On Fri, Jun 20, 2014 at 11:42:10AM -0400, Johannes Weiner wrote:
> 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@xxxxxxxxxxx>
> > AuthorDate: Fri Jun 20 10:27:58 2014 +1000
> > Commit: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> > 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@xxxxxxxxxxx>
> > Cc: Michal Hocko <mhocko@xxxxxxx>
> > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> > Cc: Tejun Heo <tj@xxxxxxxxxx>
> > Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> >
> > +-----------------------------------------------------------------------+------------+------------+---------------+
> > | | 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@xxxxxxxxxxx>
> 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@xxxxxxxxxxx>
I was having the same issue with today's linux-next and this patch fixes
it. Before looking at the mailing list I had patched it in a different
way (adding '&& do_swap_account' to mem_cgroup_uncharge_end() check).
Not even enabling swap accounting is a much better approach, indeed.
Tested-by: Felipe Balbi <balbi@xxxxxx>
> ---
> 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)) {
--
balbi
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