Re: [PATCH v2 01/10] riscv: Implement cmpxchg32/64() using Zacas

[kernel test robot <lkp@intel.com>]

Hi Alexandre,

kernel test robot noticed the following build errors:

[auto build test ERROR on soc/for-next]
[also build test ERROR on linus/master v6.10-rc6 next-20240703]
[cannot apply to arnd-asm-generic/master robh/for-next tip/locking/core]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Alexandre-Ghiti/riscv-Implement-cmpxchg32-64-using-Zacas/20240627-034946
base:   https://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git for-next
patch link:    https://lore.kernel.org/r/20240626130347.520750-2-alexghiti%40rivosinc.com
patch subject: [PATCH v2 01/10] riscv: Implement cmpxchg32/64() using Zacas
config: riscv-randconfig-002-20240704 (https://download.01.org/0day-ci/archive/20240704/202407041157.odTZAYZ6-lkp@intel.com/config)
compiler: clang version 16.0.6 (https://github.com/llvm/llvm-project 7cbf1a2591520c2491aa35339f227775f4d3adf6)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240704/202407041157.odTZAYZ6-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202407041157.odTZAYZ6-lkp@intel.com/

All errors (new ones prefixed by >>):

>> kernel/sched/core.c:11873:7: error: cannot jump from this asm goto statement to one of its possible targets
                   if (try_cmpxchg(&pcpu_cid->cid, &lazy_cid, MM_CID_UNSET))
                       ^
   include/linux/atomic/atomic-instrumented.h:4880:2: note: expanded from macro 'try_cmpxchg'
           raw_try_cmpxchg(__ai_ptr, __ai_oldp, __VA_ARGS__); \
           ^
   include/linux/atomic/atomic-arch-fallback.h:192:9: note: expanded from macro 'raw_try_cmpxchg'
           ___r = raw_cmpxchg((_ptr), ___o, (_new)); \
                  ^
   include/linux/atomic/atomic-arch-fallback.h:55:21: note: expanded from macro 'raw_cmpxchg'
   #define raw_cmpxchg arch_cmpxchg
                       ^
   arch/riscv/include/asm/cmpxchg.h:212:2: note: expanded from macro 'arch_cmpxchg'
           _arch_cmpxchg((ptr), (o), (n), ".rl", "", "     fence rw, rw\n")
           ^
   arch/riscv/include/asm/cmpxchg.h:189:3: note: expanded from macro '_arch_cmpxchg'
                   __arch_cmpxchg(".w", ".w" sc_sfx, prepend, append,      \
                   ^
   arch/riscv/include/asm/cmpxchg.h:144:3: note: expanded from macro '__arch_cmpxchg'
                   asm goto(ALTERNATIVE("nop", "j %[zacas]", 0,            \
                   ^
   kernel/sched/core.c:11840:7: note: possible target of asm goto statement
           if (!try_cmpxchg(&pcpu_cid->cid, &cid, lazy_cid))
                ^
   include/linux/atomic/atomic-instrumented.h:4880:2: note: expanded from macro 'try_cmpxchg'
           raw_try_cmpxchg(__ai_ptr, __ai_oldp, __VA_ARGS__); \
           ^
   include/linux/atomic/atomic-arch-fallback.h:192:9: note: expanded from macro 'raw_try_cmpxchg'
           ___r = raw_cmpxchg((_ptr), ___o, (_new)); \
                  ^
   include/linux/atomic/atomic-arch-fallback.h:55:21: note: expanded from macro 'raw_cmpxchg'
   #define raw_cmpxchg arch_cmpxchg
                       ^
   arch/riscv/include/asm/cmpxchg.h:212:2: note: expanded from macro 'arch_cmpxchg'
           _arch_cmpxchg((ptr), (o), (n), ".rl", "", "     fence rw, rw\n")
           ^
   arch/riscv/include/asm/cmpxchg.h:189:3: note: expanded from macro '_arch_cmpxchg'
                   __arch_cmpxchg(".w", ".w" sc_sfx, prepend, append,      \
                   ^
   arch/riscv/include/asm/cmpxchg.h:161:10: note: expanded from macro '__arch_cmpxchg'
                                                                           \
                                                                           ^
   kernel/sched/core.c:11872:2: note: jump exits scope of variable with __attribute__((cleanup))
           scoped_guard (irqsave) {
           ^
   include/linux/cleanup.h:169:20: note: expanded from macro 'scoped_guard'
           for (CLASS(_name, scope)(args),                                 \
                             ^
   kernel/sched/core.c:11840:7: error: cannot jump from this asm goto statement to one of its possible targets
           if (!try_cmpxchg(&pcpu_cid->cid, &cid, lazy_cid))
                ^
   include/linux/atomic/atomic-instrumented.h:4880:2: note: expanded from macro 'try_cmpxchg'
           raw_try_cmpxchg(__ai_ptr, __ai_oldp, __VA_ARGS__); \
           ^
   include/linux/atomic/atomic-arch-fallback.h:192:9: note: expanded from macro 'raw_try_cmpxchg'
           ___r = raw_cmpxchg((_ptr), ___o, (_new)); \
                  ^
   include/linux/atomic/atomic-arch-fallback.h:55:21: note: expanded from macro 'raw_cmpxchg'
   #define raw_cmpxchg arch_cmpxchg
                       ^
   arch/riscv/include/asm/cmpxchg.h:212:2: note: expanded from macro 'arch_cmpxchg'
           _arch_cmpxchg((ptr), (o), (n), ".rl", "", "     fence rw, rw\n")
           ^
   arch/riscv/include/asm/cmpxchg.h:189:3: note: expanded from macro '_arch_cmpxchg'
                   __arch_cmpxchg(".w", ".w" sc_sfx, prepend, append,      \
                   ^
   arch/riscv/include/asm/cmpxchg.h:144:3: note: expanded from macro '__arch_cmpxchg'
                   asm goto(ALTERNATIVE("nop", "j %[zacas]", 0,            \
                   ^
   kernel/sched/core.c:11873:7: note: possible target of asm goto statement
                   if (try_cmpxchg(&pcpu_cid->cid, &lazy_cid, MM_CID_UNSET))
                       ^
   include/linux/atomic/atomic-instrumented.h:4880:2: note: expanded from macro 'try_cmpxchg'
           raw_try_cmpxchg(__ai_ptr, __ai_oldp, __VA_ARGS__); \
           ^
   include/linux/atomic/atomic-arch-fallback.h:192:9: note: expanded from macro 'raw_try_cmpxchg'
           ___r = raw_cmpxchg((_ptr), ___o, (_new)); \
                  ^
   include/linux/atomic/atomic-arch-fallback.h:55:21: note: expanded from macro 'raw_cmpxchg'
   #define raw_cmpxchg arch_cmpxchg
                       ^
   arch/riscv/include/asm/cmpxchg.h:212:2: note: expanded from macro 'arch_cmpxchg'
           _arch_cmpxchg((ptr), (o), (n), ".rl", "", "     fence rw, rw\n")
           ^
   arch/riscv/include/asm/cmpxchg.h:189:3: note: expanded from macro '_arch_cmpxchg'
                   __arch_cmpxchg(".w", ".w" sc_sfx, prepend, append,      \
                   ^
   arch/riscv/include/asm/cmpxchg.h:161:10: note: expanded from macro '__arch_cmpxchg'
                                                                           \
                                                                           ^
   kernel/sched/core.c:11872:2: note: jump bypasses initialization of variable with __attribute__((cleanup))
           scoped_guard (irqsave) {
           ^
   include/linux/cleanup.h:169:20: note: expanded from macro 'scoped_guard'
           for (CLASS(_name, scope)(args),                                 \
                             ^
   2 errors generated.


vim +11873 kernel/sched/core.c

223baf9d17f25e Mathieu Desnoyers 2023-04-20  11821  
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11822  static void sched_mm_cid_remote_clear(struct mm_struct *mm, struct mm_cid *pcpu_cid,
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11823  				      int cpu)
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11824  {
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11825  	struct rq *rq = cpu_rq(cpu);
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11826  	struct task_struct *t;
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11827  	int cid, lazy_cid;
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11828  
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11829  	cid = READ_ONCE(pcpu_cid->cid);
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11830  	if (!mm_cid_is_valid(cid))
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11831  		return;
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11832  
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11833  	/*
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11834  	 * Clear the cpu cid if it is set to keep cid allocation compact.  If
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11835  	 * there happens to be other tasks left on the source cpu using this
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11836  	 * mm, the next task using this mm will reallocate its cid on context
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11837  	 * switch.
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11838  	 */
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11839  	lazy_cid = mm_cid_set_lazy_put(cid);
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11840  	if (!try_cmpxchg(&pcpu_cid->cid, &cid, lazy_cid))
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11841  		return;
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11842  
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11843  	/*
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11844  	 * The implicit barrier after cmpxchg per-mm/cpu cid before loading
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11845  	 * rq->curr->mm matches the scheduler barrier in context_switch()
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11846  	 * between store to rq->curr and load of prev and next task's
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11847  	 * per-mm/cpu cid.
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11848  	 *
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11849  	 * The implicit barrier after cmpxchg per-mm/cpu cid before loading
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11850  	 * rq->curr->mm_cid_active matches the barrier in
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11851  	 * sched_mm_cid_exit_signals(), sched_mm_cid_before_execve(), and
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11852  	 * sched_mm_cid_after_execve() between store to t->mm_cid_active and
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11853  	 * load of per-mm/cpu cid.
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11854  	 */
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11855  
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11856  	/*
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11857  	 * If we observe an active task using the mm on this rq after setting
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11858  	 * the lazy-put flag, that task will be responsible for transitioning
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11859  	 * from lazy-put flag set to MM_CID_UNSET.
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11860  	 */
0e34600ac9317d Peter Zijlstra    2023-06-09  11861  	scoped_guard (rcu) {
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11862  		t = rcu_dereference(rq->curr);
0e34600ac9317d Peter Zijlstra    2023-06-09  11863  		if (READ_ONCE(t->mm_cid_active) && t->mm == mm)
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11864  			return;
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11865  	}
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11866  
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11867  	/*
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11868  	 * The cid is unused, so it can be unset.
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11869  	 * Disable interrupts to keep the window of cid ownership without rq
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11870  	 * lock small.
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11871  	 */
0e34600ac9317d Peter Zijlstra    2023-06-09  11872  	scoped_guard (irqsave) {
223baf9d17f25e Mathieu Desnoyers 2023-04-20 @11873  		if (try_cmpxchg(&pcpu_cid->cid, &lazy_cid, MM_CID_UNSET))
223baf9d17f25e Mathieu Desnoyers 2023-04-20  11874  			__mm_cid_put(mm, cid);
0e34600ac9317d Peter Zijlstra    2023-06-09  11875  	}
af7f588d8f7355 Mathieu Desnoyers 2022-11-22  11876  }
af7f588d8f7355 Mathieu Desnoyers 2022-11-22  11877  

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