From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1522219635; cv=none; d=google.com; s=arc-20160816; b=MgWqOPZ+ZmU8Fsx80tp+XALvz4ddv0IbLeIsNJu9bJYIE+cfiINn3H8yh40dLB+2gi pB9NCo9a+C50rB9SRyrgtIGLRBUYbVLdcbbIM2iZZZY3YlPtNKyB40eBRIDBENe7+YKt Ly7TIHFlquDABYoxBP4yCyhcXfIpRF4pieCTvmP/Z49KqxXmtNCZMdSYHCgQjC27nS0A 8s1G0nej6Kn122IRlaj6fk8NTv8CbcVSHn0IzOCkfSbauTfrAvzRDXvkeDgA2LCh4e5s W8HbFxkuBIb7ZbPGLXZnfN/DhcAA819wylGbim5aRjenLa1+6ymWf91s9S1IMx3rQXvz CJ3w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:sender:dkim-signature :arc-authentication-results; bh=/fGuBi//+vPI3ZSMXSb/7cJRqEJsW1h7hvlWUlx532g=; b=hQIThMZTJxCIyR6MHZc0xBgC//aW0es4Ht4zQAapJUNuQPyCp48SNWE0mtkjURu56C DWQvTDV1XwMUs1Ukt6wBq2q01+d1oLCtDc57MdJlxO1fhZFfA0ojG3kHRJvNGpYn/Cjw PeKVFuA8NdR3O2KwA6ucC00GOwjKsdws8Y8OESpwfKcnc6A3LqEE4idBkcuCunArxNiS aiFzxN+CE/ZQEeU3JTHJR/vz3y+N1uOprJjNZnTxYztmQrd2COle/LGYKcPZV2rr9ADy /vqUabD4YPUuLgAL3o1Wxw5pK2/LiF3hQTfvg0bT6w203mhWb23qPLvgJ3DvWBN3PHNT +RqA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=Fkpzm3po; spf=pass (google.com: domain of minchan.kim@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=minchan.kim@gmail.com Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=Fkpzm3po; spf=pass (google.com: domain of minchan.kim@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=minchan.kim@gmail.com X-Google-Smtp-Source: AG47ELtoVaEiL3E3kDvJUZ4su4y6trMVZZ32SmaHYxSuAq0TbcNPGxMG8+ngxRhxGDnesU09fHsHSg== Sender: Minchan Kim Date: Wed, 28 Mar 2018 15:47:08 +0900 From: Minchan Kim To: Greg Kroah-Hartman Cc: LKML , Martijn Coenen , Todd Kjos Subject: Re: [PATCH] ANDROID: binder: change down_write to down_read Message-ID: <20180328064708.GA44818@rodete-desktop-imager.corp.google.com> References: <20180328024231.239725-1-minchan@kernel.org> <20180328055354.GC6212@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180328055354.GC6212@kroah.com> User-Agent: Mutt/1.9.2 (2017-12-15) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1596147613657109396?= X-GMAIL-MSGID: =?utf-8?q?1596162976376022446?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, Mar 28, 2018 at 07:53:54AM +0200, Greg Kroah-Hartman wrote: > On Wed, Mar 28, 2018 at 11:42:31AM +0900, Minchan Kim wrote: > > binder_update_page_range needs down_write of mmap_sem because > > vm_insert_page need to change vma->vm_flags to VM_MIXEDMAP unless > > it is set. However, when I profile binder working, it seems > > every binder buffers should be mapped in advance by binder_mmap. > > It means we could set VM_MIXEDMAP in bider_mmap time which is > > already hold a mmap_sem as down_write so binder_update_page_range > > doesn't need to hold a mmap_sem as down_write. > > > > Android suffers from mmap_sem contention so let's reduce mmap_sem > > down_write. > > > > Cc: Martijn Coenen > > Cc: Todd Kjos > > Cc: Greg Kroah-Hartman > > Signed-off-by: Minchan Kim > > --- > > drivers/android/binder.c | 2 +- > > drivers/android/binder_alloc.c | 8 +++++--- > > 2 files changed, 6 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/android/binder.c b/drivers/android/binder.c > > index 764b63a5aade..9a14c6dd60c4 100644 > > --- a/drivers/android/binder.c > > +++ b/drivers/android/binder.c > > @@ -4722,7 +4722,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma) > > failure_string = "bad vm_flags"; > > goto err_bad_arg; > > } > > - vma->vm_flags = (vma->vm_flags | VM_DONTCOPY) & ~VM_MAYWRITE; > > + vma->vm_flags |= (VM_DONTCOPY | VM_MIXEDMAP) & ~VM_MAYWRITE; > > vma->vm_ops = &binder_vm_ops; > > vma->vm_private_data = proc; > > > > diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c > > index 5a426c877dfb..a184bf12eb15 100644 > > --- a/drivers/android/binder_alloc.c > > +++ b/drivers/android/binder_alloc.c > > @@ -219,7 +219,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate, > > mm = alloc->vma_vm_mm; > > > > if (mm) { > > - down_write(&mm->mmap_sem); > > + down_read(&mm->mmap_sem); > > vma = alloc->vma; > > } > > > > @@ -229,6 +229,8 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate, > > goto err_no_vma; > > } > > > > + WARN_ON_ONCE(vma && !(vma->vm_flags & VM_MIXEDMAP)); > > What can we do with this warning? What about systems that run in 'panic > on warn' mode? Is this something we should handle directly instead? Hmm, it seems we don't need above warning there because vm_insert_page will hit BUG_ON in that case. I will remove it at respin. Thanks for the review, Greg. I will wait other binder maintainer's opinion about below question. > > it seems > > every binder buffers should be mapped in advance by binder_mmap.