Messages in this thread | | | From | Mark Gross <> | Subject | 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. | Date | Wed, 22 May 2002 17:09:01 -0400 |
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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
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