Re: PATCH Multithreaded core dumps for the 2.5.17 kernel was ....RE: PATCH Multithreaded core dump support for the 2.5.14 (and 15) kernel.

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

On Wednesday 22 May 2002 07:32 pm, Daniel Jacobowitz wrote:
>
> What about other things which take mmap_sem?  I believe at least ptrace
> is involved.  The notion of avoiding taking a semaphore like this is a
> somewhat risky one.

Yes access_process_vm down_writes the mmap_sem.  However; it can only read 
and write to existing user pages.  As long as it doesn't delete any of them 
its not a problem.  It won't cause a dead lock or panic during the core dump 
processing if this happens.  

The only process I know that could honestly use this ptrace function is GDB 
doing live debugging.

>
> Why shouldn't you take the semaphore as before in elf_core_dump, if you
> know that no suspended process has it - which you do if you hold it
> while suspending them?

For Ia64 those down_writes are just a pain.  If a user application is 
crashing because someone is being rude with GDB corrupting its user pages 
then I don't think its worth the hassle of protecting the core dumped user 
page mm data from being messed up by a GDB user.

I would like to leave the down_write out of elf_core_dump, but it could be 
put back if its felt that its needed.

Opinions? Comments?

--mgross