KCSAN found an issue in obj_stock_flush_required():
stock->cached_objcg can be reset between the check and dereference:
==================================================================
BUG: KCSAN: data-race in drain_all_stock / drain_obj_stock
write to 0xffff888237c2a2f8 of 8 bytes by task 19625 on cpu 0:
drain_obj_stock+0x408/0x4e0 mm/memcontrol.c:3306
refill_obj_stock+0x9c/0x1e0 mm/memcontrol.c:3340
obj_cgroup_uncharge+0xe/0x10 mm/memcontrol.c:3408
memcg_slab_free_hook mm/slab.h:587 [inline]
__cache_free mm/slab.c:3373 [inline]
__do_kmem_cache_free mm/slab.c:3577 [inline]
kmem_cache_free+0x105/0x280 mm/slab.c:3602
__d_free fs/dcache.c:298 [inline]
dentry_free fs/dcache.c:375 [inline]
__dentry_kill+0x422/0x4a0 fs/dcache.c:621
dentry_kill+0x8d/0x1e0
dput+0x118/0x1f0 fs/dcache.c:913
__fput+0x3bf/0x570 fs/file_table.c:329
____fput+0x15/0x20 fs/file_table.c:349
task_work_run+0x123/0x160 kernel/task_work.c:179
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
exit_to_user_mode_loop+0xcf/0xe0 kernel/entry/common.c:171
exit_to_user_mode_prepare+0x6a/0xa0 kernel/entry/common.c:203
__syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
syscall_exit_to_user_mode+0x26/0x140 kernel/entry/common.c:296
do_syscall_64+0x4d/0xc0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd
read to 0xffff888237c2a2f8 of 8 bytes by task 19632 on cpu 1:
obj_stock_flush_required mm/memcontrol.c:3319 [inline]
drain_all_stock+0x174/0x2a0 mm/memcontrol.c:2361
try_charge_memcg+0x6d0/0xd10 mm/memcontrol.c:2703
try_charge mm/memcontrol.c:2837 [inline]
mem_cgroup_charge_skmem+0x51/0x140 mm/memcontrol.c:7290
sock_reserve_memory+0xb1/0x390 net/core/sock.c:1025
sk_setsockopt+0x800/0x1e70 net/core/sock.c:1525
udp_lib_setsockopt+0x99/0x6c0 net/ipv4/udp.c:2692
udp_setsockopt+0x73/0xa0 net/ipv4/udp.c:2817
sock_common_setsockopt+0x61/0x70 net/core/sock.c:3668
__sys_setsockopt+0x1c3/0x230 net/socket.c:2271
__do_sys_setsockopt net/socket.c:2282 [inline]
__se_sys_setsockopt net/socket.c:2279 [inline]
__x64_sys_setsockopt+0x66/0x80 net/socket.c:2279
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
value changed: 0xffff8881382d52c0 -> 0xffff888138893740
Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19632 Comm: syz-executor.0 Not tainted 6.3.0-rc2-syzkaller-00387-g534293368afa #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
Fix it by using READ_ONCE()/WRITE_ONCE() for all accesses to
stock->cached_objcg.
Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
Reported-by: [email protected]
Reported-by: Dmitry Vyukov <[email protected]>
Link:
https://lore.kernel.org/linux-mm/CACT4Y+ZfucZhM60YPphWiCLJr6+SGFhT+jjm8k1P-a_8Kkxsjg@mail.gmail.com/T/#t
Signed-off-by: Roman Gushchin <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Cc: Shakeel Butt <[email protected]>
---
mm/memcontrol.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4b27e245a055..c823c35c2ed4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3208,12 +3208,12 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
* accumulating over a page of vmstat data or when pgdat or idx
* changes.
*/
- if (stock->cached_objcg != objcg) {
+ if (READ_ONCE(stock->cached_objcg) != objcg) {
old = drain_obj_stock(stock);
obj_cgroup_get(objcg);
stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
- stock->cached_objcg = objcg;
+ WRITE_ONCE(stock->cached_objcg, objcg);
stock->cached_pgdat = pgdat;
} else if (stock->cached_pgdat != pgdat) {
/* Flush the existing cached vmstat data */
@@ -3267,7 +3267,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
local_lock_irqsave(&memcg_stock.stock_lock, flags);
stock = this_cpu_ptr(&memcg_stock);
- if (objcg == stock->cached_objcg && stock->nr_bytes >= nr_bytes) {
+ if (objcg == READ_ONCE(stock->cached_objcg) && stock->nr_bytes >= nr_bytes) {
stock->nr_bytes -= nr_bytes;
ret = true;
}
@@ -3279,7 +3279,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock)
{
- struct obj_cgroup *old = stock->cached_objcg;
+ struct obj_cgroup *old = READ_ONCE(stock->cached_objcg);
if (!old)
return NULL;
@@ -3332,7 +3332,7 @@ static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock)
stock->cached_pgdat = NULL;
}
- stock->cached_objcg = NULL;
+ WRITE_ONCE(stock->cached_objcg, NULL);
/*
* The `old' objects needs to be released by the caller via
* obj_cgroup_put() outside of memcg_stock_pcp::stock_lock.
@@ -3343,10 +3343,11 @@ static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock)
static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
struct mem_cgroup *root_memcg)
{
+ struct obj_cgroup *objcg = READ_ONCE(stock->cached_objcg);
struct mem_cgroup *memcg;
- if (stock->cached_objcg) {
- memcg = obj_cgroup_memcg(stock->cached_objcg);
+ if (objcg) {
+ memcg = obj_cgroup_memcg(objcg);
if (memcg && mem_cgroup_is_descendant(memcg, root_memcg))
return true;
}
@@ -3365,10 +3366,10 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
local_lock_irqsave(&memcg_stock.stock_lock, flags);
stock = this_cpu_ptr(&memcg_stock);
- if (stock->cached_objcg != objcg) { /* reset if necessary */
+ if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */
old = drain_obj_stock(stock);
obj_cgroup_get(objcg);
- stock->cached_objcg = objcg;
+ WRITE_ONCE(stock->cached_objcg, objcg);
stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
allow_uncharge = true; /* Allow uncharge when objcg changes */
--
2.40.1
On Tue, May 2, 2023 at 9:09 AM Roman Gushchin <[email protected]> wrote:
>
> KCSAN found an issue in obj_stock_flush_required():
> stock->cached_objcg can be reset between the check and dereference:
>
> ==================================================================
> BUG: KCSAN: data-race in drain_all_stock / drain_obj_stock
>
> write to 0xffff888237c2a2f8 of 8 bytes by task 19625 on cpu 0:
> drain_obj_stock+0x408/0x4e0 mm/memcontrol.c:3306
> refill_obj_stock+0x9c/0x1e0 mm/memcontrol.c:3340
> obj_cgroup_uncharge+0xe/0x10 mm/memcontrol.c:3408
> memcg_slab_free_hook mm/slab.h:587 [inline]
> __cache_free mm/slab.c:3373 [inline]
> __do_kmem_cache_free mm/slab.c:3577 [inline]
> kmem_cache_free+0x105/0x280 mm/slab.c:3602
> __d_free fs/dcache.c:298 [inline]
> dentry_free fs/dcache.c:375 [inline]
> __dentry_kill+0x422/0x4a0 fs/dcache.c:621
> dentry_kill+0x8d/0x1e0
> dput+0x118/0x1f0 fs/dcache.c:913
> __fput+0x3bf/0x570 fs/file_table.c:329
> ____fput+0x15/0x20 fs/file_table.c:349
> task_work_run+0x123/0x160 kernel/task_work.c:179
> resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
> exit_to_user_mode_loop+0xcf/0xe0 kernel/entry/common.c:171
> exit_to_user_mode_prepare+0x6a/0xa0 kernel/entry/common.c:203
> __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
> syscall_exit_to_user_mode+0x26/0x140 kernel/entry/common.c:296
> do_syscall_64+0x4d/0xc0 arch/x86/entry/common.c:86
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> read to 0xffff888237c2a2f8 of 8 bytes by task 19632 on cpu 1:
> obj_stock_flush_required mm/memcontrol.c:3319 [inline]
> drain_all_stock+0x174/0x2a0 mm/memcontrol.c:2361
> try_charge_memcg+0x6d0/0xd10 mm/memcontrol.c:2703
> try_charge mm/memcontrol.c:2837 [inline]
> mem_cgroup_charge_skmem+0x51/0x140 mm/memcontrol.c:7290
> sock_reserve_memory+0xb1/0x390 net/core/sock.c:1025
> sk_setsockopt+0x800/0x1e70 net/core/sock.c:1525
> udp_lib_setsockopt+0x99/0x6c0 net/ipv4/udp.c:2692
> udp_setsockopt+0x73/0xa0 net/ipv4/udp.c:2817
> sock_common_setsockopt+0x61/0x70 net/core/sock.c:3668
> __sys_setsockopt+0x1c3/0x230 net/socket.c:2271
> __do_sys_setsockopt net/socket.c:2282 [inline]
> __se_sys_setsockopt net/socket.c:2279 [inline]
> __x64_sys_setsockopt+0x66/0x80 net/socket.c:2279
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> value changed: 0xffff8881382d52c0 -> 0xffff888138893740
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 19632 Comm: syz-executor.0 Not tainted 6.3.0-rc2-syzkaller-00387-g534293368afa #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
>
> Fix it by using READ_ONCE()/WRITE_ONCE() for all accesses to
> stock->cached_objcg.
I believe all read accesses other than obj_stock_flush_required() are
done under the lock, so READ_ONCE() wouldn't be needed AFAICT. Having
READ_ONCE() only around the racy read can be useful to document the
racy read and differentiate it from others.
With that said, it's also inconvenient to keep track moving forward of
which reading sites are racy, and it may be simpler to just annotate
all readers with READ_ONCE().
I am not sure which approach is better, just thinking out loud.
>
> Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
> Reported-by: [email protected]
> Reported-by: Dmitry Vyukov <[email protected]>
> Link:
> https://lore.kernel.org/linux-mm/CACT4Y+ZfucZhM60YPphWiCLJr6+SGFhT+jjm8k1P-a_8Kkxsjg@mail.gmail.com/T/#t
> Signed-off-by: Roman Gushchin <[email protected]>
With the above said, I don't feel strongly either way, the patch looks
good AFAICT:
Reviewed-by: Yosry Ahmed <[email protected]>
> Cc: Yosry Ahmed <[email protected]>
> Cc: Shakeel Butt <[email protected]>
> ---
> mm/memcontrol.c | 19 ++++++++++---------
> 1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 4b27e245a055..c823c35c2ed4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3208,12 +3208,12 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
> * accumulating over a page of vmstat data or when pgdat or idx
> * changes.
> */
> - if (stock->cached_objcg != objcg) {
> + if (READ_ONCE(stock->cached_objcg) != objcg) {
> old = drain_obj_stock(stock);
> obj_cgroup_get(objcg);
> stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
> ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
> - stock->cached_objcg = objcg;
> + WRITE_ONCE(stock->cached_objcg, objcg);
> stock->cached_pgdat = pgdat;
> } else if (stock->cached_pgdat != pgdat) {
> /* Flush the existing cached vmstat data */
> @@ -3267,7 +3267,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
> local_lock_irqsave(&memcg_stock.stock_lock, flags);
>
> stock = this_cpu_ptr(&memcg_stock);
> - if (objcg == stock->cached_objcg && stock->nr_bytes >= nr_bytes) {
> + if (objcg == READ_ONCE(stock->cached_objcg) && stock->nr_bytes >= nr_bytes) {
> stock->nr_bytes -= nr_bytes;
> ret = true;
> }
> @@ -3279,7 +3279,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
>
> static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock)
> {
> - struct obj_cgroup *old = stock->cached_objcg;
> + struct obj_cgroup *old = READ_ONCE(stock->cached_objcg);
>
> if (!old)
> return NULL;
> @@ -3332,7 +3332,7 @@ static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock)
> stock->cached_pgdat = NULL;
> }
>
> - stock->cached_objcg = NULL;
> + WRITE_ONCE(stock->cached_objcg, NULL);
> /*
> * The `old' objects needs to be released by the caller via
> * obj_cgroup_put() outside of memcg_stock_pcp::stock_lock.
> @@ -3343,10 +3343,11 @@ static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock)
> static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
> struct mem_cgroup *root_memcg)
> {
> + struct obj_cgroup *objcg = READ_ONCE(stock->cached_objcg);
> struct mem_cgroup *memcg;
>
> - if (stock->cached_objcg) {
> - memcg = obj_cgroup_memcg(stock->cached_objcg);
> + if (objcg) {
> + memcg = obj_cgroup_memcg(objcg);
> if (memcg && mem_cgroup_is_descendant(memcg, root_memcg))
> return true;
> }
> @@ -3365,10 +3366,10 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
> local_lock_irqsave(&memcg_stock.stock_lock, flags);
>
> stock = this_cpu_ptr(&memcg_stock);
> - if (stock->cached_objcg != objcg) { /* reset if necessary */
> + if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */
> old = drain_obj_stock(stock);
> obj_cgroup_get(objcg);
> - stock->cached_objcg = objcg;
> + WRITE_ONCE(stock->cached_objcg, objcg);
> stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
> ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
> allow_uncharge = true; /* Allow uncharge when objcg changes */
> --
> 2.40.1
>
On Tue, May 02, 2023 at 01:15:02PM -0700, Yosry Ahmed wrote:
> On Tue, May 2, 2023 at 9:09 AM Roman Gushchin <[email protected]> wrote:
> >
> > KCSAN found an issue in obj_stock_flush_required():
> > stock->cached_objcg can be reset between the check and dereference:
> >
> > ==================================================================
> > BUG: KCSAN: data-race in drain_all_stock / drain_obj_stock
> >
> > write to 0xffff888237c2a2f8 of 8 bytes by task 19625 on cpu 0:
> > drain_obj_stock+0x408/0x4e0 mm/memcontrol.c:3306
> > refill_obj_stock+0x9c/0x1e0 mm/memcontrol.c:3340
> > obj_cgroup_uncharge+0xe/0x10 mm/memcontrol.c:3408
> > memcg_slab_free_hook mm/slab.h:587 [inline]
> > __cache_free mm/slab.c:3373 [inline]
> > __do_kmem_cache_free mm/slab.c:3577 [inline]
> > kmem_cache_free+0x105/0x280 mm/slab.c:3602
> > __d_free fs/dcache.c:298 [inline]
> > dentry_free fs/dcache.c:375 [inline]
> > __dentry_kill+0x422/0x4a0 fs/dcache.c:621
> > dentry_kill+0x8d/0x1e0
> > dput+0x118/0x1f0 fs/dcache.c:913
> > __fput+0x3bf/0x570 fs/file_table.c:329
> > ____fput+0x15/0x20 fs/file_table.c:349
> > task_work_run+0x123/0x160 kernel/task_work.c:179
> > resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
> > exit_to_user_mode_loop+0xcf/0xe0 kernel/entry/common.c:171
> > exit_to_user_mode_prepare+0x6a/0xa0 kernel/entry/common.c:203
> > __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
> > syscall_exit_to_user_mode+0x26/0x140 kernel/entry/common.c:296
> > do_syscall_64+0x4d/0xc0 arch/x86/entry/common.c:86
> > entry_SYSCALL_64_after_hwframe+0x63/0xcd
> >
> > read to 0xffff888237c2a2f8 of 8 bytes by task 19632 on cpu 1:
> > obj_stock_flush_required mm/memcontrol.c:3319 [inline]
> > drain_all_stock+0x174/0x2a0 mm/memcontrol.c:2361
> > try_charge_memcg+0x6d0/0xd10 mm/memcontrol.c:2703
> > try_charge mm/memcontrol.c:2837 [inline]
> > mem_cgroup_charge_skmem+0x51/0x140 mm/memcontrol.c:7290
> > sock_reserve_memory+0xb1/0x390 net/core/sock.c:1025
> > sk_setsockopt+0x800/0x1e70 net/core/sock.c:1525
> > udp_lib_setsockopt+0x99/0x6c0 net/ipv4/udp.c:2692
> > udp_setsockopt+0x73/0xa0 net/ipv4/udp.c:2817
> > sock_common_setsockopt+0x61/0x70 net/core/sock.c:3668
> > __sys_setsockopt+0x1c3/0x230 net/socket.c:2271
> > __do_sys_setsockopt net/socket.c:2282 [inline]
> > __se_sys_setsockopt net/socket.c:2279 [inline]
> > __x64_sys_setsockopt+0x66/0x80 net/socket.c:2279
> > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
> > entry_SYSCALL_64_after_hwframe+0x63/0xcd
> >
> > value changed: 0xffff8881382d52c0 -> 0xffff888138893740
> >
> > Reported by Kernel Concurrency Sanitizer on:
> > CPU: 1 PID: 19632 Comm: syz-executor.0 Not tainted 6.3.0-rc2-syzkaller-00387-g534293368afa #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
> >
> > Fix it by using READ_ONCE()/WRITE_ONCE() for all accesses to
> > stock->cached_objcg.
>
> I believe all read accesses other than obj_stock_flush_required() are
> done under the lock, so READ_ONCE() wouldn't be needed AFAICT. Having
> READ_ONCE() only around the racy read can be useful to document the
> racy read and differentiate it from others.
>
> With that said, it's also inconvenient to keep track moving forward of
> which reading sites are racy, and it may be simpler to just annotate
> all readers with READ_ONCE().
>
> I am not sure which approach is better, just thinking out loud.
Yeah, I wasn't sure either. I believe that all changes except the original
READ_ONCE() are not leading to any meaningful asm changes, so it's a matter
of taste.
The reason why I went with the "change them all" approach:
reads without READ_ONCE() and subsequent writes with WRITE_ONCE()
inside a single function looked really weird.
>
> >
> > Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
> > Reported-by: [email protected]
> > Reported-by: Dmitry Vyukov <[email protected]>
> > Link:
> > https://lore.kernel.org/linux-mm/CACT4Y+ZfucZhM60YPphWiCLJr6+SGFhT+jjm8k1P-a_8Kkxsjg@mail.gmail.com/T/#t
> > Signed-off-by: Roman Gushchin <[email protected]>
>
> With the above said, I don't feel strongly either way, the patch looks
> good AFAICT:
> Reviewed-by: Yosry Ahmed <[email protected]>
Thanks!
On Tue, May 2, 2023 at 2:38 PM Roman Gushchin <[email protected]> wrote:
>
> On Tue, May 02, 2023 at 01:15:02PM -0700, Yosry Ahmed wrote:
> > On Tue, May 2, 2023 at 9:09 AM Roman Gushchin <[email protected]> wrote:
> > >
> > > KCSAN found an issue in obj_stock_flush_required():
> > > stock->cached_objcg can be reset between the check and dereference:
> > >
> > > ==================================================================
> > > BUG: KCSAN: data-race in drain_all_stock / drain_obj_stock
> > >
> > > write to 0xffff888237c2a2f8 of 8 bytes by task 19625 on cpu 0:
> > > drain_obj_stock+0x408/0x4e0 mm/memcontrol.c:3306
> > > refill_obj_stock+0x9c/0x1e0 mm/memcontrol.c:3340
> > > obj_cgroup_uncharge+0xe/0x10 mm/memcontrol.c:3408
> > > memcg_slab_free_hook mm/slab.h:587 [inline]
> > > __cache_free mm/slab.c:3373 [inline]
> > > __do_kmem_cache_free mm/slab.c:3577 [inline]
> > > kmem_cache_free+0x105/0x280 mm/slab.c:3602
> > > __d_free fs/dcache.c:298 [inline]
> > > dentry_free fs/dcache.c:375 [inline]
> > > __dentry_kill+0x422/0x4a0 fs/dcache.c:621
> > > dentry_kill+0x8d/0x1e0
> > > dput+0x118/0x1f0 fs/dcache.c:913
> > > __fput+0x3bf/0x570 fs/file_table.c:329
> > > ____fput+0x15/0x20 fs/file_table.c:349
> > > task_work_run+0x123/0x160 kernel/task_work.c:179
> > > resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
> > > exit_to_user_mode_loop+0xcf/0xe0 kernel/entry/common.c:171
> > > exit_to_user_mode_prepare+0x6a/0xa0 kernel/entry/common.c:203
> > > __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
> > > syscall_exit_to_user_mode+0x26/0x140 kernel/entry/common.c:296
> > > do_syscall_64+0x4d/0xc0 arch/x86/entry/common.c:86
> > > entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > >
> > > read to 0xffff888237c2a2f8 of 8 bytes by task 19632 on cpu 1:
> > > obj_stock_flush_required mm/memcontrol.c:3319 [inline]
> > > drain_all_stock+0x174/0x2a0 mm/memcontrol.c:2361
> > > try_charge_memcg+0x6d0/0xd10 mm/memcontrol.c:2703
> > > try_charge mm/memcontrol.c:2837 [inline]
> > > mem_cgroup_charge_skmem+0x51/0x140 mm/memcontrol.c:7290
> > > sock_reserve_memory+0xb1/0x390 net/core/sock.c:1025
> > > sk_setsockopt+0x800/0x1e70 net/core/sock.c:1525
> > > udp_lib_setsockopt+0x99/0x6c0 net/ipv4/udp.c:2692
> > > udp_setsockopt+0x73/0xa0 net/ipv4/udp.c:2817
> > > sock_common_setsockopt+0x61/0x70 net/core/sock.c:3668
> > > __sys_setsockopt+0x1c3/0x230 net/socket.c:2271
> > > __do_sys_setsockopt net/socket.c:2282 [inline]
> > > __se_sys_setsockopt net/socket.c:2279 [inline]
> > > __x64_sys_setsockopt+0x66/0x80 net/socket.c:2279
> > > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > > do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
> > > entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > >
> > > value changed: 0xffff8881382d52c0 -> 0xffff888138893740
> > >
> > > Reported by Kernel Concurrency Sanitizer on:
> > > CPU: 1 PID: 19632 Comm: syz-executor.0 Not tainted 6.3.0-rc2-syzkaller-00387-g534293368afa #0
> > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
> > >
> > > Fix it by using READ_ONCE()/WRITE_ONCE() for all accesses to
> > > stock->cached_objcg.
> >
> > I believe all read accesses other than obj_stock_flush_required() are
> > done under the lock, so READ_ONCE() wouldn't be needed AFAICT. Having
> > READ_ONCE() only around the racy read can be useful to document the
> > racy read and differentiate it from others.
> >
> > With that said, it's also inconvenient to keep track moving forward of
> > which reading sites are racy, and it may be simpler to just annotate
> > all readers with READ_ONCE().
> >
> > I am not sure which approach is better, just thinking out loud.
>
> Yeah, I wasn't sure either. I believe that all changes except the original
> READ_ONCE() are not leading to any meaningful asm changes, so it's a matter
> of taste.
>
> The reason why I went with the "change them all" approach:
> reads without READ_ONCE() and subsequent writes with WRITE_ONCE()
> inside a single function looked really weird.
>
Agreed. It might be worth adding a comment somewhere documenting this.
It's not very hard to dig though, so whatever you think is best.
> >
> > >
> > > Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
> > > Reported-by: [email protected]
> > > Reported-by: Dmitry Vyukov <[email protected]>
> > > Link:
> > > https://lore.kernel.org/linux-mm/CACT4Y+ZfucZhM60YPphWiCLJr6+SGFhT+jjm8k1P-a_8Kkxsjg@mail.gmail.com/T/#t
> > > Signed-off-by: Roman Gushchin <[email protected]>
> >
> > With the above said, I don't feel strongly either way, the patch looks
> > good AFAICT:
> > Reviewed-by: Yosry Ahmed <[email protected]>
>
> Thanks!
On Tue, 2 May 2023 at 18:09, Roman Gushchin <[email protected]> wrote:
>
> KCSAN found an issue in obj_stock_flush_required():
> stock->cached_objcg can be reset between the check and dereference:
>
> ==================================================================
> BUG: KCSAN: data-race in drain_all_stock / drain_obj_stock
>
> write to 0xffff888237c2a2f8 of 8 bytes by task 19625 on cpu 0:
> drain_obj_stock+0x408/0x4e0 mm/memcontrol.c:3306
> refill_obj_stock+0x9c/0x1e0 mm/memcontrol.c:3340
> obj_cgroup_uncharge+0xe/0x10 mm/memcontrol.c:3408
> memcg_slab_free_hook mm/slab.h:587 [inline]
> __cache_free mm/slab.c:3373 [inline]
> __do_kmem_cache_free mm/slab.c:3577 [inline]
> kmem_cache_free+0x105/0x280 mm/slab.c:3602
> __d_free fs/dcache.c:298 [inline]
> dentry_free fs/dcache.c:375 [inline]
> __dentry_kill+0x422/0x4a0 fs/dcache.c:621
> dentry_kill+0x8d/0x1e0
> dput+0x118/0x1f0 fs/dcache.c:913
> __fput+0x3bf/0x570 fs/file_table.c:329
> ____fput+0x15/0x20 fs/file_table.c:349
> task_work_run+0x123/0x160 kernel/task_work.c:179
> resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
> exit_to_user_mode_loop+0xcf/0xe0 kernel/entry/common.c:171
> exit_to_user_mode_prepare+0x6a/0xa0 kernel/entry/common.c:203
> __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
> syscall_exit_to_user_mode+0x26/0x140 kernel/entry/common.c:296
> do_syscall_64+0x4d/0xc0 arch/x86/entry/common.c:86
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> read to 0xffff888237c2a2f8 of 8 bytes by task 19632 on cpu 1:
> obj_stock_flush_required mm/memcontrol.c:3319 [inline]
> drain_all_stock+0x174/0x2a0 mm/memcontrol.c:2361
> try_charge_memcg+0x6d0/0xd10 mm/memcontrol.c:2703
> try_charge mm/memcontrol.c:2837 [inline]
> mem_cgroup_charge_skmem+0x51/0x140 mm/memcontrol.c:7290
> sock_reserve_memory+0xb1/0x390 net/core/sock.c:1025
> sk_setsockopt+0x800/0x1e70 net/core/sock.c:1525
> udp_lib_setsockopt+0x99/0x6c0 net/ipv4/udp.c:2692
> udp_setsockopt+0x73/0xa0 net/ipv4/udp.c:2817
> sock_common_setsockopt+0x61/0x70 net/core/sock.c:3668
> __sys_setsockopt+0x1c3/0x230 net/socket.c:2271
> __do_sys_setsockopt net/socket.c:2282 [inline]
> __se_sys_setsockopt net/socket.c:2279 [inline]
> __x64_sys_setsockopt+0x66/0x80 net/socket.c:2279
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> value changed: 0xffff8881382d52c0 -> 0xffff888138893740
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 19632 Comm: syz-executor.0 Not tainted 6.3.0-rc2-syzkaller-00387-g534293368afa #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
>
> Fix it by using READ_ONCE()/WRITE_ONCE() for all accesses to
> stock->cached_objcg.
>
> Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
> Reported-by: [email protected]
> Reported-by: Dmitry Vyukov <[email protected]>
> Link:
> https://lore.kernel.org/linux-mm/CACT4Y+ZfucZhM60YPphWiCLJr6+SGFhT+jjm8k1P-a_8Kkxsjg@mail.gmail.com/T/#t
> Signed-off-by: Roman Gushchin <[email protected]>
> Cc: Yosry Ahmed <[email protected]>
> Cc: Shakeel Butt <[email protected]>
> ---
> mm/memcontrol.c | 19 ++++++++++---------
> 1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 4b27e245a055..c823c35c2ed4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3208,12 +3208,12 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
> * accumulating over a page of vmstat data or when pgdat or idx
> * changes.
> */
> - if (stock->cached_objcg != objcg) {
> + if (READ_ONCE(stock->cached_objcg) != objcg) {
> old = drain_obj_stock(stock);
> obj_cgroup_get(objcg);
> stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
> ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
> - stock->cached_objcg = objcg;
> + WRITE_ONCE(stock->cached_objcg, objcg);
> stock->cached_pgdat = pgdat;
> } else if (stock->cached_pgdat != pgdat) {
> /* Flush the existing cached vmstat data */
> @@ -3267,7 +3267,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
> local_lock_irqsave(&memcg_stock.stock_lock, flags);
>
> stock = this_cpu_ptr(&memcg_stock);
> - if (objcg == stock->cached_objcg && stock->nr_bytes >= nr_bytes) {
> + if (objcg == READ_ONCE(stock->cached_objcg) && stock->nr_bytes >= nr_bytes) {
> stock->nr_bytes -= nr_bytes;
> ret = true;
> }
> @@ -3279,7 +3279,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
>
> static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock)
> {
> - struct obj_cgroup *old = stock->cached_objcg;
> + struct obj_cgroup *old = READ_ONCE(stock->cached_objcg);
>
> if (!old)
> return NULL;
> @@ -3332,7 +3332,7 @@ static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock)
> stock->cached_pgdat = NULL;
> }
>
> - stock->cached_objcg = NULL;
> + WRITE_ONCE(stock->cached_objcg, NULL);
> /*
> * The `old' objects needs to be released by the caller via
> * obj_cgroup_put() outside of memcg_stock_pcp::stock_lock.
> @@ -3343,10 +3343,11 @@ static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock)
> static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
> struct mem_cgroup *root_memcg)
> {
> + struct obj_cgroup *objcg = READ_ONCE(stock->cached_objcg);
> struct mem_cgroup *memcg;
>
> - if (stock->cached_objcg) {
> - memcg = obj_cgroup_memcg(stock->cached_objcg);
> + if (objcg) {
> + memcg = obj_cgroup_memcg(objcg);
> if (memcg && mem_cgroup_is_descendant(memcg, root_memcg))
> return true;
> }
> @@ -3365,10 +3366,10 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
> local_lock_irqsave(&memcg_stock.stock_lock, flags);
>
> stock = this_cpu_ptr(&memcg_stock);
> - if (stock->cached_objcg != objcg) { /* reset if necessary */
> + if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */
> old = drain_obj_stock(stock);
> obj_cgroup_get(objcg);
> - stock->cached_objcg = objcg;
> + WRITE_ONCE(stock->cached_objcg, objcg);
> stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
> ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
> allow_uncharge = true; /* Allow uncharge when objcg changes */
Reviewed-by: Dmitry Vyukov <[email protected]>
On Tue, May 02, 2023 at 02:38:19PM -0700, Roman Gushchin wrote:
[...]
> >
> > I believe all read accesses other than obj_stock_flush_required() are
> > done under the lock, so READ_ONCE() wouldn't be needed AFAICT. Having
> > READ_ONCE() only around the racy read can be useful to document the
> > racy read and differentiate it from others.
> >
> > With that said, it's also inconvenient to keep track moving forward of
> > which reading sites are racy, and it may be simpler to just annotate
> > all readers with READ_ONCE().
> >
> > I am not sure which approach is better, just thinking out loud.
>
> Yeah, I wasn't sure either. I believe that all changes except the original
> READ_ONCE() are not leading to any meaningful asm changes, so it's a matter
> of taste.
>
> The reason why I went with the "change them all" approach:
> reads without READ_ONCE() and subsequent writes with WRITE_ONCE()
> inside a single function looked really weird.
>
Change them all is the right approach. This code will evolve in future
and having partial tagging will cause confusion or might be missed
altogether. Also the automated tools prefer change them all.
On Tue, May 02, 2023 at 09:08:38AM -0700, Roman Gushchin wrote:
> KCSAN found an issue in obj_stock_flush_required():
> stock->cached_objcg can be reset between the check and dereference:
>
> ==================================================================
> BUG: KCSAN: data-race in drain_all_stock / drain_obj_stock
>
> write to 0xffff888237c2a2f8 of 8 bytes by task 19625 on cpu 0:
> drain_obj_stock+0x408/0x4e0 mm/memcontrol.c:3306
> refill_obj_stock+0x9c/0x1e0 mm/memcontrol.c:3340
> obj_cgroup_uncharge+0xe/0x10 mm/memcontrol.c:3408
> memcg_slab_free_hook mm/slab.h:587 [inline]
> __cache_free mm/slab.c:3373 [inline]
> __do_kmem_cache_free mm/slab.c:3577 [inline]
> kmem_cache_free+0x105/0x280 mm/slab.c:3602
> __d_free fs/dcache.c:298 [inline]
> dentry_free fs/dcache.c:375 [inline]
> __dentry_kill+0x422/0x4a0 fs/dcache.c:621
> dentry_kill+0x8d/0x1e0
> dput+0x118/0x1f0 fs/dcache.c:913
> __fput+0x3bf/0x570 fs/file_table.c:329
> ____fput+0x15/0x20 fs/file_table.c:349
> task_work_run+0x123/0x160 kernel/task_work.c:179
> resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
> exit_to_user_mode_loop+0xcf/0xe0 kernel/entry/common.c:171
> exit_to_user_mode_prepare+0x6a/0xa0 kernel/entry/common.c:203
> __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
> syscall_exit_to_user_mode+0x26/0x140 kernel/entry/common.c:296
> do_syscall_64+0x4d/0xc0 arch/x86/entry/common.c:86
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> read to 0xffff888237c2a2f8 of 8 bytes by task 19632 on cpu 1:
> obj_stock_flush_required mm/memcontrol.c:3319 [inline]
> drain_all_stock+0x174/0x2a0 mm/memcontrol.c:2361
> try_charge_memcg+0x6d0/0xd10 mm/memcontrol.c:2703
> try_charge mm/memcontrol.c:2837 [inline]
> mem_cgroup_charge_skmem+0x51/0x140 mm/memcontrol.c:7290
> sock_reserve_memory+0xb1/0x390 net/core/sock.c:1025
> sk_setsockopt+0x800/0x1e70 net/core/sock.c:1525
> udp_lib_setsockopt+0x99/0x6c0 net/ipv4/udp.c:2692
> udp_setsockopt+0x73/0xa0 net/ipv4/udp.c:2817
> sock_common_setsockopt+0x61/0x70 net/core/sock.c:3668
> __sys_setsockopt+0x1c3/0x230 net/socket.c:2271
> __do_sys_setsockopt net/socket.c:2282 [inline]
> __se_sys_setsockopt net/socket.c:2279 [inline]
> __x64_sys_setsockopt+0x66/0x80 net/socket.c:2279
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> value changed: 0xffff8881382d52c0 -> 0xffff888138893740
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 19632 Comm: syz-executor.0 Not tainted 6.3.0-rc2-syzkaller-00387-g534293368afa #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
>
> Fix it by using READ_ONCE()/WRITE_ONCE() for all accesses to
> stock->cached_objcg.
>
> Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
> Reported-by: [email protected]
> Reported-by: Dmitry Vyukov <[email protected]>
> Link:
> https://lore.kernel.org/linux-mm/CACT4Y+ZfucZhM60YPphWiCLJr6+SGFhT+jjm8k1P-a_8Kkxsjg@mail.gmail.com/T/#t
> Signed-off-by: Roman Gushchin <[email protected]>
> Cc: Yosry Ahmed <[email protected]>
> Cc: Shakeel Butt <[email protected]>
Acked-by: Shakeel Butt <[email protected]>