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SubjectRe: [PATCH next v2 1/2] dump_stack: move cpu lock to printk.c
On Tue 2021-06-08 10:43:46, kernel test robot wrote:
> Hi John,
>
> I love your patch! Perhaps something to improve:
>
> [auto build test WARNING on next-20210607]
>
> url: https://github.com/0day-ci/linux/commits/John-Ogness/introduce-printk-cpu-lock/20210608-040454
> base: 7f09e895a7f3e0af63bf9ec6c7c22893ec7e6c8e
> config: mips-randconfig-r036-20210607 (attached as .config)
> compiler: mips-linux-gcc (GCC) 9.3.0
> reproduce (this is a W=1 build):
> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> chmod +x ~/bin/make.cross
> # https://github.com/0day-ci/linux/commit/136bcc2980e636b2ae156ca63fbe95c713e44c1b
> git remote add linux-review https://github.com/0day-ci/linux
> git fetch --no-tags linux-review John-Ogness/introduce-printk-cpu-lock/20210608-040454
> git checkout 136bcc2980e636b2ae156ca63fbe95c713e44c1b
> # save the attached .config to linux build tree
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=mips
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All warnings (new ones prefixed by >>):
>
> lib/dump_stack.c: In function 'dump_stack_lvl':
> >> lib/dump_stack.c:107:2: warning: 'lock_flag' is used uninitialized in this function [-Wuninitialized]
> 107 | printk_cpu_unlock_irqrestore(lock_flag, irq_flags);
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Interesting. I am curious that it does not complain also about
irq_flags. But it is possible the it reports only the first problem.

Anyway, we will likely need to do some trickery via #define to tell
the compiler that the value is set. I mean to do similar thing as:

#define raw_local_irq_save(flags) \
do { \
typecheck(unsigned long, flags); \
flags = arch_local_irq_save(); \
} while (0)


In our case, it might look like:

#define printk_cpu_lock_irqsave(lock_nested, irq_flags) \
do { \
local_irq_save(irq_flags); \
typecheck(bool, lock_nested); \
lock_nested = __printk_cpu_lock(irq_flags); \
} while (0)


then we would need to do in __prink_cpu_lock(unsigned long irq_flags)


} else {
local_irq_restore(irq_flags);

/*
* Wait for the lock to release before jumping to cmpxchg()
* in order to mitigate the thundering herd problem.
*/
do {
cpu_relax();
} while (atomic_read(&printk_cpulock_owner) != -1);

local_irq_save(irq_flags)
goto retry;
}

Best Regards,
Petr

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