linux-kernel - Re: [ia64] BUG: sleeping in atomic

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Message-ID: <476B7623.3040008@suse.cz>
Date:	Fri, 21 Dec 2007 09:15:31 +0100
From:	Petr Tesarik <ptesarik@...e.cz>
To:	David Chinner <dgc@....com>
CC:	Kyle McMartin <kyle@...artin.ca>,
	lkml <linux-kernel@...r.kernel.org>, tony.luck@...el.com,
	linux-ia64@...r.kernel.org
Subject: Re: [ia64] BUG: sleeping in atomic

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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