Re: [PATCH v2 15/18] btrfs: disk-io: introduce subpage metadata validation check

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2020/12/14 下午7:17, Nikolay Borisov wrote:
>
>
> On 14.12.20 г. 12:50 ч., Qu Wenruo wrote:
>>
>> IIRC ASSERT() won't execute whatever in it for non debug build.
>> Thus ASSERT(atomic_*) would cause non-debug kernel not to decrease the
>> io_pages and hangs the system.
>
> Nope:
>
>    3362 #ifdef CONFIG_BTRFS_ASSERT
>       1 __cold __noreturn
>       2 static inline void assertfail(const char *expr, const char *file, int line)
>       3 {
>       4         pr_err("assertion failed: %s, in %s:%d\n", expr, file, line);
>       5         BUG();
>       6 }
>       7
>       8 #define ASSERT(expr)                                            \
>       9         (likely(expr) ? (void)0 : assertfail(#expr, __FILE__, __LINE__))
>      10
>      11 #else
>      12 static inline void assertfail(const char *expr, const char* file, int line) { }
>      13 #define ASSERT(expr)    (void)(expr)               <-- expression is evaluated.
>      14 #endif
>
Wow, that's too tricky and maybe that's the reason why Josef is
complaining about the ASSERT()s slows down the system.

In fact, from the assert(3) man page, we're doing things differently
than user space at least:

   If the macro NDEBUG is defined at the moment <assert.h> was last
   included, the macro assert() generates no code, and hence does nothing
   at all.

So I'm confused, what's the proper way to do ASSERT()?

Thanks,
Qu