From 720c241924046aff83f5f2323232f34a30a4c281 Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Mon, 7 May 2018 23:15:37 +0900 Subject: ANDROID: binder: change down_write to down_read MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Martijn Coenen Signed-off-by: Minchan Kim Reviewed-by: Joel Fernandes (Google) Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'drivers/android/binder.c') diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 9c30d38..e94e2b1 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -4727,7 +4727,9 @@ 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; -- cgit v1.1