Messages in this thread Patch in this message | | | Date | Thu, 13 Mar 2014 16:32:18 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH -next] mm,vmacache: also flush cache for VM_CLONE |
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On 03/13, Oleg Nesterov wrote: > > Yes. But it seems that use_mm() and unuse_mm() should invalidate vmacache too. > > Suppose that a kernel thread T does, say, > > use_mm(foreign_mm); > get_user(...); > unuse_mm(); > > This can trigger a fault and populate T->vmacache[]. If this code is called > again vmacache_find() can use the stale entries. > > Or, assuming that only a kernel thread can do use_mm(), we can change > vmacache_valid() to also check !PF_KTHREAD.
Yes, I think we should check PF_KTHREAD, because
> Hmm. Another problem is that use_mm() doesn't take ->mmap_sem and thus > it can race with vmacache_flush_all()...
this also closes this race. use_mm() users should not use vmacache at all.
> Finally. Shouldn't vmacache_update() check current->mm == mm as well? > What if access_remote_vm/get_user_pages trigger find_vma() ??? Unless > I missed something this is not theoretical at all and can lead to the > corrupted vmacache, no?
Looks like a real problem or I am totally confused. I think we need something like below (uncompiled).
Oleg.
--- x/mm/vmacache.c +++ x/mm/vmacache.c @@ -30,20 +30,24 @@ void vmacache_flush_all(struct mm_struct rcu_read_unlock(); } +static bool vmacache_valid_mm(mm) +{ + return current->mm == mm && !(current->flags & PF_KTHREAD); +} + void vmacache_update(unsigned long addr, struct vm_area_struct *newvma) { - int idx = VMACACHE_HASH(addr); - current->vmacache[idx] = newvma; + if (vmacache_valid_mm(newvma->vm_mm)) + current->vmacache[VMACACHE_HASH(addr)] = newvma; } static bool vmacache_valid(struct mm_struct *mm) { - struct task_struct *curr = current; - - if (mm != curr->mm) + if (!vmacache_valid_mm(mm)) return false; if (mm->vmacache_seqnum != curr->vmacache_seqnum) { + struct task_struct *curr = current; /* * First attempt will always be invalid, initialize * the new cache for this task here.
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