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Wed, 14 Aug 2019 15:41:07 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.136]) by smtp.corp.redhat.com (Postfix) with SMTP id 504554CE; Wed, 14 Aug 2019 15:41:03 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 14 Aug 2019 17:41:06 +0200 (CEST) Date: Wed, 14 Aug 2019 17:41:02 +0200 From: Oleg Nesterov To: Kefeng Wang Cc: Michal Hocko , linux-mm , Andrea Arcangeli , Peter Xu , Mike Rapoport , Jann Horn , Jason Gunthorpe , Andrew Morton Subject: Re: [BUG] kernel BUG at fs/userfaultfd.c:385 after 04f5866e41fb Message-ID: <20190814154101.GF11595@redhat.com> References: <20190814135351.GY17933@dhcp22.suse.cz> <7e0e4254-17f4-5f07-e9af-097c4162041a@huawei.com> <20190814151049.GD11595@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190814151049.GD11595@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Wed, 14 Aug 2019 15:41:07 +0000 (UTC) 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 08/14, Oleg Nesterov wrote: > > On 08/14, Kefeng Wang wrote: > > > > On 2019/8/14 21:53, Michal Hocko wrote: > > > On Tue 13-08-19 17:08:05, Kefeng Wang wrote: > > >> > > >> Syzkaller reproducer: > > >> # {Threaded:true Collide:true Repeat:false RepeatTimes:0 Procs:1 Sandbox:none Fault:false FaultCall:-1 FaultNth:0 EnableTun:true EnableNetDev:true EnableNetReset:false EnableCgroups:false EnableBinfmtMisc:true EnableCloseFds:true UseTmpDir:true HandleSegv:true Repro:false Trace:false} > > >> r0 = userfaultfd(0x80800) > > >> ioctl$UFFDIO_API(r0, 0xc018aa3f, &(0x7f0000000200)) > > >> ioctl$UFFDIO_REGISTER(r0, 0xc020aa00, &(0x7f0000000080)={{&(0x7f0000ff2000/0xe000)=nil, 0xe000}, 0x1}) > > >> ioctl$UFFDIO_COPY(r0, 0xc028aa03, 0x0) > > >> ioctl$UFFDIO_COPY(r0, 0xc028aa03, &(0x7f0000000000)={&(0x7f0000ffc000/0x3000)=nil, &(0x7f0000ffd000/0x2000)=nil, 0x3000}) > > >> syz_execute_func(&(0x7f00000000c0)="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") > > >> poll(&(0x7f00000000c0)=[{}], 0x1, 0x0) > > > > > > Is there any way to decypher the above? > > > > no, I also want to know the way :( > > perhaps you can run it under strace? > > I am wondering if "goto skip_mm" in userfaultfd_release() is correct... > shouldn't it clear VM_UFFD_* and reset vm_userfaultfd_ctx.ctx even if > !mmget_still_valid ? Heh, I didn't notice you too mentioned userfaultfd_release() in your email. can you try the patch below? Oleg. --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -880,6 +880,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file) /* len == 0 means wake all */ struct userfaultfd_wake_range range = { .len = 0, }; unsigned long new_flags; + bool xxx; WRITE_ONCE(ctx->released, true); @@ -895,8 +896,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file) * taking the mmap_sem for writing. */ down_write(&mm->mmap_sem); - if (!mmget_still_valid(mm)) - goto skip_mm; + xxx = mmget_still_valid(mm); prev = NULL; for (vma = mm->mmap; vma; vma = vma->vm_next) { cond_resched(); @@ -907,19 +907,20 @@ static int userfaultfd_release(struct inode *inode, struct file *file) continue; } new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); - prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, - new_flags, vma->anon_vma, - vma->vm_file, vma->vm_pgoff, - vma_policy(vma), - NULL_VM_UFFD_CTX); - if (prev) - vma = prev; - else - prev = vma; + if (xxx) { + prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, + new_flags, vma->anon_vma, + vma->vm_file, vma->vm_pgoff, + vma_policy(vma), + NULL_VM_UFFD_CTX); + if (prev) + vma = prev; + else + prev = vma; + } vma->vm_flags = new_flags; vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; } -skip_mm: up_write(&mm->mmap_sem); mmput(mm); wakeup: