Re: [PATCH] tmp-objdir: do not opendir() when handling a signal

>     tmp-objdir: do not closedir() when handling a signal
>     
>     We have recently observed a Git process hanging around for weeks. A
>     backtrace revealed that a git-receive-pack(1) process was deadlocked
>     when trying to remove the quarantine directory "incoming." It turns out
>     that the tmp_objdir API calls opendir(3) and closedir(3) to observe a
>     directory's contents in order to remove all the contents before removing
>     the directory itself. These functions are not async signal save as they
>     allocate and free memory.
>     
>     The fix is to avoid calling these functions when handling a signal in
>     order to avoid a deadlock. The implication of such a fix however, is
>     that temporary object directories may not get cleaned up properly when a
>     signal is being handled. The tradeoff this fix is making is to prevent
>     deadlocks at the cost of temporary object directory cleanup.
>     
>     This is similar to 58d4d7f1c5 (2022-01-07 fetch: fix deadlock when
>     cleaning up lockfiles in async signals)

>  static int remove_dir_recurse(struct strbuf *path, int flag, int *kept_up)
>  {
> -	DIR *dir;
> +	DIR *dir = NULL;
>  	struct dirent *e;
>  	int ret = 0, original_len = path->len, len, kept_down = 0;
>  	int only_empty = (flag & REMOVE_DIR_EMPTY_ONLY);
> @@ -3261,7 +3261,10 @@ static int remove_dir_recurse(struct strbuf *path, int flag, int *kept_up)
>  	}
>  
>  	flag &= ~REMOVE_DIR_KEEP_TOPLEVEL;
> -	dir = opendir(path->buf);
> +
> +	if ((flag & REMOVE_DIR_SIGNAL) == 0)
> +		dir = opendir(path->buf);
> +
>  	if (!dir) {
>  		if (errno == ENOENT)
>  			return keep_toplevel ? -1 : 0;
> diff --git a/dir.h b/dir.h
> index 674747d93af..ba159f4abeb 100644
> --- a/dir.h
> +++ b/dir.h
> @@ -498,6 +498,9 @@ int get_sparse_checkout_patterns(struct pattern_list *pl);
>  /* Remove the_original_cwd too */
>  #define REMOVE_DIR_PURGE_ORIGINAL_CWD 0x08
>  
> +/* Indicates a signal is being handled */
> +#define REMOVE_DIR_SIGNAL 0x16
> +
>  /*
>   * Remove path and its contents, recursively. flags is a combination
>   * of the above REMOVE_DIR_* constants. Return 0 on success.
> diff --git a/tmp-objdir.c b/tmp-objdir.c