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[95.203.26.253]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-32128ddfc71sm23334391fa.20.2025.05.08.05.51.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 May 2025 05:51:57 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 8 May 2025 14:51:55 +0200 To: Jeongjun Park Cc: akpm@linux-foundation.org, urezki@gmail.com, edumazet@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] mm/vmalloc: fix data race in show_numa_info() Message-ID: References: <20250508065558.149091-1-aha310510@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250508065558.149091-1-aha310510@gmail.com> On Thu, May 08, 2025 at 03:55:58PM +0900, Jeongjun Park wrote: > The following data-race was found in show_numa_info(): > > ================================================================== > BUG: KCSAN: data-race in vmalloc_info_show / vmalloc_info_show > > read to 0xffff88800971fe30 of 4 bytes by task 8289 on cpu 0: > show_numa_info mm/vmalloc.c:4936 [inline] > vmalloc_info_show+0x5a8/0x7e0 mm/vmalloc.c:5016 > seq_read_iter+0x373/0xb40 fs/seq_file.c:230 > proc_reg_read_iter+0x11e/0x170 fs/proc/inode.c:299 > .... > > write to 0xffff88800971fe30 of 4 bytes by task 8287 on cpu 1: > show_numa_info mm/vmalloc.c:4934 [inline] > vmalloc_info_show+0x38f/0x7e0 mm/vmalloc.c:5016 > seq_read_iter+0x373/0xb40 fs/seq_file.c:230 > proc_reg_read_iter+0x11e/0x170 fs/proc/inode.c:299 > .... > > value changed: 0x0000008f -> 0x00000000 > ================================================================== > > According to this report,there is a read/write data-race because m->private > is accessible to multiple CPUs. To fix this, instead of allocating the heap > in proc_vmalloc_init() and passing the heap address to m->private, > vmalloc_info_show() should allocate the heap. > > Fixes: a47a126ad5ea ("vmallocinfo: add NUMA information") > Suggested-by: Eric Dumazet > Suggested-by: Uladzislau Rezki (Sony) > Suggested-by: Andrew Morton > Signed-off-by: Jeongjun Park > --- > v4: Change the way counters array heap is allocated, per Andrew Morton's suggestion. > And fix it to call smp_rmb() in the correct location. > - Link to v3: https://lore.kernel.org/all/20250507142552.9446-1-aha310510@gmail.com/ > v3: Following Uladzislau Rezki's suggestion, we check v->flags beforehand > to avoid printing uninitialized members of vm_struct. > - Link to v2: https://lore.kernel.org/all/20250506082520.84153-1-aha310510@gmail.com/ > v2: Refactoring some functions and fix patch as per Eric Dumazet suggestion > - Link to v1: https://lore.kernel.org/all/20250505171948.24410-1-aha310510@gmail.com/ > --- > mm/vmalloc.c | 61 ++++++++++++++++++++++++++++------------------------ > 1 file changed, 33 insertions(+), 28 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 3ed720a787ec..112df5a86106 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -3100,7 +3100,7 @@ static void clear_vm_uninitialized_flag(struct vm_struct *vm) > /* > * Before removing VM_UNINITIALIZED, > * we should make sure that vm has proper values. > - * Pair with smp_rmb() in show_numa_info(). > + * Pair with smp_rmb() in vread_iter() and vmalloc_info_show(). > */ > smp_wmb(); > vm->flags &= ~VM_UNINITIALIZED; > @@ -4914,28 +4914,29 @@ bool vmalloc_dump_obj(void *object) > #endif > > #ifdef CONFIG_PROC_FS > -static void show_numa_info(struct seq_file *m, struct vm_struct *v) > -{ > - if (IS_ENABLED(CONFIG_NUMA)) { > - unsigned int nr, *counters = m->private; > - unsigned int step = 1U << vm_area_page_order(v); > > - if (!counters) > - return; > +/* > + * Print number of pages allocated on each memory node. > + * > + * This function can only be called if CONFIG_NUMA is enabled > + * and VM_UNINITIALIZED bit in v->flags is disabled. > + */ > +static void show_numa_info(struct seq_file *m, struct vm_struct *v, > + unsigned int *counters) > +{ > + unsigned int nr; > + unsigned int step = 1U << vm_area_page_order(v); > > - if (v->flags & VM_UNINITIALIZED) > - return; > - /* Pair with smp_wmb() in clear_vm_uninitialized_flag() */ > - smp_rmb(); > + if (!counters) > + return; > > - memset(counters, 0, nr_node_ids * sizeof(unsigned int)); > + memset(counters, 0, nr_node_ids * sizeof(unsigned int)); > > - for (nr = 0; nr < v->nr_pages; nr += step) > - counters[page_to_nid(v->pages[nr])] += step; > - for_each_node_state(nr, N_HIGH_MEMORY) > - if (counters[nr]) > - seq_printf(m, " N%u=%u", nr, counters[nr]); > - } > + for (nr = 0; nr < v->nr_pages; nr += step) > + counters[page_to_nid(v->pages[nr])] += step; > + for_each_node_state(nr, N_HIGH_MEMORY) > + if (counters[nr]) > + seq_printf(m, " N%u=%u", nr, counters[nr]); > } > > static void show_purge_info(struct seq_file *m) > @@ -4962,8 +4963,11 @@ static int vmalloc_info_show(struct seq_file *m, void *p) > struct vmap_node *vn; > struct vmap_area *va; > struct vm_struct *v; > + unsigned int *counters = NULL; > Setting NULL can be dropped. > int i; > > + counters = kmalloc(nr_node_ids * sizeof(unsigned int), GFP_KERNEL); "if (IS_ENABLED(CONFIG_NUMA))"? If no NUMA, allocating and freeing sounds like without any reason. > + > for (i = 0; i < nr_vmap_nodes; i++) { > vn = &vmap_nodes[i]; > > @@ -4979,6 +4983,11 @@ static int vmalloc_info_show(struct seq_file *m, void *p) > } > > v = va->vm; > + if (v->flags & VM_UNINITIALIZED) > + continue; > + > + /* Pair with smp_wmb() in clear_vm_uninitialized_flag() */ > + smp_rmb(); > > seq_printf(m, "0x%pK-0x%pK %7ld", > v->addr, v->addr + v->size, v->size); > @@ -5013,7 +5022,9 @@ static int vmalloc_info_show(struct seq_file *m, void *p) > if (is_vmalloc_addr(v->pages)) > seq_puts(m, " vpages"); > > - show_numa_info(m, v); > + if (IS_ENABLED(CONFIG_NUMA)) > + show_numa_info(m, v, counters); > + > seq_putc(m, '\n'); > } > spin_unlock(&vn->busy.lock); > @@ -5023,19 +5034,13 @@ static int vmalloc_info_show(struct seq_file *m, void *p) > * As a final step, dump "unpurged" areas. > */ > show_purge_info(m); > + kfree(counters); > Maybe check for NULL before and IS_ENABLED(CONFIG_NUMA)? -- Uladzislau Rezki