Merge branch 'jk/http-backend-deadlock' into maint

Communication between the HTTP server and http_backend process can
lead to a dead-lock when relaying a large ref negotiation request.
Diagnose the situation better, and mitigate it by reading such a
request first into core (to a reasonable limit).

* jk/http-backend-deadlock:
http-backend: spool ref negotiation requests to buffer
t5551: factor out tag creation
http-backend: fix die recursion with custom handler

diff --combined Documentation/git-http-backend.txt
index 3ca18c4de519ebdf0a2af6509d0d6bed3e6e492c,8c6acbe440c8c9a2df8cbe5b3a13a4b355c9e0ac..9268fb6b1ea2de2b29fb077a1a675c727526abeb
--- 1/Documentation/git-http-backend.txt
--- 2/Documentation/git-http-backend.txt
+++ b/Documentation/git-http-backend.txt
@@@ -65,8 -65,8 +65,8 @@@ automatically by the web server
  
  EXAMPLES
  --------
 -All of the following examples map 'http://$hostname/git/foo/bar.git'
 -to '/var/www/git/foo/bar.git'.
 +All of the following examples map `http://$hostname/git/foo/bar.git`
 +to `/var/www/git/foo/bar.git`.
  
  Apache 2.x::
        Ensure mod_cgi, mod_alias, and mod_env are enabled, set
@@@ -255,6 -255,15 +255,15 @@@ The GIT_HTTP_EXPORT_ALL environmental v
  'git-http-backend' to bypass the check for the "git-daemon-export-ok"
  file in each repository before allowing export of that repository.
  
+ The `GIT_HTTP_MAX_REQUEST_BUFFER` environment variable (or the
+ `http.maxRequestBuffer` config variable) may be set to change the
+ largest ref negotiation request that git will handle during a fetch; any
+ fetch requiring a larger buffer will not succeed.  This value should not
+ normally need to be changed, but may be helpful if you are fetching from
+ a repository with an extremely large number of refs.  The value can be
+ specified with a unit (e.g., `100M` for 100 megabytes). The default is
+ 10 megabytes.
+ 
  The backend process sets GIT_COMMITTER_NAME to '$REMOTE_USER' and
  GIT_COMMITTER_EMAIL to '$\{REMOTE_USER}@http.$\{REMOTE_ADDR\}',
  ensuring that any reflogs created by 'git-receive-pack' contain some

diff --combined t/t5551-http-fetch-smart.sh
index 2b293119015af7bfb8f151d2a3ec8c51c4c0b209,a540c6da23782c47a08b2e7bc684d68fe8e80934..58207d88250f57d448f4e83baf2add3192cb9455
--- 1/t/t5551-http-fetch-smart.sh
--- 2/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@@ -2,6 -2,12 +2,6 @@@
  
  test_description='test smart fetching over http via http-backend'
  . ./test-lib.sh
 -
 -if test -n "$NO_CURL"; then
 -      skip_all='skipping test, git built without http support'
 -      test_done
 -fi
 -
  . "$TEST_DIRECTORY"/lib-httpd.sh
  start_httpd
  
@@@ -218,27 -224,35 +218,35 @@@ test_expect_success 'transfer.hiderefs 
        git -C hidden.git rev-parse --verify b
  '
  
- test_expect_success 'create 2,000 tags in the repo' '
-       (
-       cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
-       for i in $(test_seq 2000)
+ # create an arbitrary number of tags, numbered from tag-$1 to tag-$2
+ create_tags () {
+       rm -f marks &&
+       for i in $(test_seq "$1" "$2")
        do
-               echo "commit refs/heads/too-many-refs"
-               echo "mark :$i"
-               echo "committer git <git@example.com> $i +0000"
-               echo "data 0"
-               echo "M 644 inline bla.txt"
-               echo "data 4"
-               echo "bla"
+               # don't use here-doc, because it requires a process
+               # per loop iteration
+               echo "commit refs/heads/too-many-refs-$1" &&
+               echo "mark :$i" &&
+               echo "committer git <git@example.com> $i +0000" &&
+               echo "data 0" &&
+               echo "M 644 inline bla.txt" &&
+               echo "data 4" &&
+               echo "bla" &&
                # make every commit dangling by always
                # rewinding the branch after each commit
-               echo "reset refs/heads/too-many-refs"
-               echo "from :1"
+               echo "reset refs/heads/too-many-refs-$1" &&
+               echo "from :$1"
        done | git fast-import --export-marks=marks &&
  
        # now assign tags to all the dangling commits we created above
        tag=$(perl -e "print \"bla\" x 30") &&
        sed -e "s|^:\([^ ]*\) \(.*\)$|\2 refs/tags/$tag-\1|" <marks >>packed-refs
+ }
+ 
+ test_expect_success 'create 2,000 tags in the repo' '
+       (
+               cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+               create_tags 1 2000
        )
  '
  
@@@ -259,5 -273,20 +267,20 @@@ test_expect_success 'large fetch-pack r
        test_line_count = 2 posts
  '
  
+ test_expect_success EXPENSIVE 'http can handle enormous ref negotiation' '
+       (
+               cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+               create_tags 2001 50000
+       ) &&
+       git -C too-many-refs fetch -q --tags &&
+       (
+               cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+               create_tags 50001 100000
+       ) &&
+       git -C too-many-refs fetch -q --tags &&
+       git -C too-many-refs for-each-ref refs/tags >tags &&
+       test_line_count = 100000 tags
+ '
+ 
  stop_httpd
  test_done