From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1525820895; cv=none; d=google.com; s=arc-20160816; b=mmyaBJv1DdMcYk29wPt4Y05n4E6z/jW3er6iyBOOfrAIDCYJPpBpNmnc5PZNlrY5l9 vC59jhPaJDbj1grqXpxWxLphdpoEB/fXh7p3JSoYcc8bTR8SIZQZF5P/VByDoqf0mqLM YeBJLeVn1Nhboca0M0QMBV9fgQhH6ZFpUOrDZ508LacMB2ywXtGiRVQlmBNOJ9Vdt9C7 HTjWk/rtiNGcr4BYWE3Dv5l/32I3tpdl62J12hWuKU5IlYiOzbQWz+I9nrGwKPbQXS/W +diRjk34HbvDx9FJFbYyNdju/dBcDDDyq6576N/TSuAR52heYNeBG4h97sp4fu8Kusdu Ogmw== 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=4e1m7bEZTdWTIwkFukaR2xOJrWi3dJevGbhj+sWS/QM=; b=xVckuNa4NBttDqkxVOfg08MDAF3lBQgw0cq+Bi+7olu0O+74rvr8YAFgNGtyFL8wO6 0Ce5UVNK8GNK791XkNCdgUaLOxHd8zms0/cLFxhqsGxBEd3U4MSBYJ9C3tWvGEJYaDk/ wOGcsblaY9v4H62wIq9J7D9tx5kOVejAbZK4oFC4sjh8pwdsVZkma7Ffbg83UWe9nu62 cfKAiva3ZsvkCjotrODCRnTmwoCWFPb9bLR9TyIJ+/nWl4ZTCnzULfPJ5ZNLs8mSsRzi 6yUZkCvT5QfvIidagxd6hbEXiDfgv1UoniTlV1TJbN9IYW1V0rRO1kKQvLsVjxZi1uiU gADA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@joelfernandes-org.20150623.gappssmtp.com header.s=20150623 header.b=uuQhuKVi; 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=uuQhuKVi; 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: AB8JxZqKha2myqJXkmXf7MO3I0Zspyi8W2jtg1Qd+Jwxr1e0fEd56ZFWocMiPubeuidKVj2WcqWLCg== Date: Tue, 8 May 2018 16:08:13 -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: <20180508230813.GA102094@joelaf.mtv.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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180508105101.GB8209@rodete-desktop-imager.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?1599939171157420358?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 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? 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. Again, I'm not against the patch but thought its good to clarify for myself what the usage of the lock is, here. thanks, - Joel