linux-kernel - Re: linux-next: Tree for Sep 12 (bcachefs, objtool)

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Message-ID: <20230913210829.zkxv6qqlamymhatr@treble>
Date:   Wed, 13 Sep 2023 23:08:29 +0200
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: linux-next: Tree for Sep 12 (bcachefs, objtool)

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@...nel.org>
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@...radead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 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();
 	case BCH_WATERMARK_stripe:
 		reserved += ca->mi.nbuckets >> 6;
 		fallthrough;
-- 
2.41.0