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+From: Mikael Pettersson <mikpe@it.uu.se>
+Newsgroups: gmane.linux.ports.arm.kernel
+Subject: [PATCH][v3] ARM support for
+ TIF_RESTORE_SIGMASK/pselect6/ppoll/epoll_pwait
+Date: Sat, 15 Aug 2009 13:09:28 +0200 (MEST)
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+Xref: news.gmane.org gmane.linux.ports.arm.kernel:64340
+Archived-At: <http://permalink.gmane.org/gmane.linux.ports.arm.kernel/64340>
+
+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 [bad, 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 ¤t->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 so it's 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
+---
+Changes from previous versions:
+
+v2 (only posted as incremental diff against v1):
+- moved sigmask restoration in no-signal-delivered case into
+ "if (syscall)" block for extra protection against exception
+ path also invoking do_signal()
+v3 (this version):
+- moved oldset initialisation into "if (signr > 0)" block,
+ as requested by Russell
+
+ arch/arm/include/asm/thread_info.h | 2
+ arch/arm/include/asm/unistd.h | 7 +--
+ arch/arm/kernel/calls.S | 10 ++--
+ arch/arm/kernel/entry-common.S | 10 ----
+ arch/arm/kernel/signal.c | 86 +++++++++++++++----------------------
+ 5 files changed, 48 insertions(+), 67 deletions(-)
+
+diff -rupN linux-2.6.31-rc6/arch/arm/include/asm/thread_info.h linux-2.6.31-rc6.arm-restore-sigmask-v3/arch/arm/include/asm/thread_info.h
+--- linux-2.6.31-rc6/arch/arm/include/asm/thread_info.h 2009-08-14 11:11:10.000000000 +0200
++++ linux-2.6.31-rc6.arm-restore-sigmask-v3/arch/arm/include/asm/thread_info.h 2009-08-14 11:26:44.000000000 +0200
+@@ -140,6 +140,7 @@ extern void vfp_sync_state(struct thread
+ #define TIF_USING_IWMMXT 17
+ #define TIF_MEMDIE 18
+ #define TIF_FREEZE 19
++#define TIF_RESTORE_SIGMASK 20
+
+ #define _TIF_SIGPENDING (1 << TIF_SIGPENDING)
+ #define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
+@@ -147,6 +148,7 @@ extern void vfp_sync_state(struct thread
+ #define _TIF_POLLING_NRFLAG (1 << TIF_POLLING_NRFLAG)
+ #define _TIF_USING_IWMMXT (1 << TIF_USING_IWMMXT)
+ #define _TIF_FREEZE (1 << TIF_FREEZE)
++#define _TIF_RESTORE_SIGMASK (1 << TIF_RESTORE_SIGMASK)
+
+ /*
+ * Change these and you break ASM code in entry-common.S
+diff -rupN linux-2.6.31-rc6/arch/arm/include/asm/unistd.h linux-2.6.31-rc6.arm-restore-sigmask-v3/arch/arm/include/asm/unistd.h
+--- linux-2.6.31-rc6/arch/arm/include/asm/unistd.h 2009-08-14 11:11:10.000000000 +0200
++++ linux-2.6.31-rc6.arm-restore-sigmask-v3/arch/arm/include/asm/unistd.h 2009-08-14 11:26:44.000000000 +0200
+@@ -360,8 +360,8 @@
+ #define __NR_readlinkat (__NR_SYSCALL_BASE+332)
+ #define __NR_fchmodat (__NR_SYSCALL_BASE+333)
+ #define __NR_faccessat (__NR_SYSCALL_BASE+334)
+- /* 335 for pselect6 */
+- /* 336 for ppoll */
++#define __NR_pselect6 (__NR_SYSCALL_BASE+335)
++#define __NR_ppoll (__NR_SYSCALL_BASE+336)
+ #define __NR_unshare (__NR_SYSCALL_BASE+337)
+ #define __NR_set_robust_list (__NR_SYSCALL_BASE+338)
+ #define __NR_get_robust_list (__NR_SYSCALL_BASE+339)
+@@ -372,7 +372,7 @@
+ #define __NR_vmsplice (__NR_SYSCALL_BASE+343)
+ #define __NR_move_pages (__NR_SYSCALL_BASE+344)
+ #define __NR_getcpu (__NR_SYSCALL_BASE+345)
+- /* 346 for epoll_pwait */
++#define __NR_epoll_pwait (__NR_SYSCALL_BASE+346)
+ #define __NR_kexec_load (__NR_SYSCALL_BASE+347)
+ #define __NR_utimensat (__NR_SYSCALL_BASE+348)
+ #define __NR_signalfd (__NR_SYSCALL_BASE+349)
+@@ -432,6 +432,7 @@
+ #define __ARCH_WANT_SYS_SIGPENDING
+ #define __ARCH_WANT_SYS_SIGPROCMASK
+ #define __ARCH_WANT_SYS_RT_SIGACTION
++#define __ARCH_WANT_SYS_RT_SIGSUSPEND
+
+ #if !defined(CONFIG_AEABI) || defined(CONFIG_OABI_COMPAT)
+ #define __ARCH_WANT_SYS_TIME
+diff -rupN linux-2.6.31-rc6/arch/arm/kernel/calls.S linux-2.6.31-rc6.arm-restore-sigmask-v3/arch/arm/kernel/calls.S
+--- linux-2.6.31-rc6/arch/arm/kernel/calls.S 2009-08-14 11:11:10.000000000 +0200
++++ linux-2.6.31-rc6.arm-restore-sigmask-v3/arch/arm/kernel/calls.S 2009-08-14 11:26:44.000000000 +0200
+@@ -81,7 +81,7 @@
+ CALL(sys_ni_syscall) /* was sys_ssetmask */
+ /* 70 */ CALL(sys_setreuid16)
+ CALL(sys_setregid16)
+- CALL(sys_sigsuspend_wrapper)
++ CALL(sys_sigsuspend)
+ CALL(sys_sigpending)
+ CALL(sys_sethostname)
+ /* 75 */ CALL(sys_setrlimit)
+@@ -188,7 +188,7 @@
+ CALL(sys_rt_sigpending)
+ CALL(sys_rt_sigtimedwait)
+ CALL(sys_rt_sigqueueinfo)
+- CALL(sys_rt_sigsuspend_wrapper)
++ CALL(sys_rt_sigsuspend)
+ /* 180 */ CALL(ABI(sys_pread64, sys_oabi_pread64))
+ CALL(ABI(sys_pwrite64, sys_oabi_pwrite64))
+ CALL(sys_chown16)
+@@ -344,8 +344,8 @@
+ CALL(sys_readlinkat)
+ CALL(sys_fchmodat)
+ CALL(sys_faccessat)
+-/* 335 */ CALL(sys_ni_syscall) /* eventually pselect6 */
+- CALL(sys_ni_syscall) /* eventually ppoll */
++/* 335 */ CALL(sys_pselect6)
++ CALL(sys_ppoll)
+ CALL(sys_unshare)
+ CALL(sys_set_robust_list)
+ CALL(sys_get_robust_list)
+@@ -355,7 +355,7 @@
+ CALL(sys_vmsplice)
+ CALL(sys_move_pages)
+ /* 345 */ CALL(sys_getcpu)
+- CALL(sys_ni_syscall) /* eventually epoll_pwait */
++ CALL(sys_epoll_pwait)
+ CALL(sys_kexec_load)
+ CALL(sys_utimensat)
+ CALL(sys_signalfd)
+diff -rupN linux-2.6.31-rc6/arch/arm/kernel/entry-common.S linux-2.6.31-rc6.arm-restore-sigmask-v3/arch/arm/kernel/entry-common.S
+--- linux-2.6.31-rc6/arch/arm/kernel/entry-common.S 2009-08-14 11:11:10.000000000 +0200
++++ linux-2.6.31-rc6.arm-restore-sigmask-v3/arch/arm/kernel/entry-common.S 2009-08-14 11:26:44.000000000 +0200
+@@ -373,16 +373,6 @@ sys_clone_wrapper:
+ b sys_clone
+ ENDPROC(sys_clone_wrapper)
+
+-sys_sigsuspend_wrapper:
+- add r3, sp, #S_OFF
+- b sys_sigsuspend
+-ENDPROC(sys_sigsuspend_wrapper)
+-
+-sys_rt_sigsuspend_wrapper:
+- add r2, sp, #S_OFF
+- b sys_rt_sigsuspend
+-ENDPROC(sys_rt_sigsuspend_wrapper)
+-
+ sys_sigreturn_wrapper:
+ add r0, sp, #S_OFF
+ b sys_sigreturn
+diff -rupN linux-2.6.31-rc6/arch/arm/kernel/signal.c linux-2.6.31-rc6.arm-restore-sigmask-v3/arch/arm/kernel/signal.c
+--- linux-2.6.31-rc6/arch/arm/kernel/signal.c 2009-08-14 11:11:10.000000000 +0200
++++ linux-2.6.31-rc6.arm-restore-sigmask-v3/arch/arm/kernel/signal.c 2009-08-14 11:26:44.000000000 +0200
+@@ -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(¤t->sighand->siglock);
+- saveset = current->blocked;
++ current->saved_sigmask = current->blocked;
+ siginitset(¤t->blocked, mask);
+ recalc_sigpending();
+ spin_unlock_irq(¤t->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(¤t->sighand->siglock);
+- saveset = current->blocked;
+- current->blocked = newset;
+- recalc_sigpending();
+- spin_unlock_irq(¤t->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
+ /*
+ * 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
+
+ if (ret != 0) {
+ force_sigsegv(sig, tsk);
+- return;
++ return ret;
+ }
+
+ /*
+@@ -610,6 +575,7 @@ handle_signal(unsigned long sig, struct
+ recalc_sigpending();
+ spin_unlock_irq(&tsk->sighand->siglock);
+
++ return 0;
+ }
+
+ /*
+@@ -621,7 +587,7 @@ handle_signal(unsigned long sig, struct
+ * 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, s
+ * 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, s
+
+ 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 = ¤t->saved_sigmask;
++ else
++ oldset = ¤t->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, s
+ 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, ¤t->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(¤t->blocked, regs, syscall);
++ do_signal(regs, syscall);
+ }
+
+-------------------------------------------------------------------
+List admin: http://lists.arm.linux.org.uk/mailman/listinfo/linux-arm-kernel
+FAQ: http://www.arm.linux.org.uk/mailinglists/faq.php
+Etiquette: http://www.arm.linux.org.uk/mailinglists/etiquette.php
+
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