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dkim=pass header.d=fb.com header.s=facebook header.b=hQH0HDyH; dmarc=pass (policy=reject) header.from=fb.com; spf=pass (imf16.hostedemail.com: domain of "prvs=8885b17d91=yhs@fb.com" designates 67.231.145.42 as permitted sender) smtp.mailfrom="prvs=8885b17d91=yhs@fb.com" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A8291F000090 X-HE-Tag: 1631128337-59014 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 9/8/21 11:49 AM, Jason Gunthorpe wrote: > On Wed, Sep 08, 2021 at 06:30:52PM +0000, Liam Howlett wrote: > >> /* Look up the first VMA which satisfies addr < vm_end, NULL if none. */ >> -struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) >> +struct vm_area_struct *find_vma_non_owner(struct mm_struct *mm, >> + unsigned long addr) >> { >> struct rb_node *rb_node; >> struct vm_area_struct *vma; >> >> - mmap_assert_locked(mm); >> + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); >> /* Check the cache first. */ >> vma = vmacache_find(mm, addr); >> if (likely(vma)) >> @@ -2325,6 +2326,11 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) >> return vma; >> } >> >> +struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) >> +{ >> + lockdep_assert_held(&mm->mmap_lock); >> + return find_vma_non_owner(mm, addr); >> +} >> EXPORT_SYMBOL(find_vma); >> >> /* >> >> >> Although this leaks more into the mm API and was referred to as ugly >> previously, it does provide a working solution and still maintains the >> same level of checking. > > I think it is no better than before. > > The solution must be to not break lockdep in the BPF side. If Peter's > reworked algorithm is not OK then BPF should drop/acquire the lockdep > when it punts the unlock to the WQ. The current warning is triggered by bpf calling find_vma(). Is it too late even if bpf does drop/acquire the lockdep when it punts the unlock to the WQ with irq_work_queue()? Maybe I missed something, could you be more specific about your proposed solution? > > 'non-owner' is just a nice way of saying 'the caller is messing with > lockdep', it is not a sane way to design APIs > > Jason >