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Re: [PATCH] nptl: Fix racy pipe closing in tst-cancel{20,21}
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: "Paul E. Murphy" <murphyp at linux dot vnet dot ibm dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Mon, 9 Nov 2015 10:21:16 -0200
- Subject: Re: [PATCH] nptl: Fix racy pipe closing in tst-cancel{20,21}
- Authentication-results: sourceware.org; auth=none
- References: <1444849395-18800-1-git-send-email-adhemerval dot zanella at linaro dot com> <20151014195832 dot GY8645 at brightrain dot aerifal dot cx> <56253E21 dot 5000403 at linaro dot org> <5632572B dot 7030101 at linaro dot org> <56327A8D dot 7020307 at linux dot vnet dot ibm dot com>
Thanks for checking this out. Anyone more have any more comments on that?
On 29-10-2015 17:59, Paul E. Murphy wrote:
> This looks ok to me. Failing with a timeout seems better than
> incorrectly reporting a pass. Though, a 40 second timeout seems
> a bit high to me.
>
> Tested on ppc64.
>
> Paul
>
> On 10/29/2015 12:28 PM, Adhemerval Zanella wrote:
>> Ping.
>>
>> On 19-10-2015 17:01, Adhemerval Zanella wrote:
>>> Ping.
>>>
>>> On 14-10-2015 16:58, Rich Felker wrote:
>>>> On Wed, Oct 14, 2015 at 04:03:15PM -0300, Adhemerval Zanella wrote:
>>>>> The tst-cancel20 open two pipes and creates a thread which blocks
>>>>> reading the first pipe. It then issues a signal to activate an
>>>>> handler which also blocks reading the second pipe. Finally the
>>>>> cancellation cleanup-up handlers are tested by first closing the
>>>>> all the pipe ends and issuing a pthread_cancel. The tst-cancel21
>>>>> have a similar behavior, but use an extra fork after the test itself.
>>>>>
>>>>> The race condition occurs if the cancellation handling acts after the
>>>>> pipe close: in this case read will return EOF (indicating side-effects)
>>>>> and thus the cancellation must not act. However current GLIBC
>>>>> cancellation behavior acts regardless the syscalls returns with
>>>>> sid-effects.
>>>>>
>>>>> This patch adjust the test by moving the pipe closing after the
>>>>> cancellation handling. This avoid spurious cancellation for the
>>>>> case described.
>>>>>
>>>>> Checked on x86_64 and i386.
>>>>
>>>> I was involved in the discussion of this and believe that the fix is
>>>> correct. The only reason the tests "worked" before was that
>>>> cancellation was wrongly being acted upon after read succeeded in
>>>> reading EOF.
>>>>
>>>> Note that, with this change, the tests will now timeout if read fails
>>>> to act on cancellation, rather than exiting with a reportable error.
>>>> This could be fixed with some very complicated machinery involving an
>>>> additional signal handler and AS-safe synchronization mechanisms to
>>>> control the ordering of close with respect to interruption of read,
>>>> but as long as timeout is an acceptable way of detecting test failure,
>>>> I see no reason to complicate the test logic like that.
>>>>
>>>> Rich
>>>>
>>
>