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Date: Fri, 20 Jun 2014 11:42:10 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Fengguang Wu <fengguang.wu@...el.com>,
Jet Chen <jet.chen@...el.com>,
Yuanhan Liu <yuanhan.liu@...el.com>, LKP <lkp@...org>,
cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [memcontrol] WARNING: CPU: 0 PID: 1 at kernel/res_counter.c:28
res_counter_uncharge_locked()
On Fri, Jun 20, 2014 at 06:27:04PM +0800, Fengguang Wu wrote:
> Greetings,
>
> 0day kernel testing robot got the below dmesg and the first bad commit is
>
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
Thanks for the bisect.
> commit ddc5bfec501f4be3f9e89084c2db270c0c45d1d6
> Author: Johannes Weiner <hannes@...xchg.org>
> AuthorDate: Fri Jun 20 10:27:58 2014 +1000
> Commit: Stephen Rothwell <sfr@...b.auug.org.au>
> CommitDate: Fri Jun 20 10:27:58 2014 +1000
>
> mm: memcontrol: rewrite uncharge API
>
> The memcg uncharging code that is involved towards the end of a page's
> lifetime - truncation, reclaim, swapout, migration - is impressively
> complicated and fragile.
>
> Because anonymous and file pages were always charged before they had their
> page->mapping established, uncharges had to happen when the page type
> could still be known from the context; as in unmap for anonymous, page
> cache removal for file and shmem pages, and swap cache truncation for swap
> pages. However, these operations happen well before the page is actually
> freed, and so a lot of synchronization is necessary:
>
> - Charging, uncharging, page migration, and charge migration all need
> to take a per-page bit spinlock as they could race with uncharging.
>
> - Swap cache truncation happens during both swap-in and swap-out, and
> possibly repeatedly before the page is actually freed. This means
> that the memcg swapout code is called from many contexts that make
> no sense and it has to figure out the direction from page state to
> make sure memory and memory+swap are always correctly charged.
>
> - On page migration, the old page might be unmapped but then reused,
> so memcg code has to prevent untimely uncharging in that case.
> Because this code - which should be a simple charge transfer - is so
> special-cased, it is not reusable for replace_page_cache().
>
> But now that charged pages always have a page->mapping, introduce
> mem_cgroup_uncharge(), which is called after the final put_page(), when we
> know for sure that nobody is looking at the page anymore.
>
> For page migration, introduce mem_cgroup_migrate(), which is called after
> the migration is successful and the new page is fully rmapped. Because
> the old page is no longer uncharged after migration, prevent double
> charges by decoupling the page's memcg association (PCG_USED and
> pc->mem_cgroup) from the page holding an actual charge. The new bits
> PCG_MEM and PCG_MEMSW represent the respective charges and are transferred
> to the new page during migration.
>
> mem_cgroup_migrate() is suitable for replace_page_cache() as well, which
> gets rid of mem_cgroup_replace_page_cache().
>
> Swap accounting is massively simplified: because the page is no longer
> uncharged as early as swap cache deletion, a new mem_cgroup_swapout() can
> transfer the page's memory+swap charge (PCG_MEMSW) to the swap entry
> before the final put_page() in page reclaim.
>
> Finally, page_cgroup changes are now protected by whatever protection the
> page itself offers: anonymous pages are charged under the page table lock,
> whereas page cache insertions, swapin, and migration hold the page lock.
> Uncharging happens under full exclusion with no outstanding references.
> Charging and uncharging also ensure that the page is off-LRU, which
> serializes against charge migration. Remove the very costly page_cgroup
> lock and set pc->flags non-atomically.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.cz>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Vladimir Davydov <vdavydov@...allels.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>
> +-----------------------------------------------------------------------+------------+------------+---------------+
> | | 5b647620c6 | ddc5bfec50 | next-20140620 |
> +-----------------------------------------------------------------------+------------+------------+---------------+
> | boot_successes | 60 | 0 | 0 |
> | boot_failures | 0 | 20 | 13 |
> | WARNING:CPU:PID:at_kernel/res_counter.c:res_counter_uncharge_locked() | 0 | 20 | 13 |
> | backtrace:vm_munmap | 0 | 20 | 13 |
> | backtrace:SyS_munmap | 0 | 20 | 13 |
> | backtrace:do_sys_open | 0 | 20 | 13 |
> | backtrace:SyS_open | 0 | 20 | 13 |
> | backtrace:do_execve | 0 | 20 | 13 |
> | backtrace:SyS_execve | 0 | 20 | 13 |
> | backtrace:do_group_exit | 0 | 20 | 13 |
> | backtrace:SyS_exit_group | 0 | 20 | 13 |
> | backtrace:SYSC_renameat2 | 0 | 11 | 8 |
> | backtrace:SyS_rename | 0 | 11 | 8 |
> | backtrace:do_munmap | 0 | 11 | 8 |
> | backtrace:SyS_brk | 0 | 11 | 8 |
> | Out_of_memory:Kill_process | 0 | 1 | |
> | backtrace:do_unlinkat | 0 | 9 | 5 |
> | backtrace:SyS_unlink | 0 | 9 | 5 |
> | backtrace:SYSC_umount | 0 | 9 | |
> | backtrace:SyS_umount | 0 | 9 | |
> | backtrace:cleanup_mnt_work | 0 | 0 | 5 |
> +-----------------------------------------------------------------------+------------+------------+---------------+
>
> [ 2.747397] debug: unmapping init [mem 0xffff880001a3a000-0xffff880001bfffff]
> [ 2.748630] debug: unmapping init [mem 0xffff8800021ad000-0xffff8800021fffff]
> [ 2.752857] ------------[ cut here ]------------
> [ 2.753355] WARNING: CPU: 0 PID: 1 at kernel/res_counter.c:28 res_counter_uncharge_locked+0x48/0x74()
> [ 2.753355] CPU: 0 PID: 1 Comm: init Not tainted 3.16.0-rc1-00238-gddc5bfe #1
> [ 2.753355] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> [ 2.753355] 0000000000000000 ffff880012073c50 ffffffff81a23b9d ffff880012073c88
> [ 2.753355] ffffffff810bc765 ffffffff8111fac8 0000000000001000 ffff88001200fa50
> [ 2.753355] 0000000000000001 ffff88001200fa01 ffff880012073c98 ffffffff810bc84b
> [ 2.753355] Call Trace:
> [ 2.753355] [<ffffffff81a23b9d>] dump_stack+0x19/0x1b
> [ 2.753355] [<ffffffff810bc765>] warn_slowpath_common+0x73/0x8c
> [ 2.753355] [<ffffffff8111fac8>] ? res_counter_uncharge_locked+0x48/0x74
> [ 2.753355] [<ffffffff810bc84b>] warn_slowpath_null+0x1a/0x1c
> [ 2.753355] [<ffffffff8111fac8>] res_counter_uncharge_locked+0x48/0x74
> [ 2.753355] [<ffffffff8111fd02>] res_counter_uncharge_until+0x4e/0xa9
> [ 2.753355] [<ffffffff8111fd70>] res_counter_uncharge+0x13/0x15
> [ 2.753355] [<ffffffff8119499c>] mem_cgroup_uncharge_end+0x73/0x8d
> [ 2.753355] [<ffffffff8115735e>] release_pages+0x1f2/0x20d
> [ 2.753355] [<ffffffff8116cc3a>] tlb_flush_mmu_free+0x28/0x43
> [ 2.753355] [<ffffffff8116d5e5>] tlb_flush_mmu+0x20/0x23
> [ 2.753355] [<ffffffff8116d5fc>] tlb_finish_mmu+0x14/0x39
> [ 2.753355] [<ffffffff811730c1>] unmap_region+0xcd/0xdf
> [ 2.753355] [<ffffffff81172b0e>] ? vma_gap_callbacks_propagate+0x18/0x33
> [ 2.753355] [<ffffffff81174bf1>] do_munmap+0x252/0x2e0
> [ 2.753355] [<ffffffff81174cc3>] vm_munmap+0x44/0x5c
> [ 2.753355] [<ffffffff81174cfe>] SyS_munmap+0x23/0x29
> [ 2.753355] [<ffffffff81a31567>] system_call_fastpath+0x16/0x1b
> [ 2.753355] ---[ end trace cfeb07101f6fbdfb ]---
> [ 2.780913] ------------[ cut here ]------------
This is an underflow that happens with memcg enabled but memcg-swap
disabled - the memsw counter is not accounted, but then unaccounted.
Andrew, can you please put this in to fix the uncharge rewrite patch
mentioned above?
---
>From 29bcfcf54494467008aaf9d4e37771d3b2e2c2c7 Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@...xchg.org>
Date: Fri, 20 Jun 2014 11:09:14 -0400
Subject: [patch] mm: memcontrol: rewrite uncharge API fix
It's not entirely clear whether do_swap_account or PCG_MEMSW is the
authoritative answer to whether a page is swap-accounted or not. This
currently leads to the following memsw counter underflow when swap
accounting is disabled:
[ 2.753355] WARNING: CPU: 0 PID: 1 at kernel/res_counter.c:28 res_counter_uncharge_locked+0x48/0x74()
[ 2.753355] CPU: 0 PID: 1 Comm: init Not tainted 3.16.0-rc1-00238-gddc5bfe #1
[ 2.753355] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 2.753355] 0000000000000000 ffff880012073c50 ffffffff81a23b9d ffff880012073c88
[ 2.753355] ffffffff810bc765 ffffffff8111fac8 0000000000001000 ffff88001200fa50
[ 2.753355] 0000000000000001 ffff88001200fa01 ffff880012073c98 ffffffff810bc84b
[ 2.753355] Call Trace:
[ 2.753355] [<ffffffff81a23b9d>] dump_stack+0x19/0x1b
[ 2.753355] [<ffffffff810bc765>] warn_slowpath_common+0x73/0x8c
[ 2.753355] [<ffffffff8111fac8>] ? res_counter_uncharge_locked+0x48/0x74
[ 2.753355] [<ffffffff810bc84b>] warn_slowpath_null+0x1a/0x1c
[ 2.753355] [<ffffffff8111fac8>] res_counter_uncharge_locked+0x48/0x74
[ 2.753355] [<ffffffff8111fd02>] res_counter_uncharge_until+0x4e/0xa9
[ 2.753355] [<ffffffff8111fd70>] res_counter_uncharge+0x13/0x15
[ 2.753355] [<ffffffff8119499c>] mem_cgroup_uncharge_end+0x73/0x8d
[ 2.753355] [<ffffffff8115735e>] release_pages+0x1f2/0x20d
[ 2.753355] [<ffffffff8116cc3a>] tlb_flush_mmu_free+0x28/0x43
[ 2.753355] [<ffffffff8116d5e5>] tlb_flush_mmu+0x20/0x23
[ 2.753355] [<ffffffff8116d5fc>] tlb_finish_mmu+0x14/0x39
[ 2.753355] [<ffffffff811730c1>] unmap_region+0xcd/0xdf
[ 2.753355] [<ffffffff81172b0e>] ? vma_gap_callbacks_propagate+0x18/0x33
[ 2.753355] [<ffffffff81174bf1>] do_munmap+0x252/0x2e0
[ 2.753355] [<ffffffff81174cc3>] vm_munmap+0x44/0x5c
[ 2.753355] [<ffffffff81174cfe>] SyS_munmap+0x23/0x29
[ 2.753355] [<ffffffff81a31567>] system_call_fastpath+0x16/0x1b
[ 2.753355] ---[ end trace cfeb07101f6fbdfb ]---
Don't set PCG_MEMSW when swap accounting is disabled, so that
uncharging only has to look at this per-page flag.
mem_cgroup_swapout() could also fully rely on this flag, but as it can
bail out before even looking up the page_cgroup, check do_swap_account
as a performance optimization and only sanity test for PCG_MEMSW.
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
mm/memcontrol.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 94d7c40b9f26..d6a20935f9c4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2740,7 +2740,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
* have the page locked
*/
pc->mem_cgroup = memcg;
- pc->flags = PCG_USED | PCG_MEM | PCG_MEMSW;
+ pc->flags = PCG_USED | PCG_MEM | (do_swap_account ? PCG_MEMSW : 0);
if (lrucare) {
if (was_on_lru) {
@@ -6598,7 +6598,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
return;
VM_BUG_ON_PAGE(!(pc->flags & PCG_MEM), oldpage);
- VM_BUG_ON_PAGE(!(pc->flags & PCG_MEMSW), oldpage);
+ VM_BUG_ON_PAGE(do_swap_account && !(pc->flags & PCG_MEMSW), oldpage);
pc->flags &= ~(PCG_MEM | PCG_MEMSW);
if (PageTransHuge(oldpage)) {
--
2.0.0
--
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