Re: [PATCH 1/1] mm/vmalloc: Add preempt point in purge_vmap_node() when enabling kasan

[Uladzislau Rezki <urezki@gmail.com>]

On Mon, Jul 22, 2024 at 07:50:54PM +0800, Adrian Huang wrote:
> > I tried to simulate the reported splat and i can reproduce it with KASAN
> > enabled. I use qemu on my 64-core system, it allows me to specify 255
> > cores while running VM. The kernel is 6.10.0-rc5.
> >
> > The kernel should be built with CONFIG_KASAN=y and CONFIG_KASAN_VMALLOC=y
> >
> > The "soft lockup" can be triggered when the kernel is compiled within a
> > VM using 256 jobs and preemption is disabled:
> >
> > echo none > /sys/kernel/debug/sched/preempt
> > make -C coding/linux.git/ -j256 bzImage
> >
> > <snip>
> > watchdog: BUG: soft lockup - CPU#28 stuck for 22s! [kworker/28:1:1760]
> > CPU: 28 PID: 1760 Comm: kworker/28:1 Kdump: loaded Not tainted 6.10.0-rc5 #95
> > Workqueue: events drain_vmap_area_work
> > RIP: 0010:smp_call_function_many_cond+0x1d8/0xbb0
> > ...
> > <snip>
> 
> Great to hear you're able to reproduce the issue.
> 
> I keep debugging, and the original patch (https://lore.kernel.org/all/ZogS_04dP5LlRlXN@pc636/T/) shows purge_vmap_node() iteratively releases kasan vmalloc
> allocations and flushes tlb for each vmap_area. There are 2805
> flush_tlb_kernel_range() calls in ftrace log.
>   * One is called in __purge_vmap_area_lazy().
>   * Others are called in kasan_release_vmalloc(): Called by purge_vmap_node().
>     - [Rough calculation] Each flush_tlb_kernel_range() runs about 7.5ms.
>       -- 2804 * 7.5ms = 21.03 seconds (That's why a soft lock is trigger)
> 
> If we combine all tlb flush operations into one operation in the call path
> 'purge_vmap_node()->kasan_release_vmalloc()', the running time of
> drain_vmap_area_work() can be saved greately. The idea is from the
> flush_tlb_kernel_range() call in __purge_vmap_area_lazy().
> And, the soft lockup won't not be triggered. Please refer to the following patch.
> Here is the test result based on 6.10:
> 
> [6.10 wo/ the patch below]
>   1. ftrace latency profiling (record a trace if the latency > 20s): Commands
>      echo 20000000 > /sys/kernel/debug/tracing/tracing_thresh
>      echo drain_vmap_area_work > /sys/kernel/debug/tracing/set_graph_function
>      echo function_graph > /sys/kernel/debug/tracing/current_tracer
>      echo 1 > /sys/kernel/debug/tracing/tracing_on
> 
>   2. Run `make -j $(nproc)` to compile the kernel source
> 
>   3. Once the soft lockup is reproduced, check the ftace:
>      cat /sys/kernel/debug/tracing/trace
>         # tracer: function_graph
>         #
>         # CPU  DURATION                  FUNCTION CALLS
>         # |     |   |                     |   |   |   |
>           76) $ 50412985 us |    } /* __purge_vmap_area_lazy */
>           76) $ 50412997 us |  } /* drain_vmap_area_work */
>           76) $ 29165911 us |    } /* __purge_vmap_area_lazy */
>           76) $ 29165926 us |  } /* drain_vmap_area_work */
>           91) $ 53629423 us |    } /* __purge_vmap_area_lazy */
>           91) $ 53629434 us |  } /* drain_vmap_area_work */
>           91) $ 28121014 us |    } /* __purge_vmap_area_lazy */
>           91) $ 28121026 us |  } /* drain_vmap_area_work */
> 
> 
> [6.10 w/ the patch below]
>   1. Repeat step 1-2 in "[6.10 wo/ the patch below]"
> 
>   2. The soft lockup is not triggered and the ftrace log is empty.
>      cat /sys/kernel/debug/tracing/trace
>      # tracer: function_graph
>      #
>      # CPU  DURATION                  FUNCTION CALLS
>      # |     |   |                     |   |   |   |
> 
> 
>   3. Setting 'tracing_thresh' to 10/5 seconds does not get any ftrace log.
> 
>   4. Setting 'tracing_thresh' to 1 second gets ftrace log.
>       cat /sys/kernel/tracing/trace
>       # tracer: function_graph
>       #
>       # CPU  DURATION                  FUNCTION CALLS
>       # |     |   |                     |   |   |   |
>         51) $ 1019695 us  |    } /* __purge_vmap_area_lazy */
>         51) $ 1019703 us  |  } /* drain_vmap_area_work */
>        198) $ 1018707 us  |    } /* __purge_vmap_area_lazy */
>        198) $ 1018718 us  |  } /* drain_vmap_area_work */
> 
>   5. Run the following test_vmalloc command without any issues
>      modprobe test_vmalloc nr_threads=$(nproc) run_test_mask=0x1 nr_pages=4
> 
> Could you please test this patch in your VM environment? 
> 
> ---
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 70d6a8f6e25d..ddbf42a1a7b7 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -55,6 +55,9 @@ extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
>  int kasan_populate_early_shadow(const void *shadow_start,
>  				const void *shadow_end);
>  
> +#define KASAN_VMALLOC_PAGE_RANGE 0x1 /* Apply existing page range */
> +#define KASAN_VMALLOC_TLB_FLUSH  0x2 /* TLB flush */
> +
>  #ifndef kasan_mem_to_shadow
>  static inline void *kasan_mem_to_shadow(const void *addr)
>  {
> @@ -511,7 +514,8 @@ void kasan_populate_early_vm_area_shadow(void *start, unsigned long size);
>  int kasan_populate_vmalloc(unsigned long addr, unsigned long size);
>  void kasan_release_vmalloc(unsigned long start, unsigned long end,
>  			   unsigned long free_region_start,
> -			   unsigned long free_region_end);
> +			   unsigned long free_region_end,
> +			   unsigned long flags);
>  
>  #else /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>  
> @@ -526,7 +530,8 @@ static inline int kasan_populate_vmalloc(unsigned long start,
>  static inline void kasan_release_vmalloc(unsigned long start,
>  					 unsigned long end,
>  					 unsigned long free_region_start,
> -					 unsigned long free_region_end) { }
> +					 unsigned long free_region_end,
> +					 unsigned long flags) { }
>  
>  #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>  
> @@ -561,7 +566,8 @@ static inline int kasan_populate_vmalloc(unsigned long start,
>  static inline void kasan_release_vmalloc(unsigned long start,
>  					 unsigned long end,
>  					 unsigned long free_region_start,
> -					 unsigned long free_region_end) { }
> +					 unsigned long free_region_end,
> +					 unsigned long flags) { }
>  
>  static inline void *kasan_unpoison_vmalloc(const void *start,
>  					   unsigned long size,
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index d6210ca48dda..88d1c9dcb507 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -489,7 +489,8 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
>   */
>  void kasan_release_vmalloc(unsigned long start, unsigned long end,
>  			   unsigned long free_region_start,
> -			   unsigned long free_region_end)
> +			   unsigned long free_region_end,
> +			   unsigned long flags)
>  {
>  	void *shadow_start, *shadow_end;
>  	unsigned long region_start, region_end;
> @@ -522,12 +523,17 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
>  			__memset(shadow_start, KASAN_SHADOW_INIT, shadow_end - shadow_start);
>  			return;
>  		}
> -		apply_to_existing_page_range(&init_mm,
> +
> +
> +		if (flags & KASAN_VMALLOC_PAGE_RANGE)
> +			apply_to_existing_page_range(&init_mm,
>  					     (unsigned long)shadow_start,
>  					     size, kasan_depopulate_vmalloc_pte,
>  					     NULL);
> -		flush_tlb_kernel_range((unsigned long)shadow_start,
> -				       (unsigned long)shadow_end);
> +
> +		if (flags & KASAN_VMALLOC_TLB_FLUSH)
> +			flush_tlb_kernel_range((unsigned long)shadow_start,
> +					       (unsigned long)shadow_end);
>  	}
>  }
>  
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index e34ea860153f..d66e09135876 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2193,8 +2193,15 @@ static void purge_vmap_node(struct work_struct *work)
>  	struct vmap_area *va, *n_va;
>  	LIST_HEAD(local_list);
>  
> +	unsigned long start;
> +	unsigned long end;
> +
>  	vn->nr_purged = 0;
>  
> +	start = list_first_entry(&vn->purge_list, struct vmap_area, list)->va_start;
> +
> +	end = list_last_entry(&vn->purge_list, struct vmap_area, list)->va_end;
> +
>  	list_for_each_entry_safe(va, n_va, &vn->purge_list, list) {
>  		unsigned long nr = (va->va_end - va->va_start) >> PAGE_SHIFT;
>  		unsigned long orig_start = va->va_start;
> @@ -2205,7 +2212,8 @@ static void purge_vmap_node(struct work_struct *work)
>  
>  		if (is_vmalloc_or_module_addr((void *)orig_start))
>  			kasan_release_vmalloc(orig_start, orig_end,
> -					      va->va_start, va->va_end);
> +					      va->va_start, va->va_end,
> +					      KASAN_VMALLOC_PAGE_RANGE);
>  
>  		atomic_long_sub(nr, &vmap_lazy_nr);
>  		vn->nr_purged++;
> @@ -2218,6 +2226,8 @@ static void purge_vmap_node(struct work_struct *work)
>  		list_add(&va->list, &local_list);
>  	}
>  
> +	kasan_release_vmalloc(start, end, start, end, KASAN_VMALLOC_TLB_FLUSH);
> +
>  	reclaim_list_global(&local_list);
>  }
>  
> @@ -4726,7 +4736,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
>  				&free_vmap_area_list);
>  		if (va)
>  			kasan_release_vmalloc(orig_start, orig_end,
> -				va->va_start, va->va_end);
> +				va->va_start, va->va_end,
> +				KASAN_VMALLOC_PAGE_RANGE | KASAN_VMALLOC_TLB_FLUSH);
>  		vas[area] = NULL;
>  	}
>  
> @@ -4776,7 +4787,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
>  				&free_vmap_area_list);
>  		if (va)
>  			kasan_release_vmalloc(orig_start, orig_end,
> -				va->va_start, va->va_end);
> +				va->va_start, va->va_end,
> +				KASAN_VMALLOC_PAGE_RANGE | KASAN_VMALLOC_TLB_FLUSH);
>  		vas[area] = NULL;
>  		kfree(vms[area]);
>  	}
>
Sure! I will have a look at the patch and check my environment.

--
Uladzislau Rezki