| Message ID | xmqqle1p1367.fsf@gitster.g (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | csum-file: introduce discard_hashfile() | expand |
On Thu, Jul 25, 2024 at 04:07:28PM -0700, Junio C Hamano wrote: > Introduce discard_hashfile() API function to allow them to release > the resources held by a hashfile structure the callers want to > dispose of, and use that in read-cache.c:do_write_index(), which is > a central place that writes the index file. Nicely explained, and the patch looks good to me. A few small comments (that probably do not need any changes): > +void discard_hashfile(struct hashfile *f) > +{ > + if (0 <= f->check_fd) > + close(f->check_fd); > + if (0 <= f->fd) > + close(f->fd); > + free_hashfile(f); > +} I wondered if we could call this function to replace other spots that close the descriptors. But I don't think so. There is only one such spot, in finalize_hashfile(), and it does extra work to make sure that the close succeeds. So it wouldn't make sense to convert, and nobody else (until now) bothered to clean up a discarded hashfile. > diff --git a/read-cache.c b/read-cache.c > index 48bf24f87c..d96a2cb8cf 100644 > --- a/read-cache.c > +++ b/read-cache.c > @@ -2963,7 +2963,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, > > if (err) { > free(ieot); > - return err; > + goto discard_hashfile_and_return; > } > > offset = hashfile_total(f); > @@ -2992,8 +2992,14 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, > hashwrite(f, sb.buf, sb.len); > strbuf_release(&sb); > free(ieot); > - if (err) > - return -1; > + /* > + * NEEDSWORK: write_index_ext_header() never returns a failure, > + * and this part may want to be simplified. > + */ > + if (err) { > + err = -1; > + goto discard_hashfile_and_return; > + } > } There's other repeated cleanup happening here, like free(ieot) and strbuf_release(), which made wonder if we could bump it down to the cleanup label at the end of the function to simplify things. But probably not, as we are often doing that cleanup even in the non-error case. And of course the "sb" strbuf is local to a lot of blocks. So even if we did want to do it, I think it would come as a separate patch. But mostly I wondered whether the label should be a more generic "cleanup" than "discard_hashfile". We could probably worry about that later, though, if that separate patch ever materializes. > @@ -3106,6 +3158,11 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, > istate->cache_nr); > > return 0; > + > +discard_hashfile_and_return: > + if (f) > + discard_hashfile(f); > + return err; > } OK, so here's our cleanup label. We check that "f" is valid. I notice we don't initialize it to NULL, but assigning to it from hashfd() is the very first thing we do, so it will never be uninitialized. Good. That made me wonder when it would ever be NULL, and the answer is that it becomes so after we finalize it: > @@ -3085,13 +3134,16 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, > > finalize_hashfile(f, istate->oid.hash, FSYNC_COMPONENT_INDEX, > CSUM_HASH_IN_STREAM | csum_fsync_flag); > + f = NULL; which makes sense. Arguably finalize_hashfile() could take a pointer-to-pointer and set it to NULL itself for safety/simplicity, but it's probably OK to let the caller deal with it (we do that trick in the tempfile API, but not elsewhere). One thing I did notice. The full hunk above is: > @@ -3085,13 +3134,16 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, > > finalize_hashfile(f, istate->oid.hash, FSYNC_COMPONENT_INDEX, > CSUM_HASH_IN_STREAM | csum_fsync_flag); > + f = NULL; > > if (close_tempfile_gently(tempfile)) { > - error(_("could not close '%s'"), get_tempfile_path(tempfile)); > - return -1; > + err = error(_("could not close '%s'"), get_tempfile_path(tempfile)); > + goto discard_hashfile_and_return; > + } > + if (stat(get_tempfile_path(tempfile), &st)) { > + err = error_errno(_("could not stat '%s'"), get_tempfile_path(tempfile)); > + goto discard_hashfile_and_return; > } > - if (stat(get_tempfile_path(tempfile), &st)) > - return -1; We know that "f" is always NULL at this point, so the new code at the discard_hashfile_and_return label will never actually free anything. We could continue to just "return -1" here and be fine. I am OK with it to keep the general "jump to the cleanup label and return" pattern consistent within the function, but it would make more sense if the label had a less specific name. ;) -Peff
On Fri, Jul 26, 2024 at 12:42:16AM -0400, Jeff King wrote: > On Thu, Jul 25, 2024 at 04:07:28PM -0700, Junio C Hamano wrote: > > > Introduce discard_hashfile() API function to allow them to release > > the resources held by a hashfile structure the callers want to > > dispose of, and use that in read-cache.c:do_write_index(), which is > > a central place that writes the index file. > > Nicely explained, and the patch looks good to me. > > A few small comments (that probably do not need any changes): > > > +void discard_hashfile(struct hashfile *f) > > +{ > > + if (0 <= f->check_fd) > > + close(f->check_fd); > > + if (0 <= f->fd) > > + close(f->fd); > > + free_hashfile(f); > > +} Are we sure that this is always correct? A valid file descriptor may have a zero value, and we wouldn't end up closing it here. > > @@ -2992,8 +2992,14 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, > > hashwrite(f, sb.buf, sb.len); > > strbuf_release(&sb); > > free(ieot); > > - if (err) > > - return -1; > > + /* > > + * NEEDSWORK: write_index_ext_header() never returns a failure, > > + * and this part may want to be simplified. > > + */ > > + if (err) { > > + err = -1; > > + goto discard_hashfile_and_return; > > + } > > } > > There's other repeated cleanup happening here, like free(ieot) and > strbuf_release(), which made wonder if we could bump it down to the > cleanup label at the end of the function to simplify things. But > probably not, as we are often doing that cleanup even in the non-error > case. And of course the "sb" strbuf is local to a lot of blocks. > > So even if we did want to do it, I think it would come as a separate > patch. But mostly I wondered whether the label should be a more generic > "cleanup" than "discard_hashfile". We could probably worry about that > later, though, if that separate patch ever materializes. Indeed, I wanted to say the same. I've got a patch series sitting around locally where I do this. I guess I should send out my memory leak fixes sooner rather than later to avoid duplicated work :) Patrick
Jeff King <peff@peff.net> writes: > There's other repeated cleanup happening here, like free(ieot) and > strbuf_release(), which made wonder if we could bump it down to the > cleanup label at the end of the function to simplify things. But > probably not, as we are often doing that cleanup even in the non-error > case. And of course the "sb" strbuf is local to a lot of blocks. These localized and independent strbuf instances were indeed what discouraged me from moving other clean-up to a central place. > So even if we did want to do it, I think it would come as a separate > patch. But mostly I wondered whether the label should be a more generic > "cleanup" than "discard_hashfile". We could probably worry about that > later, though, if that separate patch ever materializes. Yup, I wobbled between a more generic "cleanup" and "hashfile is the only thing that needs special clean-up right now", and it does show, as you noticed, how the error code paths after calling finalize looks like. I think I'll rename the label to "cleaup". Thanks.
Patrick Steinhardt <ps@pks.im> writes: > On Fri, Jul 26, 2024 at 12:42:16AM -0400, Jeff King wrote: >> On Thu, Jul 25, 2024 at 04:07:28PM -0700, Junio C Hamano wrote: >> >> > Introduce discard_hashfile() API function to allow them to release >> > the resources held by a hashfile structure the callers want to >> > dispose of, and use that in read-cache.c:do_write_index(), which is >> > a central place that writes the index file. >> >> Nicely explained, and the patch looks good to me. >> >> A few small comments (that probably do not need any changes): >> >> > +void discard_hashfile(struct hashfile *f) >> > +{ >> > + if (0 <= f->check_fd) >> > + close(f->check_fd); >> > + if (0 <= f->fd) >> > + close(f->fd); >> > + free_hashfile(f); >> > +} > > Are we sure that this is always correct? A valid file descriptor may > have a zero value, and we wouldn't end up closing it here. I thought that these two fd members use -1 for their "zero value" for that exact reason.
diff --git a/csum-file.c b/csum-file.c index 8abbf01325..2131ee6b12 100644 --- a/csum-file.c +++ b/csum-file.c @@ -102,6 +102,15 @@ int finalize_hashfile(struct hashfile *f, unsigned char *result, return fd; } +void discard_hashfile(struct hashfile *f) +{ + if (0 <= f->check_fd) + close(f->check_fd); + if (0 <= f->fd) + close(f->fd); + free_hashfile(f); +} + void hashwrite(struct hashfile *f, const void *buf, unsigned int count) { while (count) { diff --git a/csum-file.h b/csum-file.h index 566e05cbd2..36c7c5585f 100644 --- a/csum-file.h +++ b/csum-file.h @@ -47,6 +47,7 @@ struct hashfile *hashfd(int fd, const char *name); struct hashfile *hashfd_check(const char *name); struct hashfile *hashfd_throughput(int fd, const char *name, struct progress *tp); int finalize_hashfile(struct hashfile *, unsigned char *, enum fsync_component, unsigned int); +void discard_hashfile(struct hashfile *); void hashwrite(struct hashfile *, const void *, unsigned int); void hashflush(struct hashfile *f); void crc32_begin(struct hashfile *); diff --git a/read-cache.c b/read-cache.c index 48bf24f87c..d96a2cb8cf 100644 --- a/read-cache.c +++ b/read-cache.c @@ -2963,7 +2963,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, if (err) { free(ieot); - return err; + goto discard_hashfile_and_return; } offset = hashfile_total(f); @@ -2992,8 +2992,14 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, hashwrite(f, sb.buf, sb.len); strbuf_release(&sb); free(ieot); - if (err) - return -1; + /* + * NEEDSWORK: write_index_ext_header() never returns a failure, + * and this part may want to be simplified. + */ + if (err) { + err = -1; + goto discard_hashfile_and_return; + } } if (write_extensions & WRITE_SPLIT_INDEX_EXTENSION && @@ -3008,8 +3014,14 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, sb.len) < 0; hashwrite(f, sb.buf, sb.len); strbuf_release(&sb); - if (err) - return -1; + /* + * NEEDSWORK: write_link_extension() never returns a failure, + * and this part may want to be simplified. + */ + if (err) { + err = -1; + goto discard_hashfile_and_return; + } } if (write_extensions & WRITE_CACHE_TREE_EXTENSION && !drop_cache_tree && istate->cache_tree) { @@ -3019,8 +3031,14 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, err = write_index_ext_header(f, eoie_c, CACHE_EXT_TREE, sb.len) < 0; hashwrite(f, sb.buf, sb.len); strbuf_release(&sb); - if (err) - return -1; + /* + * NEEDSWORK: write_index_ext_header() never returns a failure, + * and this part may want to be simplified. + */ + if (err) { + err = -1; + goto discard_hashfile_and_return; + } } if (write_extensions & WRITE_RESOLVE_UNDO_EXTENSION && istate->resolve_undo) { @@ -3031,8 +3049,14 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, sb.len) < 0; hashwrite(f, sb.buf, sb.len); strbuf_release(&sb); - if (err) - return -1; + /* + * NEEDSWORK: write_index_ext_header() never returns a failure, + * and this part may want to be simplified. + */ + if (err) { + err = -1; + goto discard_hashfile_and_return; + } } if (write_extensions & WRITE_UNTRACKED_CACHE_EXTENSION && istate->untracked) { @@ -3043,8 +3067,14 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, sb.len) < 0; hashwrite(f, sb.buf, sb.len); strbuf_release(&sb); - if (err) - return -1; + /* + * NEEDSWORK: write_index_ext_header() never returns a failure, + * and this part may want to be simplified. + */ + if (err) { + err = -1; + goto discard_hashfile_and_return; + } } if (write_extensions & WRITE_FSMONITOR_EXTENSION && istate->fsmonitor_last_update) { @@ -3054,12 +3084,25 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, err = write_index_ext_header(f, eoie_c, CACHE_EXT_FSMONITOR, sb.len) < 0; hashwrite(f, sb.buf, sb.len); strbuf_release(&sb); - if (err) - return -1; + /* + * NEEDSWORK: write_index_ext_header() never returns a failure, + * and this part may want to be simplified. + */ + if (err) { + err = -1; + goto discard_hashfile_and_return; + } } if (istate->sparse_index) { - if (write_index_ext_header(f, eoie_c, CACHE_EXT_SPARSE_DIRECTORIES, 0) < 0) - return -1; + err = write_index_ext_header(f, eoie_c, CACHE_EXT_SPARSE_DIRECTORIES, 0); + /* + * NEEDSWORK: write_index_ext_header() never returns a failure, + * and this part may want to be simplified. + */ + if (err) { + err = -1; + goto discard_hashfile_and_return; + } } /* @@ -3075,8 +3118,14 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, err = write_index_ext_header(f, NULL, CACHE_EXT_ENDOFINDEXENTRIES, sb.len) < 0; hashwrite(f, sb.buf, sb.len); strbuf_release(&sb); - if (err) - return -1; + /* + * NEEDSWORK: write_index_ext_header() never returns a failure, + * and this part may want to be simplified. + */ + if (err) { + err = -1; + goto discard_hashfile_and_return; + } } csum_fsync_flag = 0; @@ -3085,13 +3134,16 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, finalize_hashfile(f, istate->oid.hash, FSYNC_COMPONENT_INDEX, CSUM_HASH_IN_STREAM | csum_fsync_flag); + f = NULL; if (close_tempfile_gently(tempfile)) { - error(_("could not close '%s'"), get_tempfile_path(tempfile)); - return -1; + err = error(_("could not close '%s'"), get_tempfile_path(tempfile)); + goto discard_hashfile_and_return; + } + if (stat(get_tempfile_path(tempfile), &st)) { + err = error_errno(_("could not stat '%s'"), get_tempfile_path(tempfile)); + goto discard_hashfile_and_return; } - if (stat(get_tempfile_path(tempfile), &st)) - return -1; istate->timestamp.sec = (unsigned int)st.st_mtime; istate->timestamp.nsec = ST_MTIME_NSEC(st); trace_performance_since(start, "write index, changed mask = %x", istate->cache_changed); @@ -3106,6 +3158,11 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, istate->cache_nr); return 0; + +discard_hashfile_and_return: + if (f) + discard_hashfile(f); + return err; } void set_alternate_index_output(const char *name) diff --git a/t/t2107-update-index-basic.sh b/t/t2107-update-index-basic.sh index cc72ead79f..f0eab13f96 100755 --- a/t/t2107-update-index-basic.sh +++ b/t/t2107-update-index-basic.sh @@ -5,6 +5,7 @@ test_description='basic update-index tests Tests for command-line parsing and basic operation. ' +TEST_PASSES_SANITIZE_LEAK=true . ./test-lib.sh test_expect_success 'update-index --nonsense fails' '
The hashfile API is used to write out a "hashfile", which has a final checksum (typically SHA-1) at the end. An in-core hashfile structure has up to two file descriptors and a few buffers that can only be freed by calling a helper function that is private to the csum-file implementation. The usual flow of a user of the API is to first open a file descriptor for writing, obtain a hashfile associated with that write file descriptor by calling either hashfd() or hashfd_check(), call hashwrite() number of times to write data to the file, and then call finalize_hashfile(), which appends th checksum to the end of the file, closes file descriptors and releases associated buffers. But what if a caller finds some error after calling hashfd() to start the process and/or hashwrite() to send some data to the file, and wants to abort the operation? The underlying file descriptor is often managed by the tempfile API, so aborting will clean the file out of the filesystem, but the resources associated with the in-core hashfile structure is lost. Introduce discard_hashfile() API function to allow them to release the resources held by a hashfile structure the callers want to dispose of, and use that in read-cache.c:do_write_index(), which is a central place that writes the index file. Mark t2107 as leak-free, as this leak in "update-index --cacheinfo" test that deliberately makes it fail is now plugged. Signed-off-by: Junio C Hamano <gitster@pobox.com> --- csum-file.c | 9 ++++ csum-file.h | 1 + read-cache.c | 99 +++++++++++++++++++++++++++-------- t/t2107-update-index-basic.sh | 1 + 4 files changed, 89 insertions(+), 21 deletions(-)