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Jeff King abd5a00268 clear_delta_base_cache(): don't modify hashmap while iterating On Thu, Jan 19, 2017 at 03:03:46PM +0100, Ulrich Spörlein wrote: > > I suspect the patch below may fix things for you. It works around it by > > walking over the lru list (either is fine, as they both contain all > > entries, and since we're clearing everything, we don't care about the > > order). > > Confirmed. With the patch applied, I can import the whole 55G in one go > without any crashes or aborts. Thanks much! Thanks. Here it is rolled up with a commit message. -- >8 -- Subject: clear_delta_base_cache(): don't modify hashmap while iterating Removing entries while iterating causes fast-import to access an already-freed `struct packed_git`, leading to various confusing errors. What happens is that clear_delta_base_cache() drops the whole contents of the cache by iterating over the hashmap, calling release_delta_base_cache() on each entry. That function removes the item from the hashmap. The hashmap code may then shrink the table, but the hashmap_iter struct retains an offset from the old table. As a result, the next call to hashmap_iter_next() may claim that the iteration is done, even though some items haven't been visited. The only caller of clear_delta_base_cache() is fast-import, which wants to clear the cache because it is discarding the packed_git struct for its temporary pack. So by failing to remove all of the entries, we still have references to the freed packed_git. To make things even more confusing, this doesn't seem to trigger with the test suite, because it depends on complexities like the size of the hash table, which entries got cleared, whether we try to access them before they're evicted from the cache, etc. So I've been able to identify the problem with large imports like freebsd's svn import, or a fast-export of linux.git. But nothing that would be reasonable to run as part of the normal test suite. We can fix this easily by iterating over the lru linked list instead of the hashmap. They both contain the same entries, and we can use the "safe" variant of the list iterator, which exists for exactly this case. Let's also add a warning to the hashmap API documentation to reduce the chances of getting bit by this again. Reported-by: Ulrich Spörlein <uqs@freebsd.org> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>		2017-01-19 11:17:20 -08:00
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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 http://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-.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).

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). To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org. The mailing list archives are available at https://public-inbox.org/git, http://marc.info/?l=git and other archival sites.

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