[lkml]   [2017]   [Mar]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC PATCH] binder: Don't require the binder lock when killed in binder_thread_read()
On Fri, Mar 31, 2017 at 10:53:41AM -0700, Douglas Anderson wrote:
> Sometimes when we're out of memory the OOM killer decides to kill a
> process that's in binder_thread_read(). If we happen to be waiting
> for work we'll get the kill signal and wake up. That's good. ...but
> then we try to grab the binder lock before we return. That's bad.
> The problem is that someone else might be holding the one true global
> binder lock. If that one other process is blocked then we can't
> finish exiting. In the worst case, the other process might be blocked
> waiting for memory. In that case we'll have a really hard time
> exiting.
> On older kernels that don't have the OOM reaper (or something
> similar), like kernel 4.4, this is a really big problem and we end up
> with a simple deadlock because:
> * Once we pick a process to OOM kill we won't pick another--we first
> wait for the process we picked to die. The reasoning is that we've
> given the doomed process access to special memory pools so it can
> quit quickly and we don't have special pool memory to go around.
> * We don't have any type of "special access donation" that would give
> the mutex holder our special access.
> On kernel 4.4 w/ binder patches, we easily see this happen:


How does your change interact with the recent "break up the binder big
lock" patchset:

Have you tried that series out to see if it helps out any?


greg k-h

 \ /
  Last update: 2017-03-31 21:31    [W:0.064 / U:1.524 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site