From 2c5594df344cd1ff0cc9bf007dea3235582b3acf Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 26 Oct 2012 11:40:28 +0200 Subject: [PATCH] rcu: Fix unrecovered RCU user mode in syscall_trace_leave() On x86-64 syscall exit, 3 non exclusive events may happen looping in the following order: 1) Check if we need resched for user preemption, if so call schedule_user() 2) Check if we have pending signals, if so call do_notify_resume() 3) Check if we do syscall tracing, if so call syscall_trace_leave() However syscall_trace_leave() has been written assuming it directly follows the syscall and forget about the above possible 1st and 2nd steps. Now schedule_user() and do_notify_resume() exit in RCU user mode because they have most chances to resume userspace immediately and this avoids an rcu_user_enter() call in the syscall fast path. So by the time we call syscall_trace_leave(), we may well be in RCU user mode. To fix this up, simply call rcu_user_exit() in the beginning of this function. This fixes some reported RCU uses in extended quiescent state. Reported-by: Dave Jones Reported-by: Sergey Senozhatsky Signed-off-by: Frederic Weisbecker Tested-by: Sergey Senozhatsky Signed-off-by: Paul E. McKenney --- arch/x86/kernel/ptrace.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index b00b33a183908b..eff5b8c68652d5 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -1511,6 +1511,13 @@ void syscall_trace_leave(struct pt_regs *regs) { bool step; + /* + * We may come here right after calling schedule_user() + * or do_notify_resume(), in which case we can be in RCU + * user mode. + */ + rcu_user_exit(); + audit_syscall_exit(regs); if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))