Messages in this thread | | | Date | Mon, 25 Mar 2019 14:13:05 +0100 | From | David Sterba <> | Subject | Re: [PATCH] btrfs: use BUG() instead of BUG_ON(1) |
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On Mon, Mar 25, 2019 at 03:06:12PM +0200, Nikolay Borisov wrote: > > > On 25.03.19 г. 15:02 ч., Arnd Bergmann wrote: > > BUG_ON(1) leads to bogus warnings from clang when > > CONFIG_PROFILE_ANNOTATED_BRANCHES is set: > > > > fs/btrfs/volumes.c:5041:3: error: variable 'max_chunk_size' is used uninitialized whenever 'if' condition is false > > [-Werror,-Wsometimes-uninitialized] > > BUG_ON(1); > > ^~~~~~~~~ > > include/asm-generic/bug.h:61:36: note: expanded from macro 'BUG_ON' > > #define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0) > > ^~~~~~~~~~~~~~~~~~~ > > include/linux/compiler.h:48:23: note: expanded from macro 'unlikely' > > # define unlikely(x) (__branch_check__(x, 0, __builtin_constant_p(x))) > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > fs/btrfs/volumes.c:5046:9: note: uninitialized use occurs here > > max_chunk_size); > > ^~~~~~~~~~~~~~ > > include/linux/kernel.h:860:36: note: expanded from macro 'min' > > #define min(x, y) __careful_cmp(x, y, <) > > ^ > > include/linux/kernel.h:853:17: note: expanded from macro '__careful_cmp' > > __cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op)) > > ^ > > include/linux/kernel.h:847:25: note: expanded from macro '__cmp_once' > > typeof(y) unique_y = (y); \ > > ^ > > fs/btrfs/volumes.c:5041:3: note: remove the 'if' if its condition is always true > > BUG_ON(1); > > ^ > > include/asm-generic/bug.h:61:32: note: expanded from macro 'BUG_ON' > > #define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0) > > ^ > > fs/btrfs/volumes.c:4993:20: note: initialize the variable 'max_chunk_size' to silence this warning > > u64 max_chunk_size; > > ^ > > = 0 > > > > Change it to BUG() so clang can see that this code path can never > > continue. > > Long-term we have to eliminate to bug_on's but until then:
I think in those places it's "this must never happen", so it's not the the typical example of BUG_ON misuse we want to eliminate. Fixing the compiler waring is ok though.
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