[PATCH] MIPS: run tst-mode-switch-{1,2,3}.c using test-skeleton.c

[Maciej W. Rozycki]

On Mon, 27 Jun 2016, Aurelien Jarno wrote:

> For some reasons I have not investigated yet, tst-mode-switch-1 hangs on
> a MIPS UTM-8 machine running an o32 userland and a 3.6.1 kernel.
> 
> This patch changes the test so that it runs under the test-skeleton
> framework, causing the test to fail after a timeout instead of hanging
> the whole testsuite. At the same time, also change the tst-mode-switch-2
> and tst-mode-switch-3 tests.

 FWIW I've noticed that too, with o32 and Linux 4.6.0-rc7.  As I found the 
hang quite annoying I made and have been using a similar change locally, 
albeit to `tst-mode-switch-1' only, which I didn't get to submitting as I 
got distracted with other stuff.

 Interestingly enough the lone switch to running under the skeleton made 
the hang go away for me entirely -- the test started succeeding rather 
than hitting the skeleton's timeout.  So I guess there's a race somewhere 
leading to a deadlock or suchlike, and by hiding the failure this way we 
may be making it more difficult to notice, let alone encourage someone to 
actually fix it.

 This was on an UP machine BTW, so the recent fix to prctl(2) (Linux 
commit 6b8322576e9d ("MIPS: Force CPUs to lose FP context during mode 
switches")) to use an IPI on MP configurations isn't supposed to apply. 
I've tried running the test case both without and with the fix applied 
anyway, just to make sure it indeed does not change anything, and -- as 
expected -- there was no change whatsoever.

  Maciej