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List:       coreutils
Subject:    Re: [PATCH] tests: fix races wrt output files of background processes
From:       Bernhard Voelker <mail () bernhard-voelker ! de>
Date:       2016-01-10 12:56:53
Message-ID: 56925515.9050800 () bernhard-voelker ! de
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On 01/10/2016 01:28 PM, Pádraig Brady wrote:
> On 10/01/16 00:56, Bernhard Voelker wrote:
>> At least the false positive in tail-2/follow-stdin.sh could be seen
>> on a 4-core i5 system with -j8.  Fix similar cases. too.
>>
>> * tests/tail-2/follow-stdin.sh: Empty the 'out' file in each iteration.
>> Otherwise, under heavy system load, 'check_tail_output' would see the
>> expected output from the previous round before tail would have the
>> chance to come up in the background.
> 
> Nice. Yes the fork (clone) happens before the open (O_TRUNC):
>   strace -f sh -c '/bin/true > out & pid=$!'
> 
>> * tests/dd/stats.sh: Likewise
>> * tests/misc/cat-buf.sh: Likewise.
>> * tests/misc/stdbuf.sh: Likewise.
> 
> No race for these 3 due to explicit `wait`,
> but better to make the change for consistency.
> 
>> * tests/tail-2/wait.sh
> 
> Yes this was racy too.

I also checked other places found by
   git grep -C20 '>.* & pid=' -- tests
but most of them don't use a loop or otherwise don't use the same output
file in consecutive test statements.  So I hope we got them all now.

> +1 to complete patch.

Thanks for the review - pushed.

Have a nice day,
Berny


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