UPSTREAM: ANDROID: binder: change down_write to down_read
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>
Reviewed-by: Martijn Coenen <maco@android.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 720c241924046aff83f5f2323232f34a30a4c281)
Change-Id: I8358ceaaab4030f7122c95308dcad59557cad411
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 6c646fd..bec6c0a 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -219,7 +219,7 @@
mm = alloc->vma_vm_mm;
if (mm) {
- down_write(&mm->mmap_sem);
+ down_read(&mm->mmap_sem);
vma = alloc->vma;
}
@@ -288,7 +288,7 @@
/* vm_insert_page does not seem to increment the refcount */
}
if (mm) {
- up_write(&mm->mmap_sem);
+ up_read(&mm->mmap_sem);
mmput(mm);
}
return 0;
@@ -321,7 +321,7 @@
}
err_no_vma:
if (mm) {
- up_write(&mm->mmap_sem);
+ up_read(&mm->mmap_sem);
mmput(mm);
}
return vma ? -ENOMEM : -ESRCH;