[PATCH v2] receive-pack: fix stale packfile locks when dying
- From
Patrick Steinhardt <ps@pks.im>
- Date
- Mar 10, 2023, 06:52 UTC
- Message-ID
- <e1ee1d8026a361bc58d16bc741e2b347ada7a53e.1678431076.git.ps@pks.im>
- In-Reply-To
- <e16bd81bf9e251aa6959fbe10a3fbc215a4a1c12.1678367338.git.ps@pks.im>
When accepting a packfile in git-receive-pack(1), we feed that packfile into git-index-pack(1) to generate the packfile index. As the packfile would often only contain unreachable objects until the references have been updated, concurrently running garbage collection might be tempted to delete the packfile right away and thus cause corruption. To fix this, we ask git-index-pack(1) to create a `.keep` file before moving the packfile into place, which is getting deleted again once all of the reference updates have been processed.
Now in production systems we have observed that those `.keep` files are sometimes not getting deleted as expected, where the result is that repositories tend to grow packfiles that are never deleted over time. This seems to be caused by a race when git-receive-pack(1) is killed after we have migrated the kept packfile from the quarantine directory into the main object database. While this race window is typically small it can be extended for example by installing a `proc-receive` hook.
Fix this race by registering the lockfile as a tempfile so that it will automatically be removed at exit or when receiving a signal.
Helped-by: Jeff King <peff@peff.net> Signed-off-by: Patrick Steinhardt <ps@pks.im> --- builtin/receive-pack.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c index cd5c7a28ef..b5369d7429 100644 --- a/builtin/receive-pack.c +++ b/builtin/receive-pack.c @@ -2184,7 +2184,7 @@ static const char *parse_pack_header(struct pack_header *hdr) } } -static const char *pack_lockfile; +static struct tempfile *pack_lockfile; static void push_header_arg(struct strvec *args, struct pack_header *hdr) { @@ -2251,6 +2251,7 @@ static const char *unpack(int err_fd, struct shallow_info *si) return "unpack-objects abnormal exit"; } else { char hostname[HOST_NAME_MAX + 1]; + char *lockfile; strvec_pushl(&child.args, "index-pack", "--stdin", NULL); push_header_arg(&child.args, &hdr); @@ -2280,8 +2281,14 @@ static const char *unpack(int err_fd, struct shallow_info *si) status = start_command(&child); if (status) return "index-pack fork failed"; - pack_lockfile = index_pack_lockfile(child.out, NULL); + + lockfile = index_pack_lockfile(child.out, NULL); + if (lockfile) { + pack_lockfile = register_tempfile(lockfile); + free(lockfile); + } close(child.out); + status = finish_command(&child); if (status) return "index-pack abnormal exit"; @@ -2568,8 +2575,7 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix) use_keepalive = KEEPALIVE_ALWAYS; execute_commands(commands, unpack_status, &si, &push_options); - if (pack_lockfile) - unlink_or_warn(pack_lockfile); + delete_tempfile(&pack_lockfile); sigchain_push(SIGPIPE, SIG_IGN); if (report_status_v2) report_v2(commands, unpack_status);
-- 2.40.0.rc0