Re: [memcontrol] WARNING: CPU: 0 PID: 1 at kernel/res_counter.c:28 res_counter_uncharge_locked()

[Johannes Weiner]

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?

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