Re: [PATCH] multithreaded coredumps for elf exeecutables

From: Daniel Jacobowitz (dan@debian.org)
Date: Wed Mar 20 2002 - 13:37:09 EST

On Wed, Mar 20, 2002 at 11:36:30AM +0530, Vamsi Krishna S . wrote:
> There is serialization at higher level. We take a write lock
> on current->mm->mmap_sem at the beginning of elf_core_dump
> function which is released just before leaving the function.
> So, if one thread enters elf_core_dump and starts dumping core,
> no other thread (same mm) of the same process can start
> dumping.
>
> static int elf_core_dump(long signr, struct pt_regs * regs, struct file * file)
> {
> ...
> ...
> /* now stop all vm operations */
> down_write(&current->mm->mmap_sem);
> ...
> ...
> ...
> up_write(&current->mm->mmap_sem);
> return has_dumped;
> }

That's not a feature, it's a bug. You can't take the mmap_sem before
collecting thread status; it will cause a deadlock on at least ia64,
where some registers are collected from user memory.

(Thanks to Manfred Spraul for explaining that to me.) 

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer
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