From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 28 Mar 2018 07:53:54 +0200 From: Greg Kroah-Hartman To: Minchan Kim Cc: LKML , Martijn Coenen , Todd Kjos Subject: Re: [PATCH] ANDROID: binder: change down_write to down_read Message-ID: <20180328055354.GC6212@kroah.com> References: <20180328024231.239725-1-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180328024231.239725-1-minchan@kernel.org> User-Agent: Mutt/1.9.4 (2018-02-28) X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 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? thanks, greg k-h