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Messages in this thread Complete thread (EXPERIMENTAL) |
On Wed, 7 May 2008, Andrew Morton wrote: Now, if we need to take both anon_vma->lock AND i_mmap_lock in the newly added mm_lock() thing and we also take both those locks at the same time in regular code, we're probably screwed. No, just use the normal static ordering for that case: one type of lock goes before the other kind. If those locks nest in regular code, you have to do that *anyway*. The code that can take many locks, will have to get the global lock *and* order the types, but that's still trivial. It's something like spin_lock(&global_lock); for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (vma->anon_vma)
spin_lock(&vma->anon_vma->lock);
}
for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (!vma->anon_vma && vma->vm_file && vma->vm_file->f_mapping)
spin_lock(&vma->vm_file->f_mapping->i_mmap_lock);
}
spin_unlock(&global_lock);
and now everybody follows the rule that "anon_vma->lock" precedes
"i_mmap_lock". So there can be no ABBA deadlock between the normal users
and the many-locks version, and there can be no ABBA deadlock between
many-locks-takers because they use the global_lock to serialize.
This really isn't rocket science, guys. (I really hope and believe that they don't nest anyway, and that you can just use a single for-loop for the many-lock case) Linus | ||||||||||
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