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Wed, 07 May 2025 07:26:07 -0700 (PDT) Received: from localhost.localdomain ([121.185.186.233]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22e5369bea0sm26031595ad.117.2025.05.07.07.26.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 May 2025 07:26:06 -0700 (PDT) From: Jeongjun Park To: akpm@linux-foundation.org, urezki@gmail.com Cc: edumazet@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jeongjun Park Subject: [PATCH v3] mm/vmalloc: fix data race in show_numa_info() Date: Wed, 7 May 2025 23:25:52 +0900 Message-ID: <20250507142552.9446-1-aha310510@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The following data-race was found in show_numa_info(): =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 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 new_sync_read fs/read_write.c:489 [inline] vfs_read+0x5b4/0x740 fs/read_write.c:570 ksys_read+0xbe/0x190 fs/read_write.c:713 __do_sys_read fs/read_write.c:722 [inline] __se_sys_read fs/read_write.c:720 [inline] __x64_sys_read+0x41/0x50 fs/read_write.c:720 x64_sys_call+0x1729/0x1fd0 arch/x86/include/generated/asm/syscalls_64.h:1 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xa6/0x1b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f 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 new_sync_read fs/read_write.c:489 [inline] vfs_read+0x5b4/0x740 fs/read_write.c:570 ksys_read+0xbe/0x190 fs/read_write.c:713 __do_sys_read fs/read_write.c:722 [inline] __se_sys_read fs/read_write.c:720 [inline] __x64_sys_read+0x41/0x50 fs/read_write.c:720 x64_sys_call+0x1729/0x1fd0 arch/x86/include/generated/asm/syscalls_64.h:1 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xa6/0x1b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f value changed: 0x0000008f -> 0x00000000 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 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, show_numa_info() should allocate the heap. One thing to note is that show_numa_info() is called in a critical section of a spinlock, so it must be allocated on the heap with GFP_ATOMIC flag. Fixes: a47a126ad5ea ("vmallocinfo: add NUMA information") Suggested-by: Eric Dumazet Suggested-by: Uladzislau Rezki (Sony) Signed-off-by: Jeongjun Park --- 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 | 51 ++++++++++++++++++++++++++------------------------- 1 file changed, 26 insertions(+), 25 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 3ed720a787ec..9139025e20e5 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -4914,28 +4914,32 @@ bool vmalloc_dump_obj(void *object) #endif =20 #ifdef CONFIG_PROC_FS + +/* + * 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) { - if (IS_ENABLED(CONFIG_NUMA)) { - unsigned int nr, *counters =3D m->private; - unsigned int step =3D 1U << vm_area_page_order(v); + unsigned int nr, *counters; + unsigned int step =3D 1U << vm_area_page_order(v); =20 - if (!counters) - return; + counters =3D kcalloc(nr_node_ids, sizeof(unsigned int), GFP_ATOMIC); + if (!counters) + return; =20 - if (v->flags & VM_UNINITIALIZED) - return; - /* Pair with smp_wmb() in clear_vm_uninitialized_flag() */ - smp_rmb(); + /* Pair with smp_wmb() in clear_vm_uninitialized_flag() */ + smp_rmb(); =20 - memset(counters, 0, nr_node_ids * sizeof(unsigned int)); + for (nr =3D 0; nr < v->nr_pages; nr +=3D step) + counters[page_to_nid(v->pages[nr])] +=3D step; + for_each_node_state(nr, N_HIGH_MEMORY) + if (counters[nr]) + seq_printf(m, " N%u=3D%u", nr, counters[nr]); =20 - for (nr =3D 0; nr < v->nr_pages; nr +=3D step) - counters[page_to_nid(v->pages[nr])] +=3D step; - for_each_node_state(nr, N_HIGH_MEMORY) - if (counters[nr]) - seq_printf(m, " N%u=3D%u", nr, counters[nr]); - } + kfree(counters); } =20 static void show_purge_info(struct seq_file *m) @@ -4979,6 +4983,8 @@ static int vmalloc_info_show(struct seq_file *m, void= *p) } =20 v =3D va->vm; + if (v->flags & VM_UNINITIALIZED) + continue; =20 seq_printf(m, "0x%pK-0x%pK %7ld", v->addr, v->addr + v->size, v->size); @@ -5013,7 +5019,9 @@ static int vmalloc_info_show(struct seq_file *m, void= *p) if (is_vmalloc_addr(v->pages)) seq_puts(m, " vpages"); =20 - show_numa_info(m, v); + if (IS_ENABLED(CONFIG_NUMA)) + show_numa_info(m, v); + seq_putc(m, '\n'); } spin_unlock(&vn->busy.lock); @@ -5028,14 +5036,7 @@ static int vmalloc_info_show(struct seq_file *m, voi= d *p) =20 static int __init proc_vmalloc_init(void) { - void *priv_data =3D NULL; - - if (IS_ENABLED(CONFIG_NUMA)) - priv_data =3D kmalloc(nr_node_ids * sizeof(unsigned int), GFP_KERNEL); - - proc_create_single_data("vmallocinfo", - 0400, NULL, vmalloc_info_show, priv_data); - + proc_create_single("vmallocinfo", 0400, NULL, vmalloc_info_show); return 0; } module_init(proc_vmalloc_init); --