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
