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 <[email protected]> Reported-by: Sergey Senozhatsky <[email protected]> Signed-off-by: Frederic Weisbecker <[email protected]> --- arch/x86/kernel/ptrace.c | 7 +++++++ 1 files changed, 7 insertions(+), 0 deletions(-) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index b00b33a..eff5b8c 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))) -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
