On Fri, Dec 13, 2019 at 03:03:11PM -0800, Randy Dunlap wrote: > On 12/12/19 12:25 PM, Randy Dunlap wrote: > > On 12/12/19 10:47 AM, Josh Poimboeuf wrote: > >> On Wed, Dec 11, 2019 at 08:21:38AM -0800, Randy Dunlap wrote: > >>> [oops, forgot to add Josh and PeterZ] > >>> > >>> On 12/11/19 5:49 AM, David Sterba wrote: > >>>> On Fri, Dec 06, 2019 at 08:17:30AM -0800, Randy Dunlap wrote: > >>>>> On 12/5/19 6:54 PM, Stephen Rothwell wrote: > >>>>>> Hi all, > >>>>>> > >>>>>> Please do not add any material for v5.6 to your linux-next included > >>>>>> trees until after v5.5-rc1 has been released. > >>>>>> > >>>>>> Changes since 20191204: > >>>>>> > >>>>> > >>>>> on x86_64: > >>>>> > >>>>> fs/btrfs/ctree.o: warning: objtool: btrfs_search_slot()+0x2d4: unreachable instruction > >>>> > >>>> Can somebody enlighten me what is one supposed to do to address the > >>>> warnings? Function names reported in the list contain our ASSERT macro > >>>> that conditionally calls BUG() that I believe is what could cause the > >>>> unreachable instructions but I don't see how. > >>>> > >>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/btrfs/ctree.h#n3113 > >>>> > >>>> __cold > >>>> static inline void assfail(const char *expr, const char *file, int line) > >>>> { > >>>> if (IS_ENABLED(CONFIG_BTRFS_ASSERT)) { > >>>> pr_err("assertion failed: %s, in %s:%d\n", expr, file, line); > >>>> BUG(); > >>>> } > >>>> } > >>>> > >>>> #define ASSERT(expr) \ > >>>> (likely(expr) ? (void)0 : assfail(#expr, __FILE__, __LINE__)) > >>>> > >> > >> Randy, can you share one of the btrfs .o files? I'm not able to > >> recreate. > >> > > > > Hm. I'll have to try to recreate this. I no longer have files from 20191206 > > (lack of space). > > > > I'll let you know if/when I can recreate it. > > OK, 40 builds later, I have reproduced it. > > I am attaching one of the btrfs .o files and the kernel config file (FTR). > (gzipped) > Let me know if you want more of the .o files. Thanks. This is arguably a compiler bug, but the below produces better code generation by adding a noreturn annotation. I think GCC gets tripped up by the IS_ENABLED conditional and can't always tell that assfail (sic) doesn't return. BTW, I'm on my way out the door for a week of much-needed PTO but I can handle this patch (and several others I have pending which were reported by you) when I get back. diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index b2e8fd8a8e59..bbd68520f5f1 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -3110,14 +3110,16 @@ do { \ rcu_read_unlock(); \ } while (0) -__cold +#ifdef CONFIG_BTRFS_ASSERT +__cold __unlikely static inline void assfail(const char *expr, const char *file, int line) { - if (IS_ENABLED(CONFIG_BTRFS_ASSERT)) { - pr_err("assertion failed: %s, in %s:%d\n", expr, file, line); - BUG(); - } + pr_err("assertion failed: %s, in %s:%d\n", expr, file, line); + BUG(); } +#else +static inline void assfail(const char *expr, const char *file, int line) {} +#endif #define ASSERT(expr) \ (likely(expr) ? (void)0 : assfail(#expr, __FILE__, __LINE__))
