Add TIF_FD_SLOTS and test it on the untraced return from a system
call. A task that reserved descriptors takes the tracesys_exit path,
where syscall_trace_exit() commits them before the ptrace exit stop.
The traced path already ends up there.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 arch/arc/include/asm/thread_info.h | 2 ++
 arch/arc/kernel/entry.S            | 5 +++++
 arch/arc/kernel/ptrace.c           | 4 ++++
 3 files changed, 11 insertions(+)

diff --git a/arch/arc/include/asm/thread_info.h b/arch/arc/include/asm/thread_info.h
index 255d2c774219..4c67d4eb434b 100644
--- a/arch/arc/include/asm/thread_info.h
+++ b/arch/arc/include/asm/thread_info.h
@@ -77,6 +77,7 @@ static inline __attribute_const__ struct thread_info *current_thread_info(void)
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_SYSCALL_AUDIT	4	/* syscall auditing active */
 #define TIF_NOTIFY_SIGNAL	5	/* signal notifications exist */
+#define TIF_FD_SLOTS		6	/* syscall prepared descriptors */
 #define TIF_SYSCALL_TRACE	15	/* syscall trace active */
 /* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		16
@@ -88,6 +89,7 @@ static inline __attribute_const__ struct thread_info *current_thread_info(void)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_NOTIFY_SIGNAL	(1<<TIF_NOTIFY_SIGNAL)
+#define _TIF_FD_SLOTS		(1<<TIF_FD_SLOTS)
 #define _TIF_MEMDIE		(1<<TIF_MEMDIE)
 #define _TIF_SYSCALL_TRACEPOINT	(1<<TIF_SYSCALL_TRACEPOINT)
 
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index 3c7e74aba679..f436391526e1 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -241,6 +241,11 @@ ENTRY(EV_Trap)
 	jl      [r9]
 
 .Lret_from_system_call:
+	; descriptors reserved by the syscall are committed in syscall_trace_exit()
+	GET_CURR_THR_INFO_FLAGS   r10
+	and.f 0, r10, _TIF_FD_SLOTS
+	bnz   tracesys_exit
+
 	st  r0, [sp, PT_r0]     ; sys call return value in pt_regs
 
 	; fall through to ret_from_exception
diff --git a/arch/arc/kernel/ptrace.c b/arch/arc/kernel/ptrace.c
index fe2b6572e919..0a0d74b9c7c4 100644
--- a/arch/arc/kernel/ptrace.c
+++ b/arch/arc/kernel/ptrace.c
@@ -3,6 +3,7 @@
  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
  */
 
+#include <linux/file.h>
 #include <linux/ptrace.h>
 #include <linux/sched/task_stack.h>
 #include <linux/regset.h>
@@ -355,6 +356,9 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs)
 
 asmlinkage void syscall_trace_exit(struct pt_regs *regs)
 {
+	if (test_thread_flag(TIF_FD_SLOTS))
+		fd_slots_commit(regs);
+
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
 		ptrace_report_syscall_exit(regs, 0);
 

-- 
2.53.0