On Wed, Feb 3, 2021 at 2:39 AM Theodore Ts'o <tytso@xxxxxxx> wrote:
>
> On Tue, Feb 02, 2021 at 04:28:37PM +0000, Vinicius Tinti wrote:
> > Clang with -Wunreachable-code-aggressive is being used to try to find
> > unreachable code that could cause potential bugs. There is no plan to
> > enable it by default.
> >
> > The following code was detected as unreachable:
> >
> > fs/ext4/namei.c:831:17: warning: code will never be executed
> > [-Wunreachable-code]
> > unsigned n = count - 1;
> > ^~~~~
> > fs/ext4/namei.c:830:7: note: silence by adding parentheses to mark code as
> > explicitly dead
> > if (0) { // linear search cross check
> > ^
> > /* DISABLES CODE */ ( )
> >
> > This has been present since commit ac27a0ec112a ("[PATCH] ext4: initial
> > copy of files from ext3") and fs/ext3 had it present at the beginning of
> > git history. It has not been changed since.
> >
> > This patch moves the code to a new function `htree_rep_invariant_check`
> > which only performs the check when DX_DEBUG is set. This allows the
> > function to be used in other parts of the code.
> >
> > Suggestions from: Andreas, Christoph, Nathan, Nick and Ted.
> >
> > Signed-off-by: Vinicius Tinti <viniciustinti@xxxxxxxxx>
>
> Thanks, applied, although I rewrote the commit description:
>
> ext4: factor out htree rep invariant check
>
> This patch moves some debugging code which is used to validate the
> hash tree node when doing a binary search of an htree node into a
> separate function, which is disabled by default (since it is only used
> by developers when they are modifying the htree code paths).
>
> In addition to cleaning up the code to make it more maintainable, it
> silences a Clang compiler warning when -Wunreachable-code-aggressive
> is enabled. (There is no plan to enable this warning by default, since
> there it has far too many false positives; nevertheless, this commit
> reduces one of the many false positives by one.)
>
> The original description buried the lede, in terms of the primary
> reason why I think the change was worthwhile (although I know you have
> different priorities than mine :-).
>
> Thanks for working to find a way to improve the code in a way that
> makes both of us happy!
Thanks for the feedback.
And thanks for all the ones who reviewed.
> - Ted
