David Chinner wrote:
> On Wed, Dec 19, 2007 at 11:42:04AM -0500, Kyle McMartin wrote:
>
>> On Wed, Dec 19, 2007 at 04:54:30PM +1100, David Chinner wrote:
>>
>>> [ 5667.086055] BUG: sleeping function called from invalid context at
>>> kernel/fork.c:401
>>>
>>>
>> The problem is that mmput is called under the read_lock by
>> find_thread_for_addr... The comment above seems to indicate that gdb
>> needs to be able to access any child tasks register backing store
>> memory... This seems pretty broken.
>>
>> cheers, Kyle
>>
>> ---
>>
>> Who knows, maybe gdb is saner now?
>>
Well, gdb is saner, but the bug you're talking about will be fixed in a
clean way (even for insane debuggers) with Shaohua's, Roland's and my
fixes to handling the RSE, because they make it possible to get rid of
find_thread_for_addr(). I already sent a mail about it to linux-ia64
some time ago, and Roland suggested we might even change everything to
the generic sys_ptrace(), which is the correct solution (TM), and I'm
planning to do it so as soon as the RSE patches are in.
Regards,
Petr Tesarik
>> diff --git a/arch/ia64/kernel/ptrace.c b/arch/ia64/kernel/ptrace.c
>> index 2e96f17..b609704 100644
>> --- a/arch/ia64/kernel/ptrace.c
>> +++ b/arch/ia64/kernel/ptrace.c
>> @@ -1418,7 +1418,7 @@ asmlinkage long
>> sys_ptrace (long request, pid_t pid, unsigned long addr, unsigned long data)
>> {
>> struct pt_regs *pt;
>> - unsigned long urbs_end, peek_or_poke;
>> + unsigned long urbs_end;
>> struct task_struct *child;
>> struct switch_stack *sw;
>> long ret;
>> @@ -1430,23 +1430,12 @@ sys_ptrace (long request, pid_t pid, unsigned long
>> addr, unsigned long data)
>> goto out;
>> }
>>
>> - peek_or_poke = (request == PTRACE_PEEKTEXT
>> - || request == PTRACE_PEEKDATA
>> - || request == PTRACE_POKETEXT
>> - || request == PTRACE_POKEDATA);
>> - ret = -ESRCH;
>> - read_lock(&tasklist_lock);
>> - {
>> - child = find_task_by_pid(pid);
>> - if (child) {
>> - if (peek_or_poke)
>> - child = find_thread_for_addr(child, addr);
>> - get_task_struct(child);
>> - }
>> - }
>> - read_unlock(&tasklist_lock);
>> - if (!child)
>> + child = ptrace_get_task_struct(pid);
>> + if (IS_ERR(child)) {
>> + ret = PTR_ERR(child);
>> goto out;
>> + }
>> +
>> ret = -EPERM;
>> if (pid == 1) /* no messing around with init! */
>> goto out_tsk;
>>
>
> Yes, this patch fixes the problem (though I haven't tried to
> use gdb yet).
>
> Cheers,
>
> Dave.
>
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