Re: locking question: do_mmap(), do_munmap()

Stephen C. Tweedie
1999-10-11T22:22:42Z

Hi,

On Mon, 11 Oct 1999 20:02:40 +0200, Manfred Spraul
<manfreds@colorfullife.com> said:

> What about something like a rw-semaphore which protects the vma list:
> vma-list modifiers [ie merge_segments(), insert_vm_struct() and
> do_munmap()] grab it exclusive, swapper grabs it "shared, starve
> exclusive".

Deadlock. Process A tries to do an mmap on mm A, gets the exclusive
lock, tries to swap out from process B, and grabs mm B's shared lock.
Process B in the mean time is doing the same thing and has an exclusive
lock on mm B, and is trying to share-lock A. Whoops.

> This should not dead-lock,

Are you sure?!

--Stephen