From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1526365659; cv=none; d=google.com; s=arc-20160816; b=BO/LOA1r4D8Oz0T0nZxfRqtsxPp6XlondSO1DJ+eoQcZtBA8N+crORVn/kB3RLNhCj 26yAQWnBJPK9Qf+7aed67rHsBE+FE1isYO/CE7E9tN6hj3qKZUNM2zt5mUYmbi6FmC24 igXgpoPE2VxMPK8mO+YvV/rNYviT5dHqCQrZCRurIlH3z6MWzfRG6vs8kAvu98P29eQv ypLuXlcE6AL0pxrGbE4CviirWYZSaQVf63Ki+CQsb/JLusXvHDKrMZuhyxEoQnZjpZuH yAglyaNs3gs3yi2C9CbsCrSs6zPeLTbykOxg/5RQzO/kBMfjtHp0EgyVAvk1Xr57Wtqi yljA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-transfer-encoding :content-disposition:mime-version:references:message-id:subject:cc :to:date:from:dkim-signature:arc-authentication-results; bh=zphKUf2FW4RAln8KpU6kmkNfe+snNuhKFzd8FNUySWg=; b=Y2UhhahnnE0qRtEOMhBlHdcyHI8M+CNNXgZmFm/R00mf3lt5MmUoqcgS7NU6kbD3ft U9DiRBLfakJ/WBmiY3z6BFXScA7l1KRiv6NsLYiiQjA1HKadY5c5tLk+X+/xW1sDFPW1 sgqqo4JHWFMO23xmPH601PwoX03VtvjTTTp568JyQF3LEoyLyRFX38H4jfgTgTnc95Gx 5yfbGiCCHqxQ3l9N61Q1v5BQAdjPbPn6oHCbGFduxA9QH+36PASi+KfrwkFJaDdsptRc jHv0GAu2mLCZ1ev5G6d6ec/5zCmOOkNVQVxlZSXCxaTV0nwTtDHBhferJ9r9wDUmnOxu hfMA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=bb0T8/BY; spf=pass (google.com: domain of minchan.kernel@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=minchan.kernel@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=bb0T8/BY; spf=pass (google.com: domain of minchan.kernel@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=minchan.kernel@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com X-Google-Smtp-Source: AB8JxZoMOT0I1IumvA+jLO0zxp+cFvm/WJOBH0L7hG5aAYwsBTqDQ7DBl++W0NX/quNlJDJcq2A/Tw== From: Minchan Kim X-Google-Original-From: Minchan Kim Date: Tue, 15 May 2018 15:27:32 +0900 To: Joel Fernandes Cc: LKML , Ganesh Mahendran , Joe Perches , Arve =?iso-8859-1?B?SGr4bm5lduVn?= , Todd Kjos , Greg Kroah-Hartman , Martijn Coenen Subject: Re: [PATCH v6] ANDROID: binder: change down_write to down_read Message-ID: <20180515062732.GA183759@rodete-desktop-imager.corp.google.com> References: <20180507141537.4855-1-minchan@kernel.org> <20180507172829.GA66161@joelaf.mtv.corp.google.com> <20180508105101.GB8209@rodete-desktop-imager.corp.google.com> <20180508230813.GA102094@joelaf.mtv.corp.google.com> <20180509064023.GD8209@rodete-desktop-imager.corp.google.com> <20180509231941.GA4790@joelaf.mtv.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180509231941.GA4790@joelaf.mtv.corp.google.com> User-Agent: Mutt/1.9.2 (2017-12-15) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1599815073448562806?= X-GMAIL-MSGID: =?utf-8?q?1600510397863754496?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Hi Joel, Sorry for the late response. I was off. On Wed, May 09, 2018 at 04:19:41PM -0700, Joel Fernandes wrote: > On Wed, May 09, 2018 at 03:40:23PM +0900, Minchan Kim wrote: > > On Tue, May 08, 2018 at 04:08:13PM -0700, Joel Fernandes wrote: > > > On Tue, May 08, 2018 at 07:51:01PM +0900, Minchan Kim wrote: > > > > On Mon, May 07, 2018 at 10:28:29AM -0700, Joel Fernandes wrote: > > > > > On Mon, May 07, 2018 at 11:15:37PM +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 binder_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. > > > > > > Please use proper API down_read. It would help mmap_sem contention > > > > > > problem as well as fixing down_write abuse. > > > > > > > > > > > > Ganesh Mahendran tested app launching and binder throughput test > > > > > > and he said he couldn't find any problem and I did binder latency > > > > > > test per Greg KH request(Thanks Martijn to teach me how I can do) > > > > > > I cannot find any problem, too. > > > > > > > > > > > > Cc: Ganesh Mahendran > > > > > > Cc: Joe Perches > > > > > > Cc: Arve Hjønnevåg > > > > > > Cc: Todd Kjos > > > > > > Cc: Greg Kroah-Hartman > > > > > > Reviewed-by: Martijn Coenen > > > > > > Signed-off-by: Minchan Kim > > > > > > --- > > > > > > drivers/android/binder.c | 4 +++- > > > > > > drivers/android/binder_alloc.c | 6 +++--- > > > > > > 2 files changed, 6 insertions(+), 4 deletions(-) > > > > > > > > > > > > diff --git a/drivers/android/binder.c b/drivers/android/binder.c > > > > > > index 4eab5be3d00f..7b8e96f60719 100644 > > > > > > --- a/drivers/android/binder.c > > > > > > +++ b/drivers/android/binder.c > > > > > > @@ -4730,7 +4730,9 @@ 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; > > > > > > + vma->vm_flags &= ~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..4f382d51def1 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); > > > > > > > > > > > > > > > Nice. Is there a need to hold the reader-lock at all here? Just curious what > > > > > else is it protecting (here or in vm_insert_page). > > > > > > > > It should protect vm_area_struct. IOW, when we try insert page into virtual address area, > > > > vma shouldn't be changed(ie, unmap/collapse/split). > > > > > > When you say unmap, are you talking about pages being unmapped from the VMA > > > or something else? > > > > I mean to destroy vm_area_struct itself as well as unmap pages. > > > > > > > > For the collapse/split part, the binder VMA (vm_area_struct) itself isn't > > > changed after the initial mmap (AFAIK) so I don't see a need for protection > > > there. > > > > There is no way to unmap in runtime? What happens if some buggy applications > > do unmap by mistake? > > Cannot we access those B's vma from A context? > > If B process is exiting, the VMA would be gone while A is accessing. > > If the VMA is gone, then why is it a good idea to map pages into it anyway? Hmm, sorry about that. I couldn't understand your point. > > About the unmap at runtime part, your commit message was a bit confusing. You > said "every binder buffers should be mapped in advance by binder_mmap." but I > think the new binder shrinker mechanism doesn't make that true anymore. It's good point. I didn't know know that. When I see binder_vm_fault, it emits SIGBUS. That means shrinker cannot zap pages process is using, I think. IOW, every pages for binder are mapped at mmap time and is never mapped in runtime by page fault. Right? Thanks. > > The unmap by mistake point is a valid one I guess. > > thanks, > > - Joel >