Subject: Re: [PATCH 1/1] upload-pack: fix race condition in error messages

From: SZEDER Gábor <[email-masked]>
Date: Fri, 30 Aug 2019 00:06:30 +0200

On Thu, Aug 29, 2019 at 11:58:18PM +0200, SZEDER Gábor wrote:
> On Thu, Aug 29, 2019 at 10:38:05AM -0400, Jeff King wrote:
> > So any fixes there have to happen on the client side. I am still
> > confused about why the client is writing in this case, per the argument
> > in 014ade7484 (upload-pack: send ERR packet for non-tip objects,
> > 2019-04-13). It would be nice to use GIT_TRACE_PACKET to see what it's
> > trying to write, but I still haven't been able to reproduce the issue.
> 
> It's the "done" line:
> 
>   + cat trace-packet
>   packet:  upload-pack> 5e26403b4485d7a44fd8b65dc3f71e21c0dd6fad HEAD\0multi_ack thin-pack side-band side-band-64k ofs-delta shallow deepen-since deepen-not deepen-relative no-progress include-tag multi_ack_detailed allow-tip-sha1-in-want allow-reachable-sha1-in-want symref=HEAD:refs/heads/master agent=git/2.23.0.40.g4d780d4382.dirty
>   packet:  upload-pack> 5e26403b4485d7a44fd8b65dc3f71e21c0dd6fad refs/heads/master
>   packet:  upload-pack> 0000
>   packet:        fetch< 5e26403b4485d7a44fd8b65dc3f71e21c0dd6fad HEAD\0multi_ack thin-pack side-band side-band-64k ofs-delta shallow deepen-since deepen-not deepen-relative no-progress include-tag multi_ack_detailed allow-tip-sha1-in-want allow-reachable-sha1-in-want symref=HEAD:refs/heads/master agent=git/2.23.0.40.g4d780d4382.dirty
>   packet:        fetch< 5e26403b4485d7a44fd8b65dc3f71e21c0dd6fad refs/heads/master
>   packet:        fetch< 0000
>   packet:        fetch> want 64ea4c133d59fa98e86a771eda009872d6ab2886 multi_ack_detailed side-band-64k thin-pack no-progress ofs-delta deepen-since deepen-not agent=git/2.23.0.40.g4d780d4382.dirty
>   packet:        fetch> 0000
>   packet:  upload-pack< want 64ea4c133d59fa98e86a771eda009872d6ab2886 multi_ack_detailed side-band-64k thin-pack no-progress ofs-delta deepen-since deepen-not agent=git/2.23.0.40.g4d780d4382.dirty
>   packet:  upload-pack< 0000
>   packet:  upload-pack> ERR upload-pack: not our ref 64ea4c133d59fa98e86a771eda009872d6ab2886
>   packet:  upload-pack> 0000
>   packet:        fetch> done
> 
> In the avarage successful run that "fetch> done" pkt-line is
> immediately after the "fetch> 0000".
> 
> The above is on my Linux box; here is a failure on macOS, essentially
> the same:
> 
>   https://travis-ci.org/szeder/git/jobs/578555606#L3453
> 

Try this patch to reliably reproduce this failure:

diff --git a/fetch-pack.c b/fetch-pack.c
index 65be043f2a..e18864458b 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -471,6 +471,7 @@ static int find_common(struct fetch_negotiator *negotiator,
 	}
 done:
 	if (!got_ready || !no_done) {
+		sleep(1);
 		packet_buf_write(&req_buf, "done\n");
 		send_request(args, fd[1], &req_buf);
 	}
diff --git a/t/t5516-fetch-push.sh b/t/t5516-fetch-push.sh
index c81ca360ac..ebecc81c89 100755
--- a/t/t5516-fetch-push.sh
+++ b/t/t5516-fetch-push.sh
@@ -1252,7 +1252,9 @@ do
 			git fetch ../testrepo/.git $SHA1_2 &&
 			git cat-file commit $SHA1_2 &&
 			test_must_fail env GIT_TEST_PROTOCOL_VERSION= \
+				GIT_TRACE_PACKET="$(pwd)/trace-packet" \
 				git fetch ../testrepo/.git $SHA1_3 2>err &&
+			cat trace-packet &&
 			test_i18ngrep "remote error:.*not our ref.*$SHA1_3\$" err
 		)
 	'