Re: [PATCH] multithreaded coredumps for elf exeecutables for O(1) scheduler

[Mark Gross <mgross@unix-os.sc.intel.com>]

Thanks Vamsi, 

I'll add this to the next version of the patch.  

I've gotten a few comments about function names being too generic, and the 
fact that I'm holding too many locks in the resume_threads function.   Minor 
stuff but, I want to clean that up as well. 

--mgross

On Monday 13 May 2002 03:35 am, Vamsi Krishna S. wrote:
> Hi Mark,
>
> Despite other problems with ia64, stopping vm ops after the status (regs)
> of all the threads is captured, is a bug fix in generic code, and our patch
> effectively nukes that. Not a good thing. I had posted a patch on top of
> the previous tcore patch to fix this, I suppose it still applies to the
> 2.5.x patch. Please apply that (given here).
>
> Vamsi.
>
> Vamsi Krishna S.
> Linux Technology Center,
> IBM Software Lab, Bangalore.
> Ph: +91 80 5262355 Extn: 3959
> Internet: vamsi@in.ibm.com
>
> --- 2417-tcore/fs/binfmt_elf.c.ori	Thu Mar 21 15:30:08 2002
> +++ 2417-tcore/fs/binfmt_elf.c	Thu Mar 21 15:27:29 2002
> @@ -1289,10 +1289,6 @@
>  	int dump_threads = 0;
>  	int thread_status_size = 0;
>
> -	/* now stop all vm operations */
> -	down_write(&current->mm->mmap_sem);
> -	segs = current->mm->map_count;
> -
>   	if (atomic_read(&current->mm->mm_users) != 1) {
>  		dump_threads = core_dumps_threads;
>  	}
> @@ -1337,6 +1333,19 @@
>  		}
>  	} /* End if(dump_threads) */
>
> +	/*
> +	 * This transfers the registers from regs into the standard
> +	 * coredump arrangement, whatever that is. We need to do this
> +	 * before acquiring mmap_sem as on some architectures (IA64)
> +	 * we may need to access user pages to get register state.
> +	 */
> +	memset(&prstatus, 0, sizeof(prstatus));
> +	elf_core_copy_regs(&prstatus.pr_reg, regs);
> +
> +	/* now stop all vm operations */
> +	down_write(&current->mm->mmap_sem);
> +	segs = current->mm->map_count;
> +
>  #ifdef DEBUG
>  	printk("elf_core_dump: %d segs %lu limit\n", segs, limit);
>  #endif
> @@ -1358,16 +1367,9 @@
>  	 * Set up the notes in similar form to SVR4 core dumps made
>  	 * with info from their /proc.
>  	 */
> -	memset(&prstatus, 0, sizeof(prstatus));
>  	fill_prstatus(&prstatus, current, signr);
>  	fill_note(&notes[0], "CORE", NT_PRSTATUS, sizeof(prstatus), &prstatus);
>
> -	/*
> -	 * This transfers the registers from regs into the standard
> -	 * coredump arrangement, whatever that is.
> -	 */
> -	elf_core_copy_regs(&prstatus.pr_reg, regs);
> -
>  #ifdef DEBUG
>  	dump_regs("Passed in regs", (elf_greg_t *)regs);
>  	dump_regs("prstatus regs", (elf_greg_t *)&prstatus.pr_reg);
>
> On Fri, 10 May 2002 23:46:59 +0530, Mark Gross wrote:
> > ia64 requires more tweaks than just this to work.  This patch as it
> > stands isn't expected to work for ia64.
> >
> > Getting the register states for the note sections is more involved for
> > ia64 as well as the avoiding of patch collisions with  the diffs in
> > /pub/linux/kernel/ports/ia64/v2.5/
> >
> > I have an ia64 patch set thats partially tested for 2.4.17, that seems to
> > work. It didn't get posted as O(1) support became a bigger priority.
> >
> > I'm hoping to start updating the ia64 patch to support 2.5x very soon.
> >
> > --mgross
> >
> > On Friday 10 May 2002 01:13 pm, Manfred Spraul wrote:
> >> Have you checked that your patch doesn't deadlock on ia64?
> >>
> >> > +       /* First pause all related threaded processes */ +       if
> >> > (dump_threads)       {
> >> > +               suspend_threads();
> >> > +       }
> >> > +
> >> > +       /* now stop all vm operations */
> >> > +       down_write(&current->mm->mmap_sem); +       segs =
> >> > current->mm->map_count;
> >> > +
> >>
> >> Stopping all vm operations means that copy_{to,from}_user can cause
> >> deadlocks. ia64 needs copy_to_user in their stack unwind handler, IIRC
> >> called by ELF_CORE_COPY_REGS.
> >>
> >> Afaics you don't handle that. You must dump all thread state before
> >> down_write(mmap_sem). And I don't see how you protect against 2 threads
> >> of one process calling suspend_threads() simultaneously.
> >
> > -
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