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charset="UTF-8" X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 71EC4180010 X-Stat-Signature: 4o6wgoekmwqgikswn7zxmkty956ij6sh X-Rspam-User: X-HE-Tag: 1673980004-958812 X-HE-Meta: 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 VXOj36Q9 E9S+8kO2nlCAYP2L77hJB0PubXAnJMWxA0qGu7KSNv8rl/9BFY8OCsouqKg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jan 17, 2023 at 10:12 AM Jann Horn wrote: > > On Mon, Jan 9, 2023 at 9:55 PM Suren Baghdasaryan wrote: > > rw_semaphore is a sizable structure of 40 bytes and consumes > > considerable space for each vm_area_struct. However vma_lock has > > two important specifics which can be used to replace rw_semaphore > > with a simpler structure: > [...] > > static inline void vma_read_unlock(struct vm_area_struct *vma) > > { > > - up_read(&vma->vm_lock->lock); > > + if (atomic_dec_and_test(&vma->vm_lock->count)) > > + wake_up(&vma->vm_mm->vma_writer_wait); > > } > > I haven't properly reviewed this, but this bit looks like a > use-after-free because you're accessing the vma after dropping your > reference on it. You'd have to first look up the vma->vm_mm, then do > the atomic_dec_and_test(), and afterwards do the wake_up() without > touching the vma. Or alternatively wrap the whole thing in an RCU > read-side critical section if the VMA is freed with RCU delay. vm_lock->count does not control the lifetime of the VMA, it's a counter of how many readers took the lock or it's negative if the lock is write-locked.