| Message ID | 0b13e0e24ec0307d67ab7a23b58764f6b1270116.1409954077.git.luto@amacapital.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 39296d25708c..bbf338a04a5d 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -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(); /* * If we stepped into a sysenter/syscall insn, it trapped in
The RCU context tracking code requires that arch code call user_exit() on any entry into kernel code if TIF_NOHZ is set. This patch adds a check for TIF_NOHZ and a comment to the syscall entry tracing code. The main purpose of this patch is to make the code easier to follow: one can read the body of user_exit and of every function it calls without finding any explanation of why it's called for traced syscalls but not for untraced syscalls. This makes it clear when user_exit() is necessary. Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Andy Lutomirski <luto@amacapital.net> --- arch/x86/kernel/ptrace.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)