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From: Derrick Stolee <stolee@gmail.com>
To: "SZEDER Gábor" <szeder.dev@gmail.com>, "Jeff King" <peff@peff.net>
Cc: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>,
	git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
	Derrick Stolee <dstolee@microsoft.com>
Subject: Re: [PATCH 1/1] upload-pack: fix race condition in error messages
Date: Thu, 29 Aug 2019 08:58:55 -0400	[thread overview]
Message-ID: <4d5773f9-4637-d8a3-d683-82624950f319@gmail.com> (raw)
In-Reply-To: <20190828161552.GE8571@szeder.dev>

On 8/28/2019 12:15 PM, SZEDER Gábor wrote:
> On Wed, Aug 28, 2019 at 11:39:44AM -0400, Jeff King wrote:
>> On Wed, Aug 28, 2019 at 10:54:12AM -0400, Jeff King wrote:
>>
>>>> Unfortunately, however, while running './t5516-fetch-push.sh -r 1,79
>>>> --stress' to try to reproduce a failure caused by those mingled
>>>> messages, the same check only failed for a different reason so far
>>>> (both on Linux and macOS (on Travis CI)):
>>>
>>> There's some hand-waving argument that this should be race-free in
>>> 014ade7484 (upload-pack: send ERR packet for non-tip objects,
>>> 2019-04-13), but I am not too surprised if there is a flaw in that
>>> logic.
>>
>> By the way, I've not been able to reproduce this locally after ~10
>> minutes of running "./t5516-fetch-push.sh -r 1,79 --stress" on my Linux
>> box. I wonder what's different.
>>
>> Are you running the tip of master?
> 
> Yeah, but this seems to be one of those "you have to be really lucky,
> even with --stress" cases.
> 
> So...  I was away for keyboard for over an hour and let it run on
> 'master', but it didn't fail.  Then I figured that I give it a try
> with Derrick's patch, because, well, why not, and then I got this
> broken pipe error in ~150 repetitions.  Run it again, same error after
> ~200 reps.  However, I didn't understand how that patch could lead to
> broken pipe, so went back to stressing master...  nothing.  So I
> started writing the reply to that patch saying that it seems to cause
> some racy failures on Linux, and was already proofreading before
> sending when the damn thing finally did fail.  Oh, well.
> 
> Then tried it on macOS, and it failed fairly quickly.  For lack of
> better options I used Travis CI's debug shell to access a mac VM, and
> could reproduce the failure both with and without the patch before it
> timeouted.

I'm running these tests under --stress now, but not seeing the error
you saw.

However, I do have a theory: the process exits before flushing the
packet line. Adding this line before exit(1) should fix it:

	packet_writer_flush(writer);

I can send this in a v2, but it would be nice if you could test this
in your environment that already demonstrated the failure.

Thanks,
-Stolee


  reply	other threads:[~2019-08-29 12:58 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-28  1:43 [PATCH 0/1] upload-pack: fix race condition in t5516 Derrick Stolee via GitGitGadget
2019-08-28  1:43 ` [PATCH 1/1] upload-pack: fix race condition in error messages Derrick Stolee via GitGitGadget
2019-08-28  9:34   ` SZEDER Gábor
2019-08-28 14:54     ` Jeff King
2019-08-28 15:39       ` Jeff King
2019-08-28 16:15         ` SZEDER Gábor
2019-08-29 12:58           ` Derrick Stolee [this message]
2019-08-29 14:13             ` Jeff King
2019-08-29 14:27               ` Derrick Stolee
2019-08-29 14:38                 ` Jeff King
2019-08-29 21:58                   ` SZEDER Gábor
2019-08-29 22:06                     ` SZEDER Gábor
2019-08-30 12:10                       ` SZEDER Gábor
2019-09-04  5:04                         ` Jeff King
2019-09-10 12:08                           ` SZEDER Gábor

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