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authorChris Metcalf <cmetcalf@ezchip.com>2015-09-22 14:49:41 -0400
committerChris Metcalf <cmetcalf@ezchip.com>2016-01-18 14:49:09 -0500
commit583b24a210ada7e88fc12aaf50024975ec882816 (patch)
treeb396bc95a44f29d9dd2c8bab86fcd0d0728b24b1 /arch/tile/kernel/process.c
parent65a792e84f25d1436698f999224b2cf5d7594546 (diff)
downloadlinux-583b24a210ada7e88fc12aaf50024975ec882816.tar.bz2
arch/tile: adopt prepare_exit_to_usermode() model from x86
This change is a prerequisite change for TASK_ISOLATION but also stands on its own for readability and maintainability. The existing tile do_work_pending() was called in a loop from assembly on the slow path; this change moves the loop into C code as well. For the x86 version see commit c5c46f59e4e7 ("x86/entry: Add new, comprehensible entry and exit handlers written in C"). This change exposes a pre-existing bug on the older tilepro platform; the singlestep processing is done last, but on tilepro (unlike tilegx) we enable interrupts while doing that processing, so we could in theory miss a signal or other asynchronous event. A future change could fix this by breaking the singlestep work into a "prepare" step done in the main loop, and a "trigger" step done after exiting the loop. Since this change is intended as purely a restructuring change, we call out the bug explicitly now, but don't yet fix it. Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
Diffstat (limited to 'arch/tile/kernel/process.c')
-rw-r--r--arch/tile/kernel/process.c79
1 files changed, 41 insertions, 38 deletions
diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index 7d5769310bef..b5f30d376ce1 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -462,54 +462,57 @@ struct task_struct *__sched _switch_to(struct task_struct *prev,
/*
* This routine is called on return from interrupt if any of the
- * TIF_WORK_MASK flags are set in thread_info->flags. It is
- * entered with interrupts disabled so we don't miss an event
- * that modified the thread_info flags. If any flag is set, we
- * handle it and return, and the calling assembly code will
- * re-disable interrupts, reload the thread flags, and call back
- * if more flags need to be handled.
- *
- * We return whether we need to check the thread_info flags again
- * or not. Note that we don't clear TIF_SINGLESTEP here, so it's
- * important that it be tested last, and then claim that we don't
- * need to recheck the flags.
+ * TIF_ALLWORK_MASK flags are set in thread_info->flags. It is
+ * entered with interrupts disabled so we don't miss an event that
+ * modified the thread_info flags. We loop until all the tested flags
+ * are clear. Note that the function is called on certain conditions
+ * that are not listed in the loop condition here (e.g. SINGLESTEP)
+ * which guarantees we will do those things once, and redo them if any
+ * of the other work items is re-done, but won't continue looping if
+ * all the other work is done.
*/
-int do_work_pending(struct pt_regs *regs, u32 thread_info_flags)
+void prepare_exit_to_usermode(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 (WARN_ON(!user_mode(regs)))
+ return;
- user_exit();
+ do {
+ local_irq_enable();
- /* Enable interrupts; they are disabled again on return to caller. */
- local_irq_enable();
+ if (thread_info_flags & _TIF_NEED_RESCHED)
+ schedule();
- if (thread_info_flags & _TIF_NEED_RESCHED) {
- schedule();
- return 1;
- }
#if CHIP_HAS_TILE_DMA()
- if (thread_info_flags & _TIF_ASYNC_TLB) {
- do_async_page_fault(regs);
- return 1;
- }
+ if (thread_info_flags & _TIF_ASYNC_TLB)
+ do_async_page_fault(regs);
#endif
- if (thread_info_flags & _TIF_SIGPENDING) {
- do_signal(regs);
- return 1;
- }
- if (thread_info_flags & _TIF_NOTIFY_RESUME) {
- clear_thread_flag(TIF_NOTIFY_RESUME);
- tracehook_notify_resume(regs);
- return 1;
- }
- if (thread_info_flags & _TIF_SINGLESTEP)
+
+ if (thread_info_flags & _TIF_SIGPENDING)
+ do_signal(regs);
+
+ if (thread_info_flags & _TIF_NOTIFY_RESUME) {
+ clear_thread_flag(TIF_NOTIFY_RESUME);
+ tracehook_notify_resume(regs);
+ }
+
+ local_irq_disable();
+ thread_info_flags = READ_ONCE(current_thread_info()->flags);
+
+ } while (thread_info_flags & _TIF_WORK_MASK);
+
+ if (thread_info_flags & _TIF_SINGLESTEP) {
single_step_once(regs);
+#ifndef __tilegx__
+ /*
+ * FIXME: on tilepro, since we enable interrupts in
+ * this routine, it's possible that we miss a signal
+ * or other asynchronous event.
+ */
+ local_irq_disable();
+#endif
+ }
user_enter();
-
- return 0;
}
unsigned long get_wchan(struct task_struct *p)