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

[Joel E. Denny via llvm-dev]

Hi David, Chandler,

I see lldb tests hang often, and then I kill the dotest process.

I'd like to stop running check-all too, but I feel it's important when I
modify FileCheck.  The flakiness that Chandler mentioned makes it
time-consuming to verify test results.

Joel

On Wed, Jan 2, 2019 at 4:41 PM Chandler Carruth via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> 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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