[patch][RFC] an early patch for x86_64 preempt-rt kernel cause more __might_sleep warnings

[hyl <heyongli@gmail.com>]

Hi, John

[Sorry resend this mail, with pure text format and CC to Linux-kernel. ]

I saw you submitted a patch for X86_64 to prevent a oops, here is the
hyper-link i google:
http://marc.info/?l=git-commits-head&m=113979973412652&w=2

There is an obvious problem for your patch , see my comment at  "=====>"

/* runs on IST stack. */
asmlinkage void __kprobes do_debug(struct pt_regs * regs,
                   unsigned long error_code)
{

- conditional_sti(regs);
+ preempt_conditional_sti(regs);


       force_sig_info(SIGTRAP, &info, tsk);=====> /*this function try
spin_lock_irqsave(&t->sighand->siglock, flags); generate more
warnings*/


clear_dr7:
set_debugreg(0UL, 7);
+ preempt_conditional_cli(regs);
return;

clear_TF_reenable:
set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
regs->eflags &= ~TF_MASK;
+ preempt_conditional_cli(regs);

}


here is the trace result, founded on linux2.6.25.4 with realtime
patch(not only do_debug, do_int3,do_stack_segment also has same
problem ):

BUG: sleeping function called from invalid context
usermode-agent(2302) at kernel/rtmutex.c:626

in_atomic():1 [00000001], irqs_disabled():0

Call Trace:
<#DB>  [<ffffffff80227177>] __might_sleep+0x107/0x110
[<ffffffff804ec510>] __rt_spin_lock+0x30/0x60
[<ffffffff804ec549>] rt_spin_lock+0x9/0x10

[<ffffffff8023cf2f>] force_sig_info+0x2f/0xd0
[<ffffffff8020cdab>] do_debug+0x17b/0x220
[<ffffffff804ed1b3>] debug+0x93/0x9f
<<EOE>>

Posssible way to resolve such problem:

1. relpace task->sighand->siglock  as raw_spin_lock_t
    but this will  reduce the preemptive kernel code size

2. if possible, call  preempt_conditional_cli before call force_sig_info
    but we must sure the John's bug not be re-introduce by such action

please don't hesitate to tell me the best solution if you got the good idea.


Best Wishes
hyl