config: android-recommended: disable aio support

The aio interface adds substantial attack surface for a feature that's
not being exposed by Android at all.  It's unlikely that anyone is using
the kernel feature directly either.  This feature is rarely used even on
servers.  The glibc POSIX aio calls really use thread pools.  The lack
of widespread usage also means this is relatively poorly audited/tested.

The kernel's aio rarely provides performance benefits over using a
thread pool and is quite incomplete in terms of system call coverage
along with having edge cases where blocking can occur.  Part of the
performance issue is the fact that it only supports direct io, not
buffered io.  The existing API is considered fundamentally flawed and
it's unlikely it will be expanded, but rather replaced:

  https://marc.info/?l=linux-aio&m=145255815216051&w=2

Since ext4 encryption means no direct io support, kernel aio isn't even
going to work properly on Android devices using file-based encryption.

Reviewed-at: https://android-review.googlesource.com/#/c/292158/

Link: http://lkml.kernel.org/r/1481113148-29204-1-git-send-email-amit.pundir@linaro.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Cc: Rob Herring <rob.herring@linaro.org>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/configs/android-recommended.config

@@ -1,4 +1,5 @@
 #  KEEP ALPHABETICALLY SORTED
+# CONFIG_AIO is not set
 # CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set
 # CONFIG_INPUT_MOUSE is not set
 # CONFIG_LEGACY_PTYS is not set