On Wed, Sep 13, 2023 at 06:01:42PM -0700, Kees Cook wrote:
> > +++ 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?)
Sure, see below.
BTW, I'm about to go off grid for 1.5 weeks, so there will be no v3
coming from me anytime soon :-)
---8<---
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Subject: [PATCH v2] 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 WARN_ON(1) 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 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 | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/bcachefs/buckets.h b/fs/bcachefs/buckets.h
index f192809f50cf..211f054bf83d 100644
--- a/fs/bcachefs/buckets.h
+++ b/fs/bcachefs/buckets.h
@@ -180,7 +180,8 @@ static inline u64 bch2_dev_buckets_reserved(struct bch_dev *ca, enum bch_waterma
switch (watermark) {
case BCH_WATERMARK_NR:
- unreachable();
+ WARN_ON(1);
+ break;
case BCH_WATERMARK_stripe:
reserved += ca->mi.nbuckets >> 6;
fallthrough;
--
2.41.0
