Messages in this thread | | | Date | Mon, 7 May 2018 10:28:29 -0700 | From | Joel Fernandes <> | Subject | Re: [PATCH v6] ANDROID: binder: change down_write to down_read |
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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 <opensource.ganesh@gmail.com> > Cc: Joe Perches <joe@perches.com> > Cc: Arve Hjønnevåg <arve@android.com> > Cc: Todd Kjos <tkjos@google.com> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Reviewed-by: Martijn Coenen <maco@android.com> > Signed-off-by: Minchan Kim <minchan@kernel.org> > --- > 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) <joel@joelfernandes.org>
thanks,
- Joel
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