There is a subtle failure happening when computing corrected commit
dates with --split enabled. It requires a base layer needing the
generation_data_overflow chunk. Then, the next layer on top
erroneously thinks it needs an overflow chunk due to a bug leading
to recalculating all reachable generation numbers. The output of
the failure is
BUG: commit-graph.c:1912: expected to write 8 bytes to
chunk 47444f56, but wrote 0 instead
These "expected" 8 bytes are due to re-computing the corrected
commit date for the lower layer but the new layer does not need
any overflow.
Add a test to t5318-commit-graph.sh that demonstrates this bug. However,
it does not trigger consistently with the existing code.
The generation number data is stored in a slab and accessed by
commit_graph_data_at(). This data is initialized when parsing a commit,
but is otherwise used assuming it has been populated. The loop in
compute_generation_numbers() did not enforce that all reachable
commits were parsed and had correct values. This could lead to some
problems when writing a commit-graph with corrected commit dates based
on a commit-graph without them.
It has been difficult to identify the issue here because it was so hard
to reproduce. It relies on this uninitialized data having a non-zero
value, but also on specifically in a way that overwrites the existing
data.
This patch adds the extra parse to ensure the data is filled before we
compute the generation number of a commit. This triggers the new test
to fail because the generation number overflow count does not match
between this computation and the write for that chunk.
The actual fix will follow as the next few changes.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-<commandname>.txt 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.txt
(man gitcvs-migration or git help cvs-migration if git is
installed).
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
