[lkml]   [2008]   [May]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 08 of 11] anon-vma-rwsem

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

for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (vma->anon_vma)
for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (!vma->anon_vma && vma->vm_file && vma->vm_file->f_mapping)

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)


 \ /
  Last update: 2008-05-08 01:23    [W:0.095 / U:9.636 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site