On Wed, Jun 5, 2024 at 6:33 AM Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> wrote: > > * Matthew Wilcox <willy@xxxxxxxxxxxxx> [240604 20:57]: > > On Tue, Jun 04, 2024 at 05:24:46PM -0700, Andrii Nakryiko wrote: > > > +/* > > > + * find_and_lock_vma_rcu() - Find and lock the VMA for a given address, or the > > > + * next VMA. Search is done under RCU protection, without taking or assuming > > > + * mmap_lock. Returned VMA is guaranteed to be stable and not isolated. > > > > You know this is supposed to be the _short_ description, right? > > Three lines is way too long. The full description goes between the > > arguments and the Return: line. Sure, I'll adjust. > > > > > + * @mm: The mm_struct to check > > > + * @addr: The address > > > + * > > > + * Returns: The VMA associated with addr, or the next VMA. > > > + * May return %NULL in the case of no VMA at addr or above. > > > + * If the VMA is being modified and can't be locked, -EBUSY is returned. > > > + */ > > > +struct vm_area_struct *find_and_lock_vma_rcu(struct mm_struct *mm, > > > + unsigned long address) > > > +{ > > > + MA_STATE(mas, &mm->mm_mt, address, address); > > > + struct vm_area_struct *vma; > > > + int err; > > > + > > > + rcu_read_lock(); > > > +retry: > > > + vma = mas_find(&mas, ULONG_MAX); > > > + if (!vma) { > > > + err = 0; /* no VMA, return NULL */ > > > + goto inval; > > > + } > > > + > > > + if (!vma_start_read(vma)) { > > > + err = -EBUSY; > > > + goto inval; > > > + } > > > + > > > + /* > > > + * Check since vm_start/vm_end might change before we lock the VMA. > > > + * Note, unlike lock_vma_under_rcu() we are searching for VMA covering > > > + * address or the next one, so we only make sure VMA wasn't updated to > > > + * end before the address. > > > + */ > > > + if (unlikely(vma->vm_end <= address)) { > > > + err = -EBUSY; > > > + goto inval_end_read; > > > + } > > > + > > > + /* Check if the VMA got isolated after we found it */ > > > + if (vma->detached) { > > > + vma_end_read(vma); > > > + count_vm_vma_lock_event(VMA_LOCK_MISS); > > > + /* The area was replaced with another one */ > > > > Surely you need to mas_reset() before you goto retry? > > Probably more than that. We've found and may have adjusted the > index/last; we should reconfigure the maple state. You should probably > use mas_set(), which will reset the maple state and set the index and > long to address. Yep, makes sense, thanks. As for the `unlikely(vma->vm_end <= address)` case, I presume we want to do the same, right? Basically, on each retry start from the `address` unconditionally, no matter what's the reason for retry. > > > > > > > + goto retry; > > > + } > >