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charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 61A3814000C X-Stat-Signature: gbe85xhf855manrxs8zh3fheudwudshy X-HE-Tag: 1673990922-249266 X-HE-Meta: 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 SqeDO1Ch oQdxDSZfcveYelDo= 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 10:03 AM Jann Horn wrote: > > +locking maintainers Thanks! I'll CC the locking maintainers in the next posting. > > On Mon, Jan 9, 2023 at 9:54 PM Suren Baghdasaryan wrote: > > Introduce a per-VMA rw_semaphore to be used during page fault handling > > instead of mmap_lock. Because there are cases when multiple VMAs need > > to be exclusively locked during VMA tree modifications, instead of the > > usual lock/unlock patter we mark a VMA as locked by taking per-VMA lock > > exclusively and setting vma->lock_seq to the current mm->lock_seq. When > > mmap_write_lock holder is done with all modifications and drops mmap_lock, > > it will increment mm->lock_seq, effectively unlocking all VMAs marked as > > locked. > [...] > > +static inline void vma_read_unlock(struct vm_area_struct *vma) > > +{ > > + up_read(&vma->lock); > > +} > > One thing that might be gnarly here is that I think you might not be > allowed to use up_read() to fully release ownership of an object - > from what I remember, I think that up_read() (unlike something like > spin_unlock()) can access the lock object after it's already been > acquired by someone else. So if you want to protect against concurrent > deletion, this might have to be something like: > > rcu_read_lock(); /* keeps vma alive */ > up_read(&vma->lock); > rcu_read_unlock(); But for deleting VMA one would need to write-lock the vma->lock first, which I assume can't happen until this up_read() is complete. Is that assumption wrong? > > But I'm not entirely sure about that, the locking folks might know better. > > Also, it might not matter given that the rw_semaphore part is removed > in the current patch 41/41 anyway... This does matter because Michal suggested dropping that last 41/41 patch for now.