[PATCH RFC 21/28] ARM: entry: Do not double-call exit functions

[Linus Walleij]

This is a semantic change to ret_fast_syscall: if there is no
work pending the function used to jump to ret_to_user, instead
we proceed to return from the syscall.

If we jump to ret_to_user, IRQs are enabled and we call
syscall_exit_to_user_mode a second time; at this point a
this just means a second call to rseq_syscall(), but it
seems wrong and we want syscall_exit_to_user_mode to be called
exactly once.

Apparently the ARM kernel has under some circumstances called
rseq_syscall() twice on the exit to userspace without side effects.

ret_to_user also checks for pending work a second time under
ret_to_user_from_irq, but this isn't even needed any more on
the fast return path: this was needed because the syscall
invocation enabled interrupts when doing syscall tracing, and
all tracing invocation has been moved over to C in earlier
patches.

Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
---
 arch/arm/kernel/entry-common.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index ece921571714..33bc9e7c5b32 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -49,7 +49,7 @@ ret_fast_syscall:
 	tst	r1, #_TIF_SYSCALL_WORK
 	beq	1f
 
-	b	ret_to_user
+	b	2f
 
 1:	mov	r0, sp				@ 'regs'
 	bl	do_work_pending

-- 
2.46.2