* Re: [PATCH next v2 1/2] dump_stack: move cpu lock to printk.c [not found] <20210607200232.22211-2-john.ogness@linutronix.de> @ 2021-06-08 2:43 ` kernel test robot 2021-06-08 13:48 ` Petr Mladek 0 siblings, 1 reply; 3+ messages in thread From: kernel test robot @ 2021-06-08 2:43 UTC (permalink / raw) To: John Ogness, Petr Mladek Cc: kbuild-all, Sergey Senozhatsky, Steven Rostedt, Thomas Gleixner, linux-kernel, Andrew Morton, Linux Memory Management List, Dmitry Safonov, Peter Zijlstra, Marco Elver [-- Attachment #1: Type: text/plain, Size: 2245 bytes --] 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); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ vim +/lock_flag +107 lib/dump_stack.c 90 91 /** 92 * dump_stack - dump the current task information and its stack trace 93 * 94 * Architectures can override this implementation by implementing its own. 95 */ 96 asmlinkage __visible void dump_stack_lvl(const char *log_lvl) 97 { 98 unsigned long irq_flags; 99 bool lock_flag; 100 101 /* 102 * Permit this cpu to perform nested stack dumps while serialising 103 * against other CPUs 104 */ 105 printk_cpu_lock_irqsave(&lock_flag, &irq_flags); 106 __dump_stack(log_lvl); > 107 printk_cpu_unlock_irqrestore(lock_flag, irq_flags); 108 } 109 EXPORT_SYMBOL(dump_stack_lvl); 110 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org [-- Attachment #2: .config.gz --] [-- Type: application/gzip, Size: 26602 bytes --] ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH next v2 1/2] dump_stack: move cpu lock to printk.c 2021-06-08 2:43 ` [PATCH next v2 1/2] dump_stack: move cpu lock to printk.c kernel test robot @ 2021-06-08 13:48 ` Petr Mladek 2021-06-10 13:26 ` John Ogness 0 siblings, 1 reply; 3+ messages in thread From: Petr Mladek @ 2021-06-08 13:48 UTC (permalink / raw) To: kernel test robot Cc: John Ogness, kbuild-all, Sergey Senozhatsky, Steven Rostedt, Thomas Gleixner, linux-kernel, Andrew Morton, Linux Memory Management List, Dmitry Safonov, Peter Zijlstra, Marco Elver 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 ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH next v2 1/2] dump_stack: move cpu lock to printk.c 2021-06-08 13:48 ` Petr Mladek @ 2021-06-10 13:26 ` John Ogness 0 siblings, 0 replies; 3+ messages in thread From: John Ogness @ 2021-06-10 13:26 UTC (permalink / raw) To: Petr Mladek, kernel test robot Cc: kbuild-all, Sergey Senozhatsky, Steven Rostedt, Thomas Gleixner, linux-kernel, Andrew Morton, Linux Memory Management List, Dmitry Safonov, Peter Zijlstra, Marco Elver On 2021-06-08, Petr Mladek <pmladek@suse.com> wrote: >> 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. Strangely enough, if I set a value for @lock_flag, it is happy and does not complain about @irq_flags. Probably a compiler oversight. > Anyway, we will likely need to do some trickery via #define to tell > the compiler that the value is set. This is on ARCH=mips and !CONFIG_SMP. So the value is _not_ getting set. (The static inline function does nothing.) By changing printk_cpu_unlock_irqrestore() to use pointers: static inline void printk_cpu_unlock_irqrestore(bool *lock_flag, unsigned long *irq_flags) then the warning disappears. Indeed, by not using pointers on unlock, technically data is copied that was never initialized. I thought maybe the compiler would optimize all that out, but it seems that it does not. I have no problems using pointers for unlock(). It was strange using pointers for lock(), but not for unlock() anyway. Or would you prefer something else? John Ogness ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-06-10 13:26 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <20210607200232.22211-2-john.ogness@linutronix.de> 2021-06-08 2:43 ` [PATCH next v2 1/2] dump_stack: move cpu lock to printk.c kernel test robot 2021-06-08 13:48 ` Petr Mladek 2021-06-10 13:26 ` John Ogness
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