7270956809
Before using any of the commit-graph bloom-filter code, somebody needs
to call init_bloom_filters(). This initializes the commit-slab we use
for storing filter information. But we don't want to call it twice
(without a matching deinit call in the middle), since it overwrites the
existing slab pointers, leaking the old values.
Usually this init call is done lazily by parse_commit_graph() when we
read a graph file that contains bloom data. But this can lead to some
oddities:
1. We may call parse_commit_graph() multiple times when we have a
split commit graph. I think this doesn't produce any user-visible
bug, because we parse all of the files back-to-back. So even though
we call init_bloom_filters() multiple times, we never look up any
commits in between, so the slab is always empty and initializing it
again happens to do nothing. This is a little sketchy to rely on,
though.
2. We call init_bloom_filters() directly in the "test-tool bloom"
helper so we can call get_or_compute_bloom_filter(). Normally this
is OK, as there is no bloom data in the on-disk graph file. But if
you build with SANITIZE=leak and run:
GIT_TEST_COMMIT_GRAPH=1 \
GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=1 \
./t0095-bloom.sh
there's a leak that happens like this:
a. Our direct init_bloom_filters() sets up the slab.
b. In get_or_compute_bloom_filter() we look in the slab for a
cached entry. We won't find anything yet, but since we don't
use the read-only "peek" accessor (since we'll fill in the
entry if not present), this actually populates the slab with
an allocated chunk.
c. Now we look for an entry in the graph files. So we have to
load them and end up in parse_commit_graph(), which calls
init_bloom_filters() again. That trashes our existing slab
allocation, which is now leaked.
3. There's a similar case in write_commit_graph(), which calls
init_bloom_filters() before get_or_compute_bloom_filter(). I think
this code path is lucky to avoid the leak because it reads the
graph files first, then calls its init_bloom_filters(), and then
starts filling in entries. So even though it has the same overwrite
problem, we'd never actually allocate any slab entries between
overwrites.
The easiest solution here is just to make initialization of the slab
idempotent using an extra flag.
We could actually get away without using the extra flag, for example by
checking whether bloom_filters.stride has been set. But it's probably
better to avoid being too intimate with the commit-slab details.
Likewise we don't actually need to re-initialize after a deinit call;
the slab-clearing function leaves things in a usable state. But it
seemed less surprising to pair the init/deinit calls explicitly.
I suspect this could all be cleaned up a bit more, but it's tricky. The
only function which uses the slab is get_or_compute_bloom_filter(), so
it would be much simpler if it just lazy-initialized the slab itself.
But I think there is a subtle dependency here: we usually only
initialize the slab when we find a graph file that has bloom entries. So
if we were to lose that signal, then even repos without on-disk bloom
data would start trying to populate the slab, wasting memory that will
never get entries filled in from the disk. So we'd need some other way
of signaling "it is worth considering bloom entries at all".
This patch takes a smaller and more direct route to just dealing with
the potential leak issue.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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| Documentation | ||
| bin-wrappers | ||
| block-sha1 | ||
| builtin | ||
| ci | ||
| compat | ||
| compiler-tricks | ||
| contrib | ||
| ewah | ||
| git-gui | ||
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| gitweb | ||
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| perl | ||
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| refs | ||
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| sha1 | ||
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| t | ||
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| tools | ||
| trace2 | ||
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| CODE_OF_CONDUCT.md | ||
| COPYING | ||
| Cargo.toml | ||
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| INSTALL | ||
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| Makefile | ||
| README.md | ||
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| SECURITY.md | ||
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| common-exit.c | ||
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| config.c | ||
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| exec-cmd.c | ||
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| fsmonitor-ipc.c | ||
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| gettext.c | ||
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| git-archimport.perl | ||
| git-compat-util.h | ||
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| git-filter-branch.sh | ||
| git-instaweb.sh | ||
| git-merge-octopus.sh | ||
| git-merge-one-file.sh | ||
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| git.c | ||
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| gpg-interface.c | ||
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| graph.c | ||
| graph.h | ||
| grep.c | ||
| grep.h | ||
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| hex.h | ||
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| http-backend.c | ||
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| object.c | ||
| object.h | ||
| odb.c | ||
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| oidset.h | ||
| oidtree.c | ||
| oidtree.h | ||
| pack-bitmap-write.c | ||
| pack-bitmap.c | ||
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| pack-check.c | ||
| pack-mtimes.c | ||
| pack-mtimes.h | ||
| pack-objects.c | ||
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| pack-refs.c | ||
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| pack-revindex.c | ||
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| pack.h | ||
| packfile.c | ||
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| pager.c | ||
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| parse-options.h | ||
| parse.c | ||
| parse.h | ||
| patch-delta.c | ||
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| path.c | ||
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| pretty.c | ||
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| prune-packed.c | ||
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| reachable.c | ||
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| rebase-interactive.c | ||
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| rebase.h | ||
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| reflog-walk.c | ||
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| refs.c | ||
| refs.h | ||
| refspec.c | ||
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| remote.c | ||
| remote.h | ||
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| sh-i18n--envsubst.c | ||
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| shared.mak | ||
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README.md
Git - fast, scalable, distributed revision control system
Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.
Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.adoc to get started, then see
Documentation/giteveryday.adoc for a useful minimum set of commands, and
Documentation/git-<commandname>.adoc for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with man gittutorial or git help tutorial, and the
documentation of each command with man git-<commandname> or git help <commandname>.
CVS users may also want to read Documentation/gitcvs-migration.adoc
(man gitcvs-migration or git help cvs-migration if git is
installed).
The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission and Documentation/CodingGuidelines).
Those wishing to help with error message, usage and informational message
string translations (localization l10) should see po/README.md
(a po file is a Portable Object file that holds the translations).
To subscribe to the list, send an email to git+subscribe@vger.kernel.org (see https://subspace.kernel.org/subscribing.html for details). The mailing list archives are available at https://lore.kernel.org/git/, https://marc.info/?l=git and other archival sites.
Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.
The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (depending on your mood):
- random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
- "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks