[llvm-dev] [lit] check-all hanging

[Chandler Carruth via llvm-dev]

What you're seeing is just the fact that lit is waiting on subprocesses
(select is waiting on the pipes i suspect).

Anyways, you'll need to dig into what it is waiting on, and what *that*
process is doing that is stuck to make progress.

I've not seen anything like this, but I basically never run `check-all`
these days because LLDB and sanitizer tests are too flaky. =[ I've not been
able to interest anyone in fixing this either sadly.

On Wed, Jan 2, 2019 at 10:09 AM David Greene via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi,
>
> From time to time, I see check-all hang during running of lit tests.
> The hang always happens at the > 90% completion stage and I'm pretty
> sure all tests have been run and check-all is just waiting for
> lit/python to exit.  I see a single python processing running, taking
> very little CPU time.  An strace of that process shows this:
>
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 32168}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 1000})  = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 2000})  = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 4000})  = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 8000})  = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 16000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 32000}) = 0 (Timeout)
> futex(0x3bcc8c0, FUTEX_WAKE_PRIVATE, 1) = 1
> futex(0x3bcc8c0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL,
> ffffffff) = 0
> futex(0x3bcc8c0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL,
> ffffffff) = -1 EAGAIN (Resourc
> e temporarily unavailable)
>
> futex(0x3bcc8c0, FUTEX_WAKE_PRIVATE, 1) = 1
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> futex(0x3bcc8c0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL,
> ffffffff) = -1 EAGAIN (Resourc
> e temporarily unavailable)
>
> futex(0x3bcc8c0, FUTEX_WAKE_PRIVATE, 1) = 1
> futex(0x3bcc8c0, FUTEX_WAKE_PRIVATE, 1) = 1
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
> select(0, NULL, NULL, NULL, {0, 50000}) = 0 (Timeout)
>
> It appears that python is waiting for some I/O or something which never
> appears.
>
> Has anyone else seen this before?  Any ideas of what is going on or how
> to fix it?
>
>                               -David
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