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

[Felipe Balbi]

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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