[LTP] [PATCH 1/1] fs/racer: Fix LTP hang caused by fs_racer.sh

[Li Wang]

On Fri, Jun 11, 2021 at 1:58 AM Leo Yu-Chi Liang <ycliang@andestech.com> wrote:
>
> fs_racer.sh test could cause LTP to hang if the file
> gets removed when it's at time same time being renamed.
>
> The if statement in mv source implemented by busybox is as follows:
>
>         if (dest_exists) {
>                 if (flags & OPT_NOCLOBBER)
>                         goto RET_0;
>                 if (!(flags & OPT_FORCE)           // OPT_FORCE is set by -f option
>                  && ((access(dest, W_OK) < 0 && isatty(0))
>                     || (flags & OPT_INTERACTIVE))  // this is set by -i option
>                 ) {
>                         if (fprintf(stderr, "mv: overwrite '%s'? ", dest) < 0) {
>                                 goto RET_1;  /* Ouch! fprintf failed! */
>                         }
>                         if (!bb_ask_y_confirmation()) {
>                                 goto RET_0;
>                         }
>                 }
>         }
>
> If somehow the dest_file exists when mv executes the first if "if (dest_exists)",
> and gets removed when mv executes the third if "if (access(...))".
> Then it is possible for mv to reach "bb_ask_y_confirmation" and to try to read from tty.
>
> However, the mv process is executing in the background,
> so when it tries to read from tty,
> the processes in the same process group as mv would all receive SIGTTIN
> and be changed into TASK_STOPPED state.
>
> This would cause this testcase to hang, though happens rarely.
>
> Add -f option to suppress the attempt to read from tty.
>
> Signed-off-by: Leo Yu-Chi Liang <ycliang@andestech.com>

Reviewed-by: Li Wang <liwang@redhat.com>

-- 
Regards,
Li Wang