From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1525714111; cv=none; d=google.com; s=arc-20160816; b=iW/ITyfm+Op+HyJgRpDB4mqytTat2gqP/MhjqwaQIDcsYlEBOWyeT6r2yKxhSVWzFo tmCQhw8u76lGDaLx0YbIwlVDr8GjpcPQ5oTv7xkRyGzi1tsz2fYPRFKS0mHPnVQGIDey NgRg2nxIll9AC2qcZ/ETa0JjqjEF6tq25EnRzdEDymmvqAjp+nG4WP1OVLU16eQS6rpN m4qaKWTRl23xWpMB8BhvgYrinrsebbqwYUiavLcdGYYeaEW/0agJ/viubWadTObN6a4k 5IBBzKeknrnfwoTf3LNmKwDEBbmxqV6T4d8DNcNZ3jiAglAnwFuDPA/IGDRA9Gk+l6au gBww== 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:from:date:dkim-signature:arc-authentication-results; bh=Y41PRU7Q9HRGUiur9BnwHZ6cqOn3i+qi5Fj72ftjwFU=; b=CV/mRVNGkn1A8LOkbXvSWbwrAOgy+IwepSE5ePf2CjdLu6dgkRnKWIjOop4g/sJM0T mTT6bOcNtJZQKeGJ2f3MH9oVhsOE9L/nk9he2wunM21kUh95J3Cwha52CbSKRLUxNlrJ mO4J9v5FxnrQY1XOIZobZ8K4u6XN9vRISywRMQsY4/cRvnKDcUYQIw5hrexe7Ac3x2dE HVtdWmagDTueeM2HjYRkSNhjs9qgL9Cj5P5SUdb/ge7n+to1EjZCjDlGOoz1kyXih+5t 3EU8Jl9yT2leYWJNiD8wv8wUcIMSxT6zHZCSGNEs8rrrh9qBJKrE6RKHbKjzhw0smFeG 0DJw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@joelfernandes-org.20150623.gappssmtp.com header.s=20150623 header.b=eIj4h7l2; spf=neutral (google.com: 209.85.220.65 is neither permitted nor denied by best guess record for domain of joel@joelfernandes.org) smtp.mailfrom=joel@joelfernandes.org Authentication-Results: mx.google.com; dkim=pass header.i=@joelfernandes-org.20150623.gappssmtp.com header.s=20150623 header.b=eIj4h7l2; spf=neutral (google.com: 209.85.220.65 is neither permitted nor denied by best guess record for domain of joel@joelfernandes.org) smtp.mailfrom=joel@joelfernandes.org X-Google-Smtp-Source: AB8JxZrAh64C5SZLfbc+LckXA6W6RWO2x4Nn/CJWjCFmuYielsJFC/YMphG2BZSyHHgVcVXX9d7LAQ== Date: Mon, 7 May 2018 10:28:29 -0700 From: Joel Fernandes To: Minchan Kim 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: <20180507172829.GA66161@joelaf.mtv.corp.google.com> References: <20180507141537.4855-1-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180507141537.4855-1-minchan@kernel.org> 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?1599827199854038577?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 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). Otherwise looks good to me: Reviewed-by: Joel Fernandes (Google) thanks, - Joel