James,

If I understand correctly, you're saying you want to be able to build without 
debug support...?  I'm not convinced that building a client without debug 
support is interesting or useful.  In fact, I think it would be harmful, and we 
shouldn't open up the possibility - this is switchable debug with very low 
overhead when not actually "on".  It would be really awful to get a problem on 
a running system and discover there's no debug support - that you can't even 
enable debug without a reinstall.

If I've understood you correctly, then I would want to see proof of a 
significant performance cost when debug is built but *off* before agreeing to 
even exposing this option.  (I know it's a choice they'd have to make, but if 
it's not really useful with a side order of potentially harmful, we shouldn't 
even give people the choice.)

- Patrick

´╗┐On 4/15/18, 10:49 PM, "lustre-devel on behalf of James Simmons" 
<lustre-devel-boun...@lists.lustre.org on behalf of jsimm...@infradead.org> 
wrote:

    
    > CDEBUG_STACK() and CHECK_STACK() are macros to help with
    > debugging, so move them from
    >    drivers/staging/lustre/include/linux/libcfs/linux/libcfs.h
    > to
    >    drivers/staging/lustre/include/linux/libcfs/libcfs_debug.h
    > 
    > This seems a more fitting location, and is a step towards
    > removing linux/libcfs.h and simplifying the include file structure.
    
    Nak. Currently the lustre client always enables debugging but that
    shouldn't be the case. What we do need is the able to turn off the 
    crazy debugging stuff. In the development branch of lustre it is
    done with CDEBUG_ENABLED. We need something like that in Kconfig
    much like we have CONFIG_LUSTRE_DEBUG_EXPENSIVE_CHECK. Since we like
    to be able to turn that off this should be moved to just after
    LIBCFS_DEBUG_MSG_DATA_DECL. Then from CHECK_STACK down to CWARN()
    it can be build out. When CDEBUG_ENABLED is disabled CDEBUG_LIMIT
    would be empty.
     
    > Signed-off-by: NeilBrown <ne...@suse.com>
    > ---
    >  .../lustre/include/linux/libcfs/libcfs_debug.h     |   32 
++++++++++++++++++++
    >  .../lustre/include/linux/libcfs/linux/libcfs.h     |   31 
-------------------
    >  2 files changed, 32 insertions(+), 31 deletions(-)
    > 
    > diff --git a/drivers/staging/lustre/include/linux/libcfs/libcfs_debug.h 
b/drivers/staging/lustre/include/linux/libcfs/libcfs_debug.h
    > index 9290a19429e7..0dc7b91efe7c 100644
    > --- a/drivers/staging/lustre/include/linux/libcfs/libcfs_debug.h
    > +++ b/drivers/staging/lustre/include/linux/libcfs/libcfs_debug.h
    > @@ -62,6 +62,38 @@ int libcfs_debug_str2mask(int *mask, const char *str, 
int is_subsys);
    >  extern unsigned int libcfs_catastrophe;
    >  extern unsigned int libcfs_panic_on_lbug;
    >  
    > +/* Enable debug-checks on stack size - except on x86_64 */
    > +#if !defined(__x86_64__)
    > +# ifdef __ia64__
    > +#  define CDEBUG_STACK() (THREAD_SIZE -                           \
    > +                   ((unsigned long)__builtin_dwarf_cfa() &       \
    > +                    (THREAD_SIZE - 1)))
    > +# else
    > +#  define CDEBUG_STACK() (THREAD_SIZE -                           \
    > +                   ((unsigned long)__builtin_frame_address(0) &  \
    > +                    (THREAD_SIZE - 1)))
    > +# endif /* __ia64__ */
    > +
    > +#define __CHECK_STACK(msgdata, mask, cdls)                             \
    > +do {                                                                 \
    > + if (unlikely(CDEBUG_STACK() > libcfs_stack)) {            \
    > +         LIBCFS_DEBUG_MSG_DATA_INIT(msgdata, D_WARNING, NULL);   \
    > +         libcfs_stack = CDEBUG_STACK();                    \
    > +         libcfs_debug_msg(msgdata,                              \
    > +                          "maximum lustre stack %lu\n",    \
    > +                          CDEBUG_STACK());                      \
    > +         (msgdata)->msg_mask = mask;                          \
    > +         (msgdata)->msg_cdls = cdls;                          \
    > +         dump_stack();                                      \
    > +       /*panic("LBUG");*/                                        \
    > + }                                                              \
    > +} while (0)
    > +#define CFS_CHECK_STACK(msgdata, mask, cdls)  __CHECK_STACK(msgdata, 
mask, cdls)
    > +#else /* __x86_64__ */
    > +#define CFS_CHECK_STACK(msgdata, mask, cdls) do {} while (0)
    > +#define CDEBUG_STACK() (0L)
    > +#endif /* __x86_64__ */
    > +
    >  #ifndef DEBUG_SUBSYSTEM
    >  # define DEBUG_SUBSYSTEM S_UNDEFINED
    >  #endif
    > diff --git a/drivers/staging/lustre/include/linux/libcfs/linux/libcfs.h 
b/drivers/staging/lustre/include/linux/libcfs/linux/libcfs.h
    > index 07d3cb2217d1..83aec9c7698f 100644
    > --- a/drivers/staging/lustre/include/linux/libcfs/linux/libcfs.h
    > +++ b/drivers/staging/lustre/include/linux/libcfs/linux/libcfs.h
    > @@ -80,35 +80,4 @@
    >  #include <stdarg.h>
    >  #include "linux-cpu.h"
    >  
    > -#if !defined(__x86_64__)
    > -# ifdef __ia64__
    > -#  define CDEBUG_STACK() (THREAD_SIZE -                           \
    > -                   ((unsigned long)__builtin_dwarf_cfa() &       \
    > -                    (THREAD_SIZE - 1)))
    > -# else
    > -#  define CDEBUG_STACK() (THREAD_SIZE -                           \
    > -                   ((unsigned long)__builtin_frame_address(0) &  \
    > -                    (THREAD_SIZE - 1)))
    > -# endif /* __ia64__ */
    > -
    > -#define __CHECK_STACK(msgdata, mask, cdls)                             \
    > -do {                                                                 \
    > - if (unlikely(CDEBUG_STACK() > libcfs_stack)) {            \
    > -         LIBCFS_DEBUG_MSG_DATA_INIT(msgdata, D_WARNING, NULL);   \
    > -         libcfs_stack = CDEBUG_STACK();                    \
    > -         libcfs_debug_msg(msgdata,                              \
    > -                          "maximum lustre stack %lu\n",    \
    > -                          CDEBUG_STACK());                      \
    > -         (msgdata)->msg_mask = mask;                          \
    > -         (msgdata)->msg_cdls = cdls;                          \
    > -         dump_stack();                                      \
    > -       /*panic("LBUG");*/                                        \
    > - }                                                              \
    > -} while (0)
    > -#define CFS_CHECK_STACK(msgdata, mask, cdls)  __CHECK_STACK(msgdata, 
mask, cdls)
    > -#else /* __x86_64__ */
    > -#define CFS_CHECK_STACK(msgdata, mask, cdls) do {} while (0)
    > -#define CDEBUG_STACK() (0L)
    > -#endif /* __x86_64__ */
    > -
    >  #endif /* _LINUX_LIBCFS_H */
    > 
    > 
    > 
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