arch/tile: fix up some issues in calling do_work_pending()

First, we were at risk of handling thread-info flags, in particular
do_signal(), when returning from kernel space.  This could happen
after a failed kernel_execve(), or when forking a kernel thread.
The fix is to test in do_work_pending() for user_mode() and return
immediately if so; we already had this test for one of the flags,
so I just hoisted it to the top of the function.

Second, if a ptraced process updated the callee-saved registers
in the ptregs struct and then processed another thread-info flag, we
would overwrite the modifications with the original callee-saved
registers.  To fix this, we add a register to note if we've already
saved the registers once, and skip doing it on additional passes
through the loop.  To avoid a performance hit from the couple of
extra instructions involved, I modified the GET_THREAD_INFO() macro
to be guaranteed to be one instruction, then bundled it with adjacent
instructions, yielding an overall net savings.

Reported-By: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index 2d5ef61..54e6c64 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -567,6 +567,10 @@ struct task_struct *__sched _switch_to(struct task_struct *prev,
  */
 int do_work_pending(struct pt_regs *regs, u32 thread_info_flags)
 {
+	/* If we enter in kernel mode, do nothing and exit the caller loop. */
+	if (!user_mode(regs))
+		return 0;
+
 	if (thread_info_flags & _TIF_NEED_RESCHED) {
 		schedule();
 		return 1;
@@ -589,8 +593,7 @@ int do_work_pending(struct pt_regs *regs, u32 thread_info_flags)
 		return 1;
 	}
 	if (thread_info_flags & _TIF_SINGLESTEP) {
-		if ((regs->ex1 & SPR_EX_CONTEXT_1_1__PL_MASK) == 0)
-			single_step_once(regs);
+		single_step_once(regs);
 		return 0;
 	}
 	panic("work_pending: bad flags %#x\n", thread_info_flags);