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Thu, 08 May 2025 06:35:46 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250508065558.149091-1-aha310510@gmail.com> In-Reply-To: From: Jeongjun Park Date: Thu, 8 May 2025 22:35:37 +0900 X-Gm-Features: ATxdqUGmB4SFgx7KWzfPXB2ytFLx8C_yqKkywCIeBIwxDqEjIseu0ZDsugTUaOI Message-ID: Subject: Re: [PATCH v4] mm/vmalloc: fix data race in show_numa_info() To: Uladzislau Rezki Cc: akpm@linux-foundation.org, edumazet@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Uladzislau Rezki wrote: > > 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 Hmm....then I think patching vmalloc_info_show() like this should work. --- mm/vmalloc.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 3ed720a787ec..b60355256211 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -4962,8 +4962,12 @@ 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; int i; + if (IS_ENABLED(CONFIG_NUMA)) + counters = kmalloc(nr_node_ids * sizeof(unsigned int), GFP_KERNEL); + for (i = 0; i < nr_vmap_nodes; i++) { vn = &vmap_nodes[i]; @@ -5013,7 +5017,9 @@ 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 (counters) + show_numa_info(m, v, counters); + seq_putc(m, '\n'); } spin_unlock(&vn->busy.lock); @@ -5023,6 +5029,7 @@ static int vmalloc_info_show(struct seq_file *m, void *p) * As a final step, dump "unpurged" areas. */ show_purge_info(m); + kfree(counters); return 0; } -- This way, we won't allocate heap unnecessarily when CONFIG_NUMA is disabled, and we only need to check if counters are NULL or not before calling show_numa_info(). However, if you change it like this, counters must always be initialized to NULL. Regards, Jeongjun Park