path: root/arch/s390/include/asm/syscall.h
diff options
authorMartin Schwidefsky <>2011-10-30 15:16:47 +0100
committerMartin Schwidefsky <>2011-10-30 15:16:43 +0100
commit20b40a794baf3b4b0320c0a77ce944d5d1a01f25 (patch)
treefb5eb62f8f75d8f6a31aae4c3cff3371f41cdd6d /arch/s390/include/asm/syscall.h
parent3ee49c8f123257c72b74f398ef99ac3348c493cc (diff)
[S390] signal race with restarting system calls
For a ERESTARTNOHAND/ERESTARTSYS/ERESTARTNOINTR restarting system call do_signal will prepare the restart of the system call with a rewind of the PSW before calling get_signal_to_deliver (where the debugger might take control). For A ERESTART_RESTARTBLOCK restarting system call do_signal will set -EINTR as return code. There are two issues with this approach: 1) strace never sees ERESTARTNOHAND, ERESTARTSYS, ERESTARTNOINTR or ERESTART_RESTARTBLOCK as the rewinding already took place or the return code has been changed to -EINTR 2) if get_signal_to_deliver does not return with a signal to deliver the restart via the repeat of the svc instruction is left in place. This opens a race if another signal is made pending before the system call instruction can be reexecuted. The original system call will be restarted even if the second signal would have ended the system call with -EINTR. These two issues can be solved by dropping the early rewind of the system call before get_signal_to_deliver has been called and by using the TIF_RESTART_SVC magic to do the restart if no signal has to be delivered. The only situation where the system call restart via the repeat of the svc instruction is appropriate is when a SA_RESTART signal is delivered to user space. Unfortunately this breaks inferior calls by the debugger again. The system call number and the length of the system call instruction is lost over the inferior call and user space will see ERESTARTNOHAND/ ERESTARTSYS/ERESTARTNOINTR/ERESTART_RESTARTBLOCK. To correct this a new ptrace interface is added to save/restore the system call number and system call instruction length. Signed-off-by: Martin Schwidefsky <>
Diffstat (limited to 'arch/s390/include/asm/syscall.h')
1 files changed, 3 insertions, 2 deletions
diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h
index 5c0246b955d8..614267f60713 100644
--- a/arch/s390/include/asm/syscall.h
+++ b/arch/s390/include/asm/syscall.h
@@ -13,6 +13,7 @@
#define _ASM_SYSCALL_H 1
#include <linux/sched.h>
+#include <linux/err.h>
#include <asm/ptrace.h>
@@ -25,7 +26,7 @@ extern const unsigned int sys_call_table[];
static inline long syscall_get_nr(struct task_struct *task,
struct pt_regs *regs)
- return regs->svcnr ? regs->svcnr : -1;
+ return regs->svc_code ? (regs->svc_code & 0xffff) : -1;
static inline void syscall_rollback(struct task_struct *task,
@@ -37,7 +38,7 @@ static inline void syscall_rollback(struct task_struct *task,
static inline long syscall_get_error(struct task_struct *task,
struct pt_regs *regs)
- return (regs->gprs[2] >= -4096UL) ? -regs->gprs[2] : 0;
+ return IS_ERR_VALUE(regs->gprs[2]) ? regs->gprs[2] : 0;
static inline long syscall_get_return_value(struct task_struct *task,