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Message-ID: <CAO9qdTHB+kaPX7u3hDQUz1q805nmhtfRUWguZEWX=hcfcU1Uow@mail.gmail.com>
Date: Thu, 8 May 2025 15:18:39 +0900
From: Jeongjun Park <aha310510@...il.com>
To: Ozgur Kara <ozgur@...sey.org>
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> wrote:
>
> Ozgur Kara <ozgur@...sey.org> wrote:
> >
> > 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;
> > }
> >
>
> Thanks for the suggestion! Not related to data-race, but it seems like
> a good idea to add some check code in case null-deref occurs. I'll reflect
> this in the v4 patch.
>
> Regards,
>
> Jeongjun Park
>
Oh, I misread the code. This function already checks if the va->vm
value is null, so there's no need to do this duplicate check.
Regards,
Jeongjun Park
> > > - 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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