Re: Deadlock on the mm->mmap_sem

Andrea Arcangeli
2001-09-20T08:09:37Z

On Thu, Sep 20, 2001 at 09:01:13AM +0100, David Howells wrote:
>
> Andrea Arcangeli <andrea@suse.de> wrote:
> > the process doesn't need to lock multiple mm_structs at the same time.
>
> fork, ptrace, /proc/pid/mem, /proc/pid/maps
>
> All have to be able to lock two process's mm_structs simultaneously, even if
> it's indirectly through copy_to_user() or copy_from_user().

ptrace doesn't use down_read_recursive, nor /proc/<>/mem, nor fork.

for /proc/<pid>/maps this check takes care of it of course (or it could
get unfair again: only when we're faulting on our vm we're allowed to go
through):

if (task == current)
down_read_recursive(&mm->mmap_sem, &current->mm_recursor);
else
down_read(&mm->mmap_sem);

Andrea