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Message-ID: <01100196acf1ed92-b7371c69-31bd-42d4-b691-55216da8cc93-000000@eu-north-1.amazonses.com>
Date: Wed, 7 May 2025 22:50:58 +0000
From: Ozgur Kara <ozgur@...sey.org>
To: Jeongjun Park <aha310510@...il.com>
Cc: akpm@...ux-foundation.org, urezki@...il.com, edumazet@...gle.com,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm/vmalloc: fix data race in show_numa_info()
Jeongjun Park <aha310510@...il.com>, 7 May 2025 Çar, 17:32 tarihinde şunu yazdı:
>
> 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
> 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
> ==================================================================
>
> 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 <edumazet@...gle.com>
> Suggested-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> Signed-off-by: Jeongjun Park <aha310510@...il.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 | 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
>
> #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 = m->private;
> - unsigned int step = 1U << vm_area_page_order(v);
> + unsigned int nr, *counters;
> + unsigned int step = 1U << vm_area_page_order(v);
>
> - if (!counters)
> - return;
> + counters = kcalloc(nr_node_ids, sizeof(unsigned int), GFP_ATOMIC);
> + if (!counters)
> + return;
>
> - if (v->flags & VM_UNINITIALIZED)
Hello,
although skipping memory blocks with VM_UNINITIALIZED flag seems like
a good idea maybe it might be a good idea to check correctness of
memory areas.
if (v && (v->flags & VM_UNINITIALIZED)) {
continue;
}
> - return;
> - /* Pair with smp_wmb() in clear_vm_uninitialized_flag() */
> - smp_rmb();
> + /* Pair with smp_wmb() in clear_vm_uninitialized_flag() */
> + smp_rmb();
>
> - 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]);
> - }
> + kfree(counters);
> }
>
> static void show_purge_info(struct seq_file *m)
> @@ -4979,6 +4983,8 @@ static int vmalloc_info_show(struct seq_file *m, void *p)
> }
>
> v = va->vm;
> + if (v->flags & VM_UNINITIALIZED)
> + continue;
>
> 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");
>
> - 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, void *p)
>
> static int __init proc_vmalloc_init(void)
> {
> - void *priv_data = NULL;
> -
> - if (IS_ENABLED(CONFIG_NUMA))
> - priv_data = 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);
proc_create_single function clean but it no longer receives data like
priv_data right? so if priv_data is needed again code will not work.
if use priv_data becomes necessary, a suitable memory allocation and
release mechanism should be added for this.
otherwise a memory leak could occur and perhaps the use of kfree
instead of kmalloc could also be added.
proc_create_single_data("vmallocinfo", 0400, NULL, vmalloc_info_show,
priv_data);
// use kfree and free priv_data
kfree(priv_data);
Regards
Ozgur
> return 0;
> }
> module_init(proc_vmalloc_init);
> --
>
>
>
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