[PATCH] seqlock: Allow UBSAN to fail optimizing

[Peter Zijlstra <peterz@infradead.org>]

Very similar to commit:

  b94d45b6bbb4 ("seqlock: Allow KASAN to fail optimizing")

mark UBSAN as failing to optimize and not suitable for release builds.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202601290910.uwScjRjc-lkp@intel.com/
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123873
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---

Debian folks, can you please remove CONFIG_UBSAN=y from your builds,
this is, per GCC devs, not a feature suitable for production!

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index c00063dffba3..436f05bf5dd7 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -1259,14 +1259,14 @@ static __always_inline void __scoped_seqlock_cleanup(struct ss_tmp *sst)
 
 extern void __scoped_seqlock_invalid_target(void);
 
-#if (defined(CONFIG_CC_IS_GCC) && CONFIG_GCC_VERSION < 90000) || defined(CONFIG_KASAN)
+#if (defined(CONFIG_CC_IS_GCC) && CONFIG_GCC_VERSION < 90000) || defined(CONFIG_KASAN) || defined(CONFIG_UBSAN)
 /*
  * For some reason some GCC-8 architectures (nios2, alpha) have trouble
  * determining that the ss_done state is impossible in __scoped_seqlock_next()
  * below.
  *
- * Similarly KASAN is known to confuse compilers enough to break this. But we
- * don't care about code quality for KASAN builds anyway.
+ * Similarly *SAN is known to confuse compilers enough to break this. But we
+ * don't care about code quality for *SAN builds anyway.
  */
 static inline void __scoped_seqlock_bug(void) { }
 #else