From: Michal Hocko <mhocko@xxxxxxxx>
Subject: mm, memcg: remove hotplug locking from try_charge
The following lockdep splat has been noticed during LTP testing
[21002.630252] ======================================================
[21002.637148] WARNING: possible circular locking dependency detected
[21002.644045] 4.13.0-rc3-next-20170807 #12 Not tainted
[21002.649583] ------------------------------------------------------
[21002.656492] a.out/4771 is trying to acquire lock:
[21002.661742] (cpu_hotplug_lock.rw_sem){++++++}, at: [<ffffffff812b4668>] drain_all_stock.part.35+0x18/0x140
[21002.672629]
[21002.672629] but task is already holding lock:
[21002.679137] (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530
[21002.688371]
[21002.688371] which lock already depends on the new lock.
[21002.688371]
[21002.697505]
[21002.697505] the existing dependency chain (in reverse order) is:
[21002.705856]
[21002.705856] -> #3 (&mm->mmap_sem){++++++}:
[21002.712080] lock_acquire+0xc9/0x230
[21002.716661] __might_fault+0x70/0xa0
[21002.721241] _copy_to_user+0x23/0x70
[21002.725814] filldir+0xa7/0x110
[21002.729988] xfs_dir2_sf_getdents.isra.10+0x20c/0x2c0 [xfs]
[21002.736840] xfs_readdir+0x1fa/0x2c0 [xfs]
[21002.742042] xfs_file_readdir+0x30/0x40 [xfs]
[21002.747485] iterate_dir+0x17a/0x1a0
[21002.752057] SyS_getdents+0xb0/0x160
[21002.756638] entry_SYSCALL_64_fastpath+0x1f/0xbe
[21002.762371]
[21002.762371] -> #2 (&type->i_mutex_dir_key#3){++++++}:
[21002.769661] lock_acquire+0xc9/0x230
[21002.774239] down_read+0x51/0xb0
[21002.778429] lookup_slow+0xde/0x210
[21002.782903] walk_component+0x160/0x250
[21002.787765] link_path_walk+0x1a6/0x610
[21002.792625] path_openat+0xe4/0xd50
[21002.797100] do_filp_open+0x91/0x100
[21002.801673] file_open_name+0xf5/0x130
[21002.806429] filp_open+0x33/0x50
[21002.810620] kernel_read_file_from_path+0x39/0x80
[21002.816459] _request_firmware+0x39f/0x880
[21002.821610] request_firmware_direct+0x37/0x50
[21002.827151] request_microcode_fw+0x64/0xe0
[21002.832401] reload_store+0xf7/0x180
[21002.836974] dev_attr_store+0x18/0x30
[21002.841641] sysfs_kf_write+0x44/0x60
[21002.846318] kernfs_fop_write+0x113/0x1a0
[21002.851374] __vfs_write+0x37/0x170
[21002.855849] vfs_write+0xc7/0x1c0
[21002.860128] SyS_write+0x58/0xc0
[21002.864313] do_syscall_64+0x6c/0x1f0
[21002.868973] return_from_SYSCALL_64+0x0/0x7a
[21002.874317]
[21002.874317] -> #1 (microcode_mutex){+.+.+.}:
[21002.880748] lock_acquire+0xc9/0x230
[21002.885322] __mutex_lock+0x88/0x960
[21002.889894] mutex_lock_nested+0x1b/0x20
[21002.894854] microcode_init+0xbb/0x208
[21002.899617] do_one_initcall+0x51/0x1a9
[21002.904481] kernel_init_freeable+0x208/0x2a7
[21002.909922] kernel_init+0xe/0x104
[21002.914298] ret_from_fork+0x2a/0x40
[21002.918867]
[21002.918867] -> #0 (cpu_hotplug_lock.rw_sem){++++++}:
[21002.926058] __lock_acquire+0x153c/0x1550
[21002.931112] lock_acquire+0xc9/0x230
[21002.935688] cpus_read_lock+0x4b/0x90
[21002.940353] drain_all_stock.part.35+0x18/0x140
[21002.945987] try_charge+0x3ab/0x6e0
[21002.950460] mem_cgroup_try_charge+0x7f/0x2c0
[21002.955902] shmem_getpage_gfp+0x25f/0x1050
[21002.961149] shmem_fault+0x96/0x200
[21002.965621] __do_fault+0x1e/0xa0
[21002.969905] __handle_mm_fault+0x9c3/0xe00
[21002.975056] handle_mm_fault+0x16e/0x380
[21002.980013] __do_page_fault+0x24a/0x530
[21002.984968] do_page_fault+0x30/0x80
[21002.989537] page_fault+0x28/0x30
[21002.993812]
[21002.993812] other info that might help us debug this:
[21002.993812]
[21003.002744] Chain exists of:
[21003.002744] cpu_hotplug_lock.rw_sem --> &type->i_mutex_dir_key#3 --> &mm->mmap_sem
[21003.002744]
[21003.016238] Possible unsafe locking scenario:
[21003.016238]
[21003.022843] CPU0 CPU1
[21003.027896] ---- ----
[21003.032948] lock(&mm->mmap_sem);
[21003.036741] lock(&type->i_mutex_dir_key#3);
[21003.044419] lock(&mm->mmap_sem);
[21003.051025] lock(cpu_hotplug_lock.rw_sem);
[21003.055788]
[21003.055788] *** DEADLOCK ***
[21003.055788]
[21003.062393] 2 locks held by a.out/4771:
[21003.066675] #0: (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530
[21003.076391] #1: (percpu_charge_mutex){+.+...}, at: [<ffffffff812b4c97>] try_charge+0x397/0x6e0
The problem is very similar to the one fixed by a459eeb7b852 ("mm,
page_alloc: do not depend on cpu hotplug locks inside the allocator"). We
are taking hotplug locks while we can be sitting on top of basically
arbitrary locks. This just calls for problems.
We can get rid of {get,put}_online_cpus, fortunately. We do not have to
be worried about races with memory hotplug because drain_local_stock,
which is called from both the WQ draining and the memory hotplug contexts,
is always operating on the local cpu stock with IRQs disabled.
The only thing to be careful about is that the target memcg doesn't vanish
while we are still in drain_all_stock so take a reference on it.
Link: http://lkml.kernel.org/r/20170913090023.28322-1-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Reported-by: Artem Savkov <asavkov@xxxxxxxxxx>
Tested-by: Artem Savkov <asavkov@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
diff -puN mm/memcontrol.c~mm-memcg-remove-hotplug-locking-from-try_charge mm/memcontrol.c
--- a/mm/memcontrol.c~mm-memcg-remove-hotplug-locking-from-try_charge
+++ a/mm/memcontrol.c
@@ -1777,6 +1777,10 @@ static void drain_local_stock(struct wor
struct memcg_stock_pcp *stock;
unsigned long flags;
+ /*
+ * The only protection from memory hotplug vs. drain_stock races is
+ * that we always operate on local CPU stock here with IRQ disabled
+ */
local_irq_save(flags);
stock = this_cpu_ptr(&memcg_stock);
@@ -1821,27 +1825,33 @@ static void drain_all_stock(struct mem_c
/* If someone's already draining, avoid adding running more workers. */
if (!mutex_trylock(&percpu_charge_mutex))
return;
- /* Notify other cpus that system-wide "drain" is running */
- get_online_cpus();
+ /*
+ * Notify other cpus that system-wide "drain" is running
+ * We do not care about races with the cpu hotplug because cpu down
+ * as well as workers from this path always operate on the local
+ * per-cpu data. CPU up doesn't touch memcg_stock at all.
+ */
curcpu = get_cpu();
for_each_online_cpu(cpu) {
struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
struct mem_cgroup *memcg;
memcg = stock->cached;
- if (!memcg || !stock->nr_pages)
+ if (!memcg || !stock->nr_pages || !css_tryget(&memcg->css))
continue;
- if (!mem_cgroup_is_descendant(memcg, root_memcg))
+ if (!mem_cgroup_is_descendant(memcg, root_memcg)) {
+ css_put(&memcg->css);
continue;
+ }
if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) {
if (cpu == curcpu)
drain_local_stock(&stock->work);
else
schedule_work_on(cpu, &stock->work);
}
+ css_put(&memcg->css);
}
put_cpu();
- put_online_cpus();
mutex_unlock(&percpu_charge_mutex);
}
_
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