[PATCH RFC 05/28] ARM: process: Remove local restart

[Linus Walleij]

The ARM kernel contains a quirk to handle syscall restarts
inside the kernel without exiting to userspace. The generic
entry cannot handle this.

Rename do_signal() to arch_do_signal_or_restart() to fit
with the upcoming generic entry conversion.

This is essentially a revert of commit 81783786d5cf
"ARM: 7473/1: deal with handlerless restarts without leaving the kernel"
from 2012.

Other solutions may be possible, such as checking the PC after
do_work_pending and assume it is a local restart if that address
is inside the kernel, or modifying the generic entry code to
track local restarts like ARM does and pass that information
back.

Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
---
 arch/arm/include/asm/signal.h  |  3 +--
 arch/arm/kernel/entry-common.S |  9 +--------
 arch/arm/kernel/signal.c       | 28 +++++++++-------------------
 3 files changed, 11 insertions(+), 29 deletions(-)

diff --git a/arch/arm/include/asm/signal.h b/arch/arm/include/asm/signal.h
index 8b84092d1518..7acccc96840c 100644
--- a/arch/arm/include/asm/signal.h
+++ b/arch/arm/include/asm/signal.h
@@ -24,7 +24,6 @@ typedef struct {
 #include <asm/sigcontext.h>
 
 void do_rseq_syscall(struct pt_regs *regs);
-int do_work_pending(struct pt_regs *regs, unsigned int thread_flags,
-		    int syscall);
+void do_work_pending(struct pt_regs *regs, unsigned int thread_flags);
 
 #endif
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index df6961a1006b..da5c2d4b62e5 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -86,14 +86,8 @@ ENDPROC(ret_fast_syscall)
 	bne	__sys_trace_return_nosave
 slow_work_pending:
 	mov	r0, sp				@ 'regs'
-	mov	r2, why				@ 'syscall'
 	bl	do_work_pending
-	cmp	r0, #0
-	beq	no_work_pending
-	movlt	scno, #(__NR_restart_syscall - __NR_SYSCALL_BASE)
-	str	scno, [tsk, #TI_ABI_SYSCALL]	@ make sure tracers see update
-	ldmia	sp, {r0 - r6}			@ have to reload r0 - r6
-	b	local_restart			@ ... and off we go
+	b	no_work_pending
 ENDPROC(ret_fast_syscall)
 
 /*
@@ -266,7 +260,6 @@ ENTRY(vector_swi)
 	 */
  TRACE(	ldmia	sp, {r0 - r3}		)
 
-local_restart:
 	ldr	r10, [tsk, #TI_FLAGS]		@ check for syscall tracing
 	stmdb	sp!, {r4, r5}			@ push fifth and sixth args
 
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 79a6730fa0eb..7b1a16e86b23 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -18,6 +18,7 @@
 #include <asm/traps.h>
 #include <asm/unistd.h>
 #include <asm/vfp.h>
+#include <asm/syscall.h>
 #include <asm/syscalls.h>
 
 #include "signal.h"
@@ -534,9 +535,10 @@ static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
  * 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(struct pt_regs *regs, int syscall)
+static void arch_do_signal_or_restart(struct pt_regs *regs)
 {
 	unsigned int retval = 0, continue_addr = 0, restart_addr = 0;
+	bool syscall = (syscall_get_nr(current, regs) != -1);
 	struct ksignal ksig;
 	int restart = 0;
 
@@ -590,16 +592,14 @@ static int do_signal(struct pt_regs *regs, int syscall)
 	} else {
 		/* no handler */
 		restore_saved_sigmask();
-		if (unlikely(restart) && regs->ARM_pc == restart_addr) {
+		if (unlikely(restart) && regs->ARM_pc == restart_addr)
 			regs->ARM_pc = continue_addr;
-			return restart;
-		}
 	}
-	return 0;
+	return;
 }
 
-asmlinkage int
-do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
+asmlinkage void
+do_work_pending(struct pt_regs *regs, unsigned int thread_flags)
 {
 	/*
 	 * The assembly code enters us with IRQs off, but it hasn't
@@ -612,19 +612,10 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 			schedule();
 		} else {
 			if (unlikely(!user_mode(regs)))
-				return 0;
+				return;
 			local_irq_enable();
 			if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) {
-				int restart = do_signal(regs, syscall);
-				if (unlikely(restart)) {
-					/*
-					 * Restart without handlers.
-					 * Deal with it without leaving
-					 * the kernel space.
-					 */
-					return restart;
-				}
-				syscall = 0;
+				arch_do_signal_or_restart(regs);
 			} else if (thread_flags & _TIF_UPROBE) {
 				uprobe_notify_resume(regs);
 			} else {
@@ -634,7 +625,6 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 		local_irq_disable();
 		thread_flags = read_thread_flags();
 	} while (thread_flags & _TIF_WORK_MASK);
-	return 0;
 }
 
 struct page *get_signal_page(void)

-- 
2.46.2