On Wed, Sep 13, 2023 at 11:08:29PM +0200, Josh Poimboeuf wrote:
> On Tue, Sep 12, 2023 at 04:36:55PM -0700, Randy Dunlap wrote:
> >
> >
> > On 9/11/23 22:26, Stephen Rothwell wrote:
> > > Hi all,
> > >
> > > Changes since 20230911:
> > >
> > > New tree: bcachefs
> > >
> > > The bcachefs tree gained a semantic conflict against Linus' tree for
> > > which I applied a patch.
> > >
> > > The wireless-next tree gaind a conflict against the wireless tree.
> > >
> > > Non-merge commits (relative to Linus' tree): 4095
> > > 1552 files changed, 346893 insertions(+), 22945 deletions(-)
> > >
> > > ----------------------------------------------------------------------------
> >
> > on x86_64:
> >
> > vmlinux.o: warning: objtool: bch2_dev_buckets_reserved.part.0() is missing an ELF size annotation
>
> Here ya go:
>
> ---8<---
>
> From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Subject: [PATCH] bcachefs: Remove undefined behavior in bch2_dev_buckets_reserved()
>
> In general it's a good idea to avoid using bare unreachable() because it
> introduces undefined behavior in compiled code. In this case it even
> confuses GCC into emitting an empty unused
> bch2_dev_buckets_reserved.part.0() function.
>
> Use BUG() instead, which is nice and defined. While in theory it should
> never trigger, if something were to go awry and the BCH_WATERMARK_NR
> case were to actually hit, the failure mode is much more robust.
>
> Fixes the following warnings:
>
> vmlinux.o: warning: objtool: bch2_bucket_alloc_trans() falls through to next function bch2_reset_alloc_cursors()
> vmlinux.o: warning: objtool: bch2_dev_buckets_reserved.part.0() is missing an ELF size annotation
>
> Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> ---
> fs/bcachefs/buckets.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/bcachefs/buckets.h b/fs/bcachefs/buckets.h
> index f192809f50cf..0eff05c79c65 100644
> --- a/fs/bcachefs/buckets.h
> +++ b/fs/bcachefs/buckets.h
> @@ -180,7 +180,7 @@ static inline u64 bch2_dev_buckets_reserved(struct bch_dev *ca, enum bch_waterma
>
> switch (watermark) {
> case BCH_WATERMARK_NR:
> - unreachable();
> + BUG();
Linus gets really upset about new BUG() usage (takes out the entire
system):
https://docs.kernel.org/process/deprecated.html#bug-and-bug-on
It'd be nicer to actually handle the impossible case. (WARN and return
0?)
-Kees
> case BCH_WATERMARK_stripe:
> reserved += ca->mi.nbuckets >> 6;
> fallthrough;
> --
> 2.41.0
>
--
Kees Cook
