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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:

<snip>

How does your change interact with the recent "break up the binder big
lock" patchset:
https://android-review.googlesource.com/#/c/354698/

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

thanks,

greg k-h

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