Re: Bug report: Git pull hang occasionally
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Dec 21, 2016, 21:32 UTC
- Message-ID
- <xmqqshphge7o.fsf@gitster.mtv.corp.google.com>
- In-Reply-To
- <xmqq8tr9huc0.fsf@gitster.mtv.corp.google.com>
Junio C Hamano <gitster@pobox.com> writes:
Show 17 quoted lines
> And the unexpected discrepancy is reported by find_symref() as > fatal. The server side dies, and somehow that fact is lost between > the upload-pack process and the client and somebody in the middle > (e.g. fastcgi interface or nginx webserver on the server side, or > the remote-curl helper on the client side) keeps the "git fetch" > process waiting. > > So there seem to be two issues. > > - Because of the unlocked read, find_symref() can observe an > inconsistent state. Perhaps it should be updated not to die but > to retry, expecting that transient inconsistency will go away. > > - A fatal error in upload-pack is not reported back to the client > to cause it exit is an obvious one, and even if we find a way to > make this fatal error in find_symref() not to trigger, fatal > errors in other places in the code can trigger the same symptom.
I wonder if the latter is solved by recent patch 296b847c0d ("remote-curl: don't hang when a server dies before any output", 2016-11-18) on the client side.
-- >8 -- From: David Turner <dturner@twosigma.com> Date: Fri, 18 Nov 2016 15:30:49 -0500 Subject: [PATCH] remote-curl: don't hang when a server dies before any output
In the event that a HTTP server closes the connection after giving a 200 but before giving any packets, we don't want to hang forever waiting for a response that will never come. Instead, we should die immediately.
One case where this happens is when attempting to fetch a dangling object by its object name. In this case, the server dies before sending any data. Prior to this patch, fetch-pack would wait for data from the server, and remote-curl would wait for fetch-pack, causing a deadlock.
Despite this patch, there is other possible malformed input that could cause the same deadlock (e.g. a half-finished pktline, or a pktline but no trailing flush). There are a few possible solutions to this:
1. Allowing remote-curl to tell fetch-pack about the EOF (so that fetch-pack could know that no more data is coming until it says something else). This is tricky because an out-of-band signal would be required, or the http response would have to be re-framed inside another layer of pkt-line or something.
2. Make remote-curl understand some of the protocol. It turns out that in addition to understanding pkt-line, it would need to watch for ack/nak. This is somewhat fragile, as information about the protocol would end up in two places. Also, pkt-lines which are already at the length limit would need special handling.
Both of these solutions would require a fair amount of work, whereas this hack is easy and solves at least some of the problem.
Still to do: it would be good to give a better error message than "fatal: The remote end hung up unexpectedly".
Signed-off-by: David Turner <dturner@twosigma.com> Signed-off-by: Junio C Hamano <gitster@pobox.com> --- remote-curl.c | 8 ++++++++ t/t5551-http-fetch-smart.sh | 30 ++++++++++++++++++++++++++++++ 2 files changed, 38 insertions(+)
diff --git a/remote-curl.c b/remote-curl.c index f14c41f4c0..ee4423659f 100644 --- a/remote-curl.c +++ b/remote-curl.c @@ -400,6 +400,7 @@ struct rpc_state { size_t pos; int in; int out; + int any_written; struct strbuf result; unsigned gzip_request : 1; unsigned initial_buffer : 1; @@ -456,6 +457,8 @@ static size_t rpc_in(char *ptr, size_t eltsize, { size_t size = eltsize * nmemb; struct rpc_state *rpc = buffer_; + if (size) + rpc->any_written = 1; write_or_die(rpc->in, ptr, size); return size; } @@ -659,6 +662,8 @@ static int post_rpc(struct rpc_state *rpc) curl_easy_setopt(slot->curl, CURLOPT_WRITEFUNCTION, rpc_in); curl_easy_setopt(slot->curl, CURLOPT_FILE, rpc); + + rpc->any_written = 0; err = run_slot(slot, NULL); if (err == HTTP_REAUTH && !large_request) { credential_fill(&http_auth); @@ -667,6 +672,9 @@ static int post_rpc(struct rpc_state *rpc) if (err != HTTP_OK) err = -1; + if (!rpc->any_written) + err = -1; + curl_slist_free_all(headers); free(gzip_body); return err; diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh index 1ec5b2747a..43665ab4a8 100755 --- a/t/t5551-http-fetch-smart.sh +++ b/t/t5551-http-fetch-smart.sh @@ -276,6 +276,36 @@ test_expect_success 'large fetch-pack requests can be split across POSTs' ' test_line_count = 2 posts ' +test_expect_success 'test allowreachablesha1inwant' ' + test_when_finished "rm -rf test_reachable.git" && + server="$HTTPD_DOCUMENT_ROOT_PATH/repo.git" && + master_sha=$(git -C "$server" rev-parse refs/heads/master) && + git -C "$server" config uploadpack.allowreachablesha1inwant 1 && + + git init --bare test_reachable.git && + git -C test_reachable.git remote add origin "$HTTPD_URL/smart/repo.git" && + git -C test_reachable.git fetch origin "$master_sha" +' + +test_expect_success 'test allowreachablesha1inwant with unreachable' ' + test_when_finished "rm -rf test_reachable.git; git reset --hard $(git rev-parse HEAD)" && + + #create unreachable sha + echo content >file2 && + git add file2 && + git commit -m two && + git push public HEAD:refs/heads/doomed && + git push public :refs/heads/doomed && + + server="$HTTPD_DOCUMENT_ROOT_PATH/repo.git" && + master_sha=$(git -C "$server" rev-parse refs/heads/master) && + git -C "$server" config uploadpack.allowreachablesha1inwant 1 && + + git init --bare test_reachable.git && + git -C test_reachable.git remote add origin "$HTTPD_URL/smart/repo.git" && + test_must_fail git -C test_reachable.git fetch origin "$(git rev-parse HEAD)" +' + test_expect_success EXPENSIVE 'http can handle enormous ref negotiation' ' ( cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
-- 2.11.0-442-g0c85c54a77