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

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Message-ID: <20071220043429.GO4612@sgi.com>
Date:	Thu, 20 Dec 2007 15:34:29 +1100
From:	David Chinner <dgc@....com>
To:	Kyle McMartin <kyle@...artin.ca>
Cc:	David Chinner <dgc@....com>, lkml <linux-kernel@...r.kernel.org>,
	tony.luck@...el.com, linux-ia64@...r.kernel.org
Subject: Re: [ia64] BUG: sleeping in atomic

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?
> 
> 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.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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