Re: [PATCH] cgroup/kmemleak: add kmemleak_free() for cgroup deallocations.

[Michal Hocko]

On Thu 18-09-14 09:38:05, Wang Nan wrote:
> Commit ff7ee93f4 introduces kmemleak_alloc() for alloc_page_cgroup(),
> but corresponding kmemleak_free() is missing, which makes kmemleak be
> wrongly disabled after memory offlining. Log is pasted at the end of
> this commit message.
> 
> This patch add kmemleak_free() into free_page_cgroup(). During page
> offlining, this patch removes corresponding entries in kmemleak rbtree.
> After that, the freed memory can be allocated again by other subsystems
> without killing kmemleak.
> 
> bash # for x in 1 2 3 4; do echo offline > /sys/devices/system/memory/memory$x/state ; sleep 1; done ; dmesg | grep leak
> [   45.537934] Offlined Pages 32768
> [   46.617892] kmemleak: Cannot insert 0xffff880016969000 into the object search tree (overlaps existing)
> [   46.617892] CPU: 0 PID: 412 Comm: sleep Not tainted 3.17.0-rc5+ #86
> [   46.617892] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> [   46.617892]  ffff880016823d10 ffff880018bdfc38 ffffffff81725d2c ffff88001780e950
> [   46.617892]  ffff880016969000 ffff880018bdfc88 ffffffff8117a9e6 ffff880018bdfc78
> [   46.617892]  0000000000000096 ffff880017812800 ffffffff81c2eda0 ffff880016969000
> [   46.617892] Call Trace:
> [   46.617892]  [<ffffffff81725d2c>] dump_stack+0x46/0x58
> [   46.617892]  [<ffffffff8117a9e6>] create_object+0x266/0x2c0
> [   46.617892]  [<ffffffff8171d2f6>] kmemleak_alloc+0x26/0x50
> [   46.617892]  [<ffffffff8116a3a3>] kmem_cache_alloc+0xd3/0x160
> [   46.617892]  [<ffffffff81058e59>] __sigqueue_alloc+0x49/0xd0
> [   46.617892]  [<ffffffff8105a41b>] __send_signal+0xcb/0x410
> [   46.617892]  [<ffffffff8105a7a5>] send_signal+0x45/0x90
> [   46.617892]  [<ffffffff8105a803>] __group_send_sig_info+0x13/0x20
> [   46.617892]  [<ffffffff8105bd0b>] do_notify_parent+0x1bb/0x260
> [   46.617892]  [<ffffffff81077e7a>] ? sched_move_task+0xaa/0x130
> [   46.617892]  [<ffffffff81050917>] do_exit+0x767/0xa40
> [   46.617892]  [<ffffffff81050c84>] do_group_exit+0x44/0xa0
> [   46.617892]  [<ffffffff81050cf7>] SyS_exit_group+0x17/0x20
> [   46.617892]  [<ffffffff8172cd12>] system_call_fastpath+0x16/0x1b
> [   46.617892] kmemleak: Kernel memory leak detector disabled
> [   46.617892] kmemleak: Object 0xffff880016900000 (size 524288):
> [   46.617892] kmemleak:   comm "swapper/0", pid 0, jiffies 4294667296
> [   46.617892] kmemleak:   min_count = 0
> [   46.617892] kmemleak:   count = 0
> [   46.617892] kmemleak:   flags = 0x1
> [   46.617892] kmemleak:   checksum = 0
> [   46.617892] kmemleak:   backtrace:
> [   46.617892]      [<ffffffff81d0a7f0>] log_early+0x63/0x77
> [   46.617892]      [<ffffffff8171d31b>] kmemleak_alloc+0x4b/0x50
> [   46.617892]      [<ffffffff81720e4f>] init_section_page_cgroup+0x7f/0xf5
> [   46.617892]      [<ffffffff81d0a6f0>] page_cgroup_init+0xc5/0xd0
> [   46.617892]      [<ffffffff81ce4ed9>] start_kernel+0x333/0x408
> [   46.617892]      [<ffffffff81ce45b2>] x86_64_start_reservations+0x2a/0x2c
> [   46.617892]      [<ffffffff81ce46a9>] x86_64_start_kernel+0xf5/0xfc
> [   46.617892]      [<ffffffffffffffff>] 0xffffffffffffffff
> 
> Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxx>

And sorry, I should have noticed that when reviewing the original patch
which added kmemleak_alloc.

I think this is worth going into stable. The risk is marginal and
somebody might be relying on kmemleak even on older kernels when
debugging a bug during memory hotplug.

Thanks!

> ---
>  mm/page_cgroup.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
> index 3708264..5331c2b 100644
> --- a/mm/page_cgroup.c
> +++ b/mm/page_cgroup.c
> @@ -171,6 +171,7 @@ static void free_page_cgroup(void *addr)
>  			sizeof(struct page_cgroup) * PAGES_PER_SECTION;
>  
>  		BUG_ON(PageReserved(page));
> +		kmemleak_free(addr);
>  		free_pages_exact(addr, table_size);
>  	}
>  }
> -- 
> 1.8.4
> 

-- 
Michal Hocko
SUSE Labs
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