[PATCH 5.10 002/121] mm: memcg: synchronize objcg lists with a dedicated spinlock

Greg Kroah-Hartman
2022-02-21T09:16:22Z

From: Roman Gushchin <guro@fb.com>

commit 0764db9b49c932b89ee4d9e3236dff4bb07b4a66 upstream.

Alexander reported a circular lock dependency revealed by the mmap1 ltp
test:

LOCKDEP_CIRCULAR (suite: ltp, case: mtest06 (mmap1))
WARNING: possible circular locking dependency detected
5.17.0-20220113.rc0.git0.f2211f194038.300.fc35.s390x+debug #1 Not tainted
------------------------------------------------------
mmap1/202299 is trying to acquire lock:
00000001892c0188 (css_set_lock){..-.}-{2:2}, at: obj_cgroup_release+0x4a/0xe0
but task is already holding lock:
00000000ca3b3818 (&sighand->siglock){-.-.}-{2:2}, at: force_sig_info_to_task+0x38/0x180
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&sighand->siglock){-.-.}-{2:2}:
__lock_acquire+0x604/0xbd8
lock_acquire.part.0+0xe2/0x238
lock_acquire+0xb0/0x200
_raw_spin_lock_irqsave+0x6a/0xd8
__lock_task_sighand+0x90/0x190
cgroup_freeze_task+0x2e/0x90
cgroup_migrate_execute+0x11c/0x608
cgroup_update_dfl_csses+0x246/0x270
cgroup_subtree_control_write+0x238/0x518
kernfs_fop_write_iter+0x13e/0x1e0
new_sync_write+0x100/0x190
vfs_write+0x22c/0x2d8
ksys_write+0x6c/0xf8
__do_syscall+0x1da/0x208
system_call+0x82/0xb0
-> #0 (css_set_lock){..-.}-{2:2}:
check_prev_add+0xe0/0xed8
validate_chain+0x736/0xb20
__lock_acquire+0x604/0xbd8
lock_acquire.part.0+0xe2/0x238
lock_acquire+0xb0/0x200
_raw_spin_lock_irqsave+0x6a/0xd8
obj_cgroup_release+0x4a/0xe0
percpu_ref_put_many.constprop.0+0x150/0x168
drain_obj_stock+0x94/0xe8
refill_obj_stock+0x94/0x278
obj_cgroup_charge+0x164/0x1d8
kmem_cache_alloc+0xac/0x528
__sigqueue_alloc+0x150/0x308
__send_signal+0x260/0x550
send_signal+0x7e/0x348
force_sig_info_to_task+0x104/0x180
force_sig_fault+0x48/0x58
__do_pgm_check+0x120/0x1f0
pgm_check_handler+0x11e/0x180
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&sighand->siglock);
lock(css_set_lock);
lock(&sighand->siglock);
lock(css_set_lock);
*** DEADLOCK ***
2 locks held by mmap1/202299:
#0: 00000000ca3b3818 (&sighand->siglock){-.-.}-{2:2}, at: force_sig_info_to_task+0x38/0x180
#1: 00000001892ad560 (rcu_read_lock){....}-{1:2}, at: percpu_ref_put_many.constprop.0+0x0/0x168
stack backtrace:
CPU: 15 PID: 202299 Comm: mmap1 Not tainted 5.17.0-20220113.rc0.git0.f2211f194038.300.fc35.s390x+debug #1
Hardware name: IBM 3906 M04 704 (LPAR)
Call Trace:
dump_stack_lvl+0x76/0x98
check_noncircular+0x136/0x158
check_prev_add+0xe0/0xed8
validate_chain+0x736/0xb20
__lock_acquire+0x604/0xbd8
lock_acquire.part.0+0xe2/0x238
lock_acquire+0xb0/0x200
_raw_spin_lock_irqsave+0x6a/0xd8
obj_cgroup_release+0x4a/0xe0
percpu_ref_put_many.constprop.0+0x150/0x168
drain_obj_stock+0x94/0xe8
refill_obj_stock+0x94/0x278
obj_cgroup_charge+0x164/0x1d8
kmem_cache_alloc+0xac/0x528
__sigqueue_alloc+0x150/0x308
__send_signal+0x260/0x550
send_signal+0x7e/0x348
force_sig_info_to_task+0x104/0x180
force_sig_fault+0x48/0x58
__do_pgm_check+0x120/0x1f0
pgm_check_handler+0x11e/0x180
INFO: lockdep is turned off.

In this example a slab allocation from __send_signal() caused a
refilling and draining of a percpu objcg stock, resulted in a releasing
of another non-related objcg. Objcg release path requires taking the
css_set_lock, which is used to synchronize objcg lists.

This can create a circular dependency with the sighandler lock, which is
taken with the locked css_set_lock by the freezer code (to freeze a
task).

In general it seems that using css_set_lock to synchronize objcg lists
makes any slab allocations and deallocation with the locked css_set_lock
and any intervened locks risky.

To fix the problem and make the code more robust let's stop using
css_set_lock to synchronize objcg lists and use a new dedicated spinlock
instead.

Link: https://lkml.kernel.org/r/Yfm1IHmoGdyUR81T@carbon.dhcp.thefacebook.com
Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
Signed-off-by: Roman Gushchin <guro@fb.com>
Reported-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Tested-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Jeremy Linton <jeremy.linton@arm.com>
Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/memcontrol.h | 5 +++--
mm/memcontrol.c | 10 +++++-----
2 files changed, 8 insertions(+), 7 deletions(-)

--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -197,7 +197,7 @@ struct obj_cgroup {
struct mem_cgroup *memcg;
atomic_t nr_charged_bytes;
union {
- struct list_head list;
+ struct list_head list; /* protected by objcg_lock */
struct rcu_head rcu;
};
};
@@ -300,7 +300,8 @@ struct mem_cgroup {
int kmemcg_id;
enum memcg_kmem_state kmem_state;
struct obj_cgroup __rcu *objcg;
- struct list_head objcg_list; /* list of inherited objcgs */
+ /* list of inherited objcgs, protected by objcg_lock */
+ struct list_head objcg_list;
#endif

MEMCG_PADDING(_pad2_);
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -250,7 +250,7 @@ struct cgroup_subsys_state *vmpressure_t
}

#ifdef CONFIG_MEMCG_KMEM
-extern spinlock_t css_set_lock;
+static DEFINE_SPINLOCK(objcg_lock);

static void obj_cgroup_release(struct percpu_ref *ref)
{
@@ -284,13 +284,13 @@ static void obj_cgroup_release(struct pe
WARN_ON_ONCE(nr_bytes & (PAGE_SIZE - 1));
nr_pages = nr_bytes >> PAGE_SHIFT;

- spin_lock_irqsave(&css_set_lock, flags);
+ spin_lock_irqsave(&objcg_lock, flags);
memcg = obj_cgroup_memcg(objcg);
if (nr_pages)
__memcg_kmem_uncharge(memcg, nr_pages);
list_del(&objcg->list);
mem_cgroup_put(memcg);
- spin_unlock_irqrestore(&css_set_lock, flags);
+ spin_unlock_irqrestore(&objcg_lock, flags);

percpu_ref_exit(ref);
kfree_rcu(objcg, rcu);
@@ -322,7 +322,7 @@ static void memcg_reparent_objcgs(struct

objcg = rcu_replace_pointer(memcg->objcg, NULL, true);

- spin_lock_irq(&css_set_lock);
+ spin_lock_irq(&objcg_lock);

/* Move active objcg to the parent's list */
xchg(&objcg->memcg, parent);
@@ -337,7 +337,7 @@ static void memcg_reparent_objcgs(struct
}
list_splice(&memcg->objcg_list, &parent->objcg_list);

- spin_unlock_irq(&css_set_lock);
+ spin_unlock_irq(&objcg_lock);

percpu_ref_kill(&objcg->refcnt);
}