSPEND.
- sys_sigsuspend() and sys_rt_sigsuspend() no longer need a pt_regs
  parameter, so their assembly code wrappers are removed.
- handle_signal() is changed to return 0 on success or -errno.
- The oldset parameter to do_signal() is now redundant and removed,
  and the return value is now also redundant and changed to void.
- do_signal() is changed to honor TIF_RESTORE_SIGMASK:
  + get oldset from current->saved_sigmask if TIF_RESTORE_SIGMASK
    is set
  + if handle_signal() was successful then clear TIF_RESTORE_SIGMASK
  + if no signal was delivered and TIF_RESTORE_SIGMASK is set then
    clear it and restore the sigmask
- Hook up sys_pselect6, sys_ppoll, and sys_epoll_pwait.

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 37 insertions, 49 deletions

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 93bb4247b7ed..e27ee1f701d5 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -47,57 +47,22 @@ const unsigned long sigreturn_codes[7] = {
         MOV_R7_NR_RT_SIGRETURN, SWI_SYS_RT_SIGRETURN, SWI_THUMB_RT_SIGRETURN,
 };
 
-static int do_signal(sigset_t *oldset, struct pt_regs * regs, int syscall);
-
 /*
  * atomically swap in the new signal mask, and wait for a signal.
  */
-asmlinkage int sys_sigsuspend(int restart, unsigned long oldmask, old_sigset_t mask, struct pt_regs *regs)
+asmlinkage int sys_sigsuspend(int restart, unsigned long oldmask, old_sigset_t mask)
 {
-        sigset_t saveset;
-
         mask &= _BLOCKABLE;
         spin_lock_irq(&current->sighand->siglock);
-        saveset = current->blocked;
+        current->saved_sigmask = current->blocked;
         siginitset(&current->blocked, mask);
         recalc_sigpending();
         spin_unlock_irq(&current->sighand->siglock);
-        regs->ARM_r0 = -EINTR;
-
-        while (1) {
-                current->state = TASK_INTERRUPTIBLE;
-                schedule();
-                if (do_signal(&saveset, regs, 0))
-                        return regs->ARM_r0;
-        }
-}
-
-asmlinkage int
-sys_rt_sigsuspend(sigset_t __user *unewset, size_t sigsetsize, struct pt_regs *regs)
-{
-        sigset_t saveset, newset;
-
-        /* XXX: Don't preclude handling different sized sigset_t's. */
-        if (sigsetsize != sizeof(sigset_t))
-                return -EINVAL;
-
-        if (copy_from_user(&newset, unewset, sizeof(newset)))
-                return -EFAULT;
-        sigdelsetmask(&newset, ~_BLOCKABLE);
-
-        spin_lock_irq(&current->sighand->siglock);
-        saveset = current->blocked;
-        current->blocked = newset;
-        recalc_sigpending();
-        spin_unlock_irq(&current->sighand->siglock);
-        regs->ARM_r0 = -EINTR;
 
-        while (1) {
-                current->state = TASK_INTERRUPTIBLE;
-                schedule();
-                if (do_signal(&saveset, regs, 0))
-                        return regs->ARM_r0;
-        }
+        current->state = TASK_INTERRUPTIBLE;
+        schedule();
+        set_restore_sigmask();
+        return -ERESTARTNOHAND;
 }
 
 asmlinkage int 
@@ -545,7 +510,7 @@ static inline void setup_syscall_restart(struct pt_regs *regs)
 /*
  * OK, we're invoking a handler
  */     
-static void
+static int
 handle_signal(unsigned long sig, struct k_sigaction *ka,
               siginfo_t *info, sigset_t *oldset,
               struct pt_regs * regs, int syscall)
@@ -596,7 +561,7 @@ handle_signal(unsigned long sig, struct k_sigaction *ka,
 
         if (ret != 0) {
                 force_sigsegv(sig, tsk);
-                return;
+                return ret;
         }
 
         /*
@@ -610,6 +575,7 @@ handle_signal(unsigned long sig, struct k_sigaction *ka,
         recalc_sigpending();
         spin_unlock_irq(&tsk->sighand->siglock);
 
+        return 0;
 }
 
 /*
@@ -621,7 +587,7 @@ handle_signal(unsigned long sig, struct k_sigaction *ka,
  * the kernel can handle, and then we build all the user-level signal handling
  * stack-frames in one go after that.
  */
-static int do_signal(sigset_t *oldset, struct pt_regs *regs, int syscall)
+static void do_signal(struct pt_regs *regs, int syscall)
 {
         struct k_sigaction ka;
         siginfo_t info;
@@ -634,7 +600,7 @@ static int do_signal(sigset_t *oldset, struct pt_regs *regs, int syscall)
          * if so.
          */
         if (!user_mode(regs))
-                return 0;
+                return;
 
         if (try_to_freeze())
                 goto no_signal;
@@ -643,9 +609,24 @@ static int do_signal(sigset_t *oldset, struct pt_regs *regs, int syscall)
 
         signr = get_signal_to_deliver(&info, &ka, regs, NULL);
         if (signr > 0) {
-                handle_signal(signr, &ka, &info, oldset, regs, syscall);
+                sigset_t *oldset;
+
+                if (test_thread_flag(TIF_RESTORE_SIGMASK))
+                        oldset = &current->saved_sigmask;
+                else
+                        oldset = &current->blocked;
+                if (handle_signal(signr, &ka, &info, oldset, regs, syscall) == 0) {
+                        /*
+                         * A signal was successfully delivered; the saved
+                         * sigmask will have been stored in the signal frame,
+                         * and will be restored by sigreturn, so we can simply
+                         * clear the TIF_RESTORE_SIGMASK flag.
+                         */
+                        if (test_thread_flag(TIF_RESTORE_SIGMASK))
+                                clear_thread_flag(TIF_RESTORE_SIGMASK);
+                }
                 single_step_set(current);
-                return 1;
+                return;
         }
 
  no_signal:
@@ -697,14 +678,21 @@ static int do_signal(sigset_t *oldset, struct pt_regs *regs, int syscall)
                     regs->ARM_r0 == -ERESTARTNOINTR) {
                         setup_syscall_restart(regs);
                 }
+
+                /* If there's no signal to deliver, we just put the saved sigmask
+                 * back.
+                 */
+                if (test_thread_flag(TIF_RESTORE_SIGMASK)) {
+                        clear_thread_flag(TIF_RESTORE_SIGMASK);
+                        sigprocmask(SIG_SETMASK, &current->saved_sigmask, NULL);
+                }
         }
         single_step_set(current);
-        return 0;
 }
 
 asmlinkage void
 do_notify_resume(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 {
         if (thread_flags & _TIF_SIGPENDING)
-                do_signal(&current->blocked, regs, syscall);
+                do_signal(regs, syscall);
 }