If the original version of `write_locked_index()` returned with an
error, it didn't roll back the lockfile unless the error occured at the
very end, during closing/committing. See commit 03b866477 (read-cache:
new API write_locked_index instead of write_index/write_cache,
2014-06-13).
In commit 9f41c7a6b (read-cache: close index.lock in do_write_index,
2017-04-26), we learned to close the lock slightly earlier in the
callstack. That was mostly a side-effect of lockfiles being implemented
using temporary files, but didn't cause any real harm.
Recently, commit 076aa2cbd (tempfile: auto-allocate tempfiles on heap,
2017-09-05) introduced a subtle bug. If the temporary file is deleted
(i.e., the lockfile is rolled back), the tempfile-pointer in the `struct
lock_file` will be left dangling. Thus, an attempt to reuse the
lockfile, or even just to roll it back, will induce undefined behavior
-- most likely a crash.
Besides not crashing, we clearly want to make things consistent. The
guarantees which the lockfile-machinery itself provides is A) if we ask
to commit and it fails, roll back, and B) if we ask to close and it
fails, do _not_ roll back. Let's do the same for consistency.
Do not delete the temporary file in `do_write_index()`. One of its
callers, `write_locked_index()` will thereby avoid rolling back the
lock. The other caller, `write_shared_index()`, will delete its
temporary file anyway. Both of these callers will avoid undefined
behavior (crashing).
Teach `write_locked_index(..., COMMIT_LOCK)` to roll back the lock
before returning. If we have already succeeded and committed, it will be
a noop. Simplify the existing callers where we now have a superfluous
call to `rollback_lockfile()`. That should keep future readers from
wondering why the callers are inconsistent.
Signed-off-by: Martin Ågren <martin.ag...@gmail.com>
---
v3: Maybe the commit message wasn't too long, but it was loong. For
example, some of it just duplicated stuff from the previous patch.
builtin/difftool.c | 1 -
cache.h | 4 ++++
merge.c | 4 +---
read-cache.c | 14 ++++++++------
sequencer.c | 1 -
5 files changed, 13 insertions(+), 11 deletions(-)
diff --git a/builtin/difftool.c b/builtin/difftool.c
index b2d3ba753..bcc79d188 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -616,7 +616,6 @@ static int run_dir_diff(const char *extcmd, int symlinks,
const char *prefix,
if (hold_lock_file_for_update(&lock, buf.buf, 0) < 0 ||
write_locked_index(&wtindex, &lock, COMMIT_LOCK)) {
ret = error("could not write %s", buf.buf);
- rollback_lock_file(&lock);
goto finish;
}
changed_files(&wt_modified, buf.buf, workdir);
diff --git a/cache.h b/cache.h
index 21a6856c5..0e26224b9 100644
--- a/cache.h
+++ b/cache.h
@@ -616,6 +616,10 @@ extern int read_index_unmerged(struct index_state *);
* split index to the lockfile. If the temporary file for the shared
* index cannot be created, fall back to the behavior described in
* the previous paragraph.
+ *
+ * With `COMMIT_LOCK`, the lock is always committed or rolled back.
+ * Without it, the lock is closed, but neither committed nor rolled
+ * back.
*/
extern int write_locked_index(struct index_state *, struct lock_file *lock,
unsigned flags);
diff --git a/merge.c b/merge.c
index a18a452b5..e5d796c9f 100644
--- a/merge.c
+++ b/merge.c
@@ -91,9 +91,7 @@ int checkout_fast_forward(const struct object_id *head,
}
if (unpack_trees(nr_trees, t, &opts))
return -1;
- if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK)) {
- rollback_lock_file(&lock_file);
+ if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
return error(_("unable to write new index file"));
- }
return 0;
}
diff --git a/read-cache.c b/read-cache.c
index c7aa3632a..0d8d2dede 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2182,9 +2182,8 @@ static int has_racy_timestamp(struct index_state *istate)
void update_index_if_able(struct index_state *istate, struct lock_file
*lockfile)
{
if ((istate->cache_changed || has_racy_timestamp(istate)) &&
- verify_index(istate) &&
- write_locked_index(istate, lockfile, COMMIT_LOCK))
- rollback_lock_file(lockfile);
+ verify_index(istate))
+ write_locked_index(istate, lockfile, COMMIT_LOCK);
}
/*
@@ -2321,7 +2320,6 @@ static int do_write_index(struct index_state *istate,
struct tempfile *tempfile,
return -1;
if (close_tempfile_gently(tempfile)) {
error(_("could not close '%s'"), tempfile->filename.buf);
- delete_tempfile(&tempfile);
return -1;
}
if (stat(tempfile->filename.buf, &st))
@@ -2501,7 +2499,8 @@ int write_locked_index(struct index_state *istate, struct
lock_file *lock,
(istate->cache_changed & ~EXTMASK)) {
if (si)
hashclr(si->base_sha1);
- return do_write_locked_index(istate, lock, flags);
+ ret = do_write_locked_index(istate, lock, flags);
+ goto out;
}
if (getenv("GIT_TEST_SPLIT_INDEX")) {
@@ -2517,7 +2516,7 @@ int write_locked_index(struct index_state *istate, struct
lock_file *lock,
if (new_shared_index) {
ret = write_shared_index(istate, lock, flags);
if (ret)
- return ret;
+ goto out;
}
ret = write_split_index(istate, lock, flags);
@@ -2526,6 +2525,9 @@ int write_locked_index(struct index_state *istate, struct
lock_file *lock,
if (!ret && !new_shared_index)
freshen_shared_index(sha1_to_hex(si->base_sha1), 1);
+out:
+ if (flags & COMMIT_LOCK)
+ rollback_lock_file(lock);
return ret;
}
diff --git a/sequencer.c b/sequencer.c
index 60636ce54..d56c38081 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1183,7 +1183,6 @@ static int read_and_refresh_cache(struct replay_opts
*opts)
refresh_index(&the_index, REFRESH_QUIET|REFRESH_UNMERGED, NULL, NULL,
NULL);
if (the_index.cache_changed && index_fd >= 0) {
if (write_locked_index(&the_index, &index_lock, COMMIT_LOCK)) {
- rollback_lock_file(&index_lock);
return error(_("git %s: failed to refresh the index"),
_(action_name(opts)));
}
--
2.15.0.rc0
