* [PATCH] mm/vmalloc: fix data race in show_numa_info()
@ 2025-05-05 17:19 Jeongjun Park
2025-05-05 18:06 ` Eric Dumazet
0 siblings, 1 reply; 4+ messages in thread
From: Jeongjun Park @ 2025-05-05 17:19 UTC (permalink / raw)
To: akpm; +Cc: urezki, edumazet, linux-mm, linux-kernel, Jeongjun Park
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
Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 8287 Comm: syz.0.411 Not tainted 6.15.0-rc4-00256-g95d3481af6dc-dirty #1 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
==================================================================
There is a read/write data-race in counter[]. This seems to be happening
because only read memory barriers are currently applied, so we need to
modify the write operation to counters[] to be handled atomically.
Fixes: a47a126ad5ea ("vmallocinfo: add NUMA information")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
mm/vmalloc.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 3ed720a787ec..d93fa535bc21 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4917,7 +4917,8 @@ bool vmalloc_dump_obj(void *object)
static void show_numa_info(struct seq_file *m, struct vm_struct *v)
{
if (IS_ENABLED(CONFIG_NUMA)) {
- unsigned int nr, *counters = m->private;
+ atomic_t *counters = m->private;
+ unsigned int nr;
unsigned int step = 1U << vm_area_page_order(v);
if (!counters)
@@ -4931,10 +4932,10 @@ static void show_numa_info(struct seq_file *m, struct vm_struct *v)
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;
+ atomic_add(step, &counters[page_to_nid(v->pages[nr])]);
for_each_node_state(nr, N_HIGH_MEMORY)
- if (counters[nr])
- seq_printf(m, " N%u=%u", nr, counters[nr]);
+ if (atomic_read(&counters[nr]))
+ seq_printf(m, " N%u=%u", nr, atomic_read(&counters[nr]));
}
}
--
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm/vmalloc: fix data race in show_numa_info()
2025-05-05 17:19 [PATCH] mm/vmalloc: fix data race in show_numa_info() Jeongjun Park
@ 2025-05-05 18:06 ` Eric Dumazet
2025-05-05 20:09 ` Eric Dumazet
0 siblings, 1 reply; 4+ messages in thread
From: Eric Dumazet @ 2025-05-05 18:06 UTC (permalink / raw)
To: Jeongjun Park; +Cc: akpm, urezki, linux-mm, linux-kernel
On Mon, May 5, 2025 at 10:20 AM Jeongjun Park <aha310510@gmail.com> wrote:
>
> The following data-race was found in show_numa_info():
>
> ==================================================================
> BUG: KCSAN: data-race in vmalloc_info_show / vmalloc_info_show
>
> r
> value changed: 0x0000008f -> 0x00000000
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 UID: 0 PID: 8287 Comm: syz.0.411 Not tainted 6.15.0-rc4-00256-g95d3481af6dc-dirty #1 PREEMPT(voluntary)
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> ==================================================================
>
> There is a read/write data-race in counter[]. This seems to be happening
> because only read memory barriers are currently applied, so we need to
> modify the write operation to counters[] to be handled atomically.
>
> Fixes: a47a126ad5ea ("vmallocinfo: add NUMA information")
> Signed-off-by: Jeongjun Park <aha310510@gmail.com>
> ---
> mm/vmalloc.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 3ed720a787ec..d93fa535bc21 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -4917,7 +4917,8 @@ bool vmalloc_dump_obj(void *object)
> static void show_numa_info(struct seq_file *m, struct vm_struct *v)
> {
> if (IS_ENABLED(CONFIG_NUMA)) {
> - unsigned int nr, *counters = m->private;
> + atomic_t *counters = m->private;
> + unsigned int nr;
> unsigned int step = 1U << vm_area_page_order(v);
>
> if (!counters)
> @@ -4931,10 +4932,10 @@ static void show_numa_info(struct seq_file *m, struct vm_struct *v)
> 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;
> + atomic_add(step, &counters[page_to_nid(v->pages[nr])]);
> for_each_node_state(nr, N_HIGH_MEMORY)
> - if (counters[nr])
> - seq_printf(m, " N%u=%u", nr, counters[nr]);
> + if (atomic_read(&counters[nr]))
> + seq_printf(m, " N%u=%u", nr, atomic_read(&counters[nr]));
> }
> }
>
> --
This patch looks bogus to me.
The race is about using m->private for storage, while the same file
can be read from multiple threads.
Using atomic_t is going to silence syzbot, but the bug is still there.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm/vmalloc: fix data race in show_numa_info()
2025-05-05 18:06 ` Eric Dumazet
@ 2025-05-05 20:09 ` Eric Dumazet
2025-05-06 5:44 ` Jeongjun Park
0 siblings, 1 reply; 4+ messages in thread
From: Eric Dumazet @ 2025-05-05 20:09 UTC (permalink / raw)
To: Jeongjun Park; +Cc: akpm, urezki, linux-mm, linux-kernel
On Mon, May 5, 2025 at 11:06 AM Eric Dumazet <edumazet@google.com> wrote:
>
> On Mon, May 5, 2025 at 10:20 AM Jeongjun Park <aha310510@gmail.com> wrote:
> >
> > The following data-race was found in show_numa_info():
> >
> > ==================================================================
> > BUG: KCSAN: data-race in vmalloc_info_show / vmalloc_info_show
> >
> > r
> > value changed: 0x0000008f -> 0x00000000
> >
> > Reported by Kernel Concurrency Sanitizer on:
> > CPU: 1 UID: 0 PID: 8287 Comm: syz.0.411 Not tainted 6.15.0-rc4-00256-g95d3481af6dc-dirty #1 PREEMPT(voluntary)
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> > ==================================================================
> >
> > There is a read/write data-race in counter[]. This seems to be happening
> > because only read memory barriers are currently applied, so we need to
> > modify the write operation to counters[] to be handled atomically.
> >
> > Fixes: a47a126ad5ea ("vmallocinfo: add NUMA information")
> > Signed-off-by: Jeongjun Park <aha310510@gmail.com>
> > ---
> > mm/vmalloc.c | 9 +++++----
> > 1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 3ed720a787ec..d93fa535bc21 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -4917,7 +4917,8 @@ bool vmalloc_dump_obj(void *object)
> > static void show_numa_info(struct seq_file *m, struct vm_struct *v)
> > {
> > if (IS_ENABLED(CONFIG_NUMA)) {
> > - unsigned int nr, *counters = m->private;
> > + atomic_t *counters = m->private;
> > + unsigned int nr;
> > unsigned int step = 1U << vm_area_page_order(v);
> >
> > if (!counters)
> > @@ -4931,10 +4932,10 @@ static void show_numa_info(struct seq_file *m, struct vm_struct *v)
> > 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;
> > + atomic_add(step, &counters[page_to_nid(v->pages[nr])]);
> > for_each_node_state(nr, N_HIGH_MEMORY)
> > - if (counters[nr])
> > - seq_printf(m, " N%u=%u", nr, counters[nr]);
> > + if (atomic_read(&counters[nr]))
> > + seq_printf(m, " N%u=%u", nr, atomic_read(&counters[nr]));
> > }
> > }
> >
> > --
>
> This patch looks bogus to me.
>
> The race is about using m->private for storage, while the same file
> can be read from multiple threads.
>
> Using atomic_t is going to silence syzbot, but the bug is still there.
A more correct fix would be :
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a6e7acebe9adf5e6c8abd52dcf7d02a6a1bc3030..cb69b44587d2032a6192f3ceb518490a05eff541
100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4921,24 +4921,24 @@ bool vmalloc_dump_obj(void *object)
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 nr, *counters;
unsigned int step = 1U << vm_area_page_order(v);
+ if (v->flags & VM_UNINITIALIZED)
+ return;
+ counters = kcalloc(nr_node_ids, sizeof(unsigned int),
GFP_KERNEL);
if (!counters)
return;
- if (v->flags & VM_UNINITIALIZED)
- return;
/* 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]);
+ kfree(counters);
}
}
@@ -5032,13 +5032,7 @@ 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);
return 0;
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm/vmalloc: fix data race in show_numa_info()
2025-05-05 20:09 ` Eric Dumazet
@ 2025-05-06 5:44 ` Jeongjun Park
0 siblings, 0 replies; 4+ messages in thread
From: Jeongjun Park @ 2025-05-06 5:44 UTC (permalink / raw)
To: Eric Dumazet; +Cc: akpm, urezki, linux-mm, linux-kernel
Eric Dumazet <edumazet@google.com> wrote:
>
> On Mon, May 5, 2025 at 11:06 AM Eric Dumazet <edumazet@google.com> wrote:
> >
> > On Mon, May 5, 2025 at 10:20 AM Jeongjun Park <aha310510@gmail.com> wrote:
> > >
> > > The following data-race was found in show_numa_info():
> > >
> > > ==================================================================
> > > BUG: KCSAN: data-race in vmalloc_info_show / vmalloc_info_show
> > >
> > > r
> > > value changed: 0x0000008f -> 0x00000000
> > >
> > > Reported by Kernel Concurrency Sanitizer on:
> > > CPU: 1 UID: 0 PID: 8287 Comm: syz.0.411 Not tainted 6.15.0-rc4-00256-g95d3481af6dc-dirty #1 PREEMPT(voluntary)
> > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> > > ==================================================================
> > >
> > > There is a read/write data-race in counter[]. This seems to be happening
> > > because only read memory barriers are currently applied, so we need to
> > > modify the write operation to counters[] to be handled atomically.
> > >
> > > Fixes: a47a126ad5ea ("vmallocinfo: add NUMA information")
> > > Signed-off-by: Jeongjun Park <aha310510@gmail.com>
> > > ---
> > > mm/vmalloc.c | 9 +++++----
> > > 1 file changed, 5 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > index 3ed720a787ec..d93fa535bc21 100644
> > > --- a/mm/vmalloc.c
> > > +++ b/mm/vmalloc.c
> > > @@ -4917,7 +4917,8 @@ bool vmalloc_dump_obj(void *object)
> > > static void show_numa_info(struct seq_file *m, struct vm_struct *v)
> > > {
> > > if (IS_ENABLED(CONFIG_NUMA)) {
> > > - unsigned int nr, *counters = m->private;
> > > + atomic_t *counters = m->private;
> > > + unsigned int nr;
> > > unsigned int step = 1U << vm_area_page_order(v);
> > >
> > > if (!counters)
> > > @@ -4931,10 +4932,10 @@ static void show_numa_info(struct seq_file *m, struct vm_struct *v)
> > > 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;
> > > + atomic_add(step, &counters[page_to_nid(v->pages[nr])]);
> > > for_each_node_state(nr, N_HIGH_MEMORY)
> > > - if (counters[nr])
> > > - seq_printf(m, " N%u=%u", nr, counters[nr]);
> > > + if (atomic_read(&counters[nr]))
> > > + seq_printf(m, " N%u=%u", nr, atomic_read(&counters[nr]));
> > > }
> > > }
> > >
> > > --
> >
> > This patch looks bogus to me.
> >
> > The race is about using m->private for storage, while the same file
> > can be read from multiple threads.
> >
> > Using atomic_t is going to silence syzbot, but the bug is still there.
>
> A more correct fix would be :
>
Thanks for your suggestion! It definitely looks much better this way.
I'll do some refactoring on show_numa_info() and send out a
v2 patch.
Regards,
Jeongjun Park
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a6e7acebe9adf5e6c8abd52dcf7d02a6a1bc3030..cb69b44587d2032a6192f3ceb518490a05eff541
> 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -4921,24 +4921,24 @@ bool vmalloc_dump_obj(void *object)
> 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 nr, *counters;
> unsigned int step = 1U << vm_area_page_order(v);
>
> + if (v->flags & VM_UNINITIALIZED)
> + return;
> + counters = kcalloc(nr_node_ids, sizeof(unsigned int),
> GFP_KERNEL);
> if (!counters)
> return;
>
> - if (v->flags & VM_UNINITIALIZED)
> - return;
> /* 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]);
> + kfree(counters);
> }
> }
>
> @@ -5032,13 +5032,7 @@ 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);
>
> return 0;
> }
^ permalink raw reply [flat|nested] 4+ messages in thread
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2025-05-05 17:19 [PATCH] mm/vmalloc: fix data race in show_numa_info() Jeongjun Park
2025-05-05 18:06 ` Eric Dumazet
2025-05-05 20:09 ` Eric Dumazet
2025-05-06 5:44 ` Jeongjun Park
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