diff --git a/reftable/stack.c b/reftable/stack.c index 54982e0f7d..3f13c3eb34 100644 --- a/reftable/stack.c +++ b/reftable/stack.c @@ -1020,7 +1020,9 @@ static int stack_compact_range(struct reftable_stack *st, struct lock_file *table_locks = NULL; struct tempfile *new_table = NULL; int is_empty_table = 0, err = 0; + size_t first_to_replace, last_to_replace; size_t i, nlocks = 0; + char **names = NULL; if (first > last || (!expiry && first == last)) { err = 0; @@ -1123,6 +1125,100 @@ static int stack_compact_range(struct reftable_stack *st, } } + /* + * As we have unlocked the stack while compacting our slice of tables + * it may have happened that a concurrently running process has updated + * the stack while we were compacting. In that case, we need to check + * whether the tables that we have just compacted still exist in the + * stack in the exact same order as we have compacted them. + * + * If they do exist, then it is fine to continue and replace those + * tables with our compacted version. If they don't, then we need to + * abort. + */ + err = stack_uptodate(st); + if (err < 0) + goto done; + if (err > 0) { + ssize_t new_offset = -1; + int fd; + + fd = open(st->list_file, O_RDONLY); + if (fd < 0) { + err = REFTABLE_IO_ERROR; + goto done; + } + + err = fd_read_lines(fd, &names); + close(fd); + if (err < 0) + goto done; + + /* + * Search for the offset of the first table that we have + * compacted in the updated "tables.list" file. + */ + for (size_t i = 0; names[i]; i++) { + if (strcmp(names[i], st->readers[first]->name)) + continue; + + /* + * We have found the first entry. Verify that all the + * subsequent tables we have compacted still exist in + * the modified stack in the exact same order as we + * have compacted them. + */ + for (size_t j = 1; j < last - first + 1; j++) { + const char *old = first + j < st->merged->stack_len ? + st->readers[first + j]->name : NULL; + const char *new = names[i + j]; + + /* + * If some entries are missing or in case the tables + * have changed then we need to bail out. Again, this + * shouldn't ever happen because we have locked the + * tables we are compacting. + */ + if (!old || !new || strcmp(old, new)) { + err = REFTABLE_OUTDATED_ERROR; + goto done; + } + } + + new_offset = i; + break; + } + + /* + * In case we didn't find our compacted tables in the stack we + * need to bail out. In theory, this should have never happened + * because we locked the tables we are compacting. + */ + if (new_offset < 0) { + err = REFTABLE_OUTDATED_ERROR; + goto done; + } + + /* + * We have found the new range that we want to replace, so + * let's update the range of tables that we want to replace. + */ + first_to_replace = new_offset; + last_to_replace = last + (new_offset - first); + } else { + /* + * `fd_read_lines()` uses a `NULL` sentinel to indicate that + * the array is at its end. As we use `free_names()` to free + * the array, we need to include this sentinel value here and + * thus have to allocate `stack_len + 1` many entries. + */ + REFTABLE_CALLOC_ARRAY(names, st->merged->stack_len + 1); + for (size_t i = 0; i < st->merged->stack_len; i++) + names[i] = xstrdup(st->readers[i]->name); + first_to_replace = first; + last_to_replace = last; + } + /* * If the resulting compacted table is not empty, then we need to move * it into place now. @@ -1145,12 +1241,12 @@ static int stack_compact_range(struct reftable_stack *st, * have just written. In case the compacted table became empty we * simply skip writing it. */ - for (i = 0; i < first; i++) - strbuf_addf(&tables_list_buf, "%s\n", st->readers[i]->name); + for (i = 0; i < first_to_replace; i++) + strbuf_addf(&tables_list_buf, "%s\n", names[i]); if (!is_empty_table) strbuf_addf(&tables_list_buf, "%s\n", new_table_name.buf); - for (i = last + 1; i < st->merged->stack_len; i++) - strbuf_addf(&tables_list_buf, "%s\n", st->readers[i]->name); + for (i = last_to_replace + 1; names[i]; i++) + strbuf_addf(&tables_list_buf, "%s\n", names[i]); err = write_in_full(get_lock_file_fd(&tables_list_lock), tables_list_buf.buf, tables_list_buf.len); @@ -1203,9 +1299,10 @@ done: delete_tempfile(&new_table); strbuf_release(&new_table_name); strbuf_release(&new_table_path); - strbuf_release(&tables_list_buf); strbuf_release(&table_name); + free_names(names); + return err; }