[PATCH v4 2/5] x86,entry: Only call user_exit if TIF_NOHZ
From: oleg@redhat.com (Oleg Nesterov)
Date: 2014-07-29 19:34:48
Also in:
linux-arch, linux-mips, lkml
On 07/28, Andy Lutomirski wrote:
quoted hunk ↗ jump to hunk
@@ -1449,7 +1449,12 @@ long syscall_trace_enter(struct pt_regs *regs) { long ret = 0; - user_exit(); + /* + * If TIF_NOHZ is set, we are required to call user_exit() before + * doing anything that could touch RCU. + */ + if (test_thread_flag(TIF_NOHZ)) + user_exit();
Personally I still think this change just adds more confusion, but I leave this to you and Frederic. It is not that "If TIF_NOHZ is set, we are required to call user_exit()", we need to call user_exit() just because we enter the kernel. TIF_NOHZ is just the implementation detail which triggers this slow path. At least it should be correct, unless I am confused even more than I think. Oleg.