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From: Derrick Stolee <stolee@gmail.com>
To: Jeff King <peff@peff.net>
Cc: "SZEDER Gábor" <szeder.dev@gmail.com>,
	"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 10:27:16 -0400	[thread overview]
Message-ID: <131dfa37-0f65-f0c3-6f30-5b6eca12d9c0@gmail.com> (raw)
In-Reply-To: <20190829141307.GE1797@sigill.intra.peff.net>

On 8/29/2019 10:13 AM, Jeff King wrote:
> On Thu, Aug 29, 2019 at 08:58:55AM -0400, Derrick Stolee wrote:
> 
>> 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.
> 
> I don't think we should need such a call. For one thing, if it were
> necessary, that would mean we're not writing out the packet at all. But
> your whole problem is that we're writing the message twice, one of which
> comes from the packet.

The problem the flush() was trying to solve was the new "Broken pipe" error,
which I had assumed was due to a communication race. (Looking at the message
more closely now, I see that Szeder was able to repro this broken pipe both
with and without my change. I am still unable to repro the broken pipe.)

> Second is that this is not "flush the output stream", but "write a flush
> packet". The packet_writer_error() function immediately calls write()
> without buffering. And no matter where we are in the conversation, a
> flush packet would not be necessary, because the error packet we send
> would be interpreted immediately by the client as aborting the
> connection.

This clearly shows that my proposed solution is absolutely wrong.

Thanks,
-Stolee


  reply	other threads:[~2019-08-29 14:27 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
2019-08-29 14:13             ` Jeff King
2019-08-29 14:27               ` Derrick Stolee [this message]
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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