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charset="UTF-8" X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4F269180004 X-Rspam-User: X-Stat-Signature: 433zuoqwnq8y4p77frix3mt1ozt7zfhz X-HE-Tag: 1673987802-147149 X-HE-Meta: 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 LvfGYMFV zdTotBLwrTsrae4I= 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 8:51 PM Jann Horn wrote: > On Mon, Jan 9, 2023 at 9:55 PM Suren Baghdasaryan wrote: > > Due to the possibility of handle_userfault dropping mmap_lock, avoid fault > > handling under VMA lock and retry holding mmap_lock. This can be handled > > more gracefully in the future. > > > > Signed-off-by: Suren Baghdasaryan > > Suggested-by: Peter Xu > > --- > > mm/memory.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/mm/memory.c b/mm/memory.c > > index 20806bc8b4eb..12508f4d845a 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -5273,6 +5273,13 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, > > if (!vma->anon_vma) > > goto inval; > > > > + /* > > + * Due to the possibility of userfault handler dropping mmap_lock, avoid > > + * it for now and fall back to page fault handling under mmap_lock. > > + */ > > + if (userfaultfd_armed(vma)) > > + goto inval; > > This looks racy wrt concurrent userfaultfd_register(). I think you'll > want to do the userfaultfd_armed(vma) check _after_ locking the VMA, I still think this change is needed... > and ensure that the userfaultfd code write-locks the VMA before > changing the __VM_UFFD_FLAGS in vma->vm_flags. Ah, but now I see you already took care of this half of the issue with the reset_vm_flags() change in https://lore.kernel.org/linux-mm/20230109205336.3665937-16-surenb@google.com/ . > > if (!vma_read_trylock(vma)) > > goto inval; > > > > -- > > 2.39.0 > >