Re: [PATCH] mm/hugetlb: Use compound page head in migrate_huge_page

[Michal Hocko]

On Mon 28-05-12 20:51:30, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> 
> The change was introduced by "hugetlb: simplify migrate_huge_page() "
> 
> We should use compound page head instead of tail pages in
> migrate_huge_page().
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> ---
>  mm/memory-failure.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> This is an important bug fix. If we want we can fold it with the not
> yet merged upstream patch mentioned above in linux-next. The stack
> trace for the crash is
> 
> [   75.337421] BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
> [   75.338386] IP: [<ffffffff816b3f0f>] __mutex_lock_common+0xa1/0x350
> [   75.338386] PGD 1d700067 PUD 1d7dd067 PMD 0
> [   75.338386] Oops: 0002 [#1] SMP
> [   75.338386] CPU 1
> [   75.338386] Modules linked in:
> ...
> ...
> 
> [   75.338386] Call Trace:
> [   75.338386]  [<ffffffff810ffc04>] ? try_to_unmap_file+0x38/0x51c
> [   75.338386]  [<ffffffff810ffc04>] ? try_to_unmap_file+0x38/0x51c
> [   75.338386]  [<ffffffff813b5f8b>] ? vsnprintf+0x83/0x421
> [   75.338386]  [<ffffffff816b427d>] mutex_lock_nested+0x2a/0x31
> [   75.338386]  [<ffffffff8110999b>] ? alloc_huge_page_node+0x1d/0x55
> [   75.338386]  [<ffffffff810ffc04>] try_to_unmap_file+0x38/0x51c
> [   75.338386]  [<ffffffff8110999b>] ? alloc_huge_page_node+0x1d/0x55
> [   75.338386]  [<ffffffff810a06b9>] ? arch_local_irq_save+0x9/0xc
> [   75.338386]  [<ffffffff816b5e3b>] ? _raw_spin_unlock+0x23/0x27
> [   75.338386]  [<ffffffff81100839>] try_to_unmap+0x25/0x3c
> [   75.338386]  [<ffffffff810641c2>] ? console_unlock+0x210/0x238
> [   75.338386]  [<ffffffff811141e3>] migrate_huge_page+0x8d/0x178

This should be part of the changelog.

> 
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 4a45098..53a1495 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1428,8 +1428,8 @@ static int soft_offline_huge_page(struct page *page, int flags)
>  	}
>  
>  	/* Keep page count to indicate a given hugepage is isolated. */
> -	ret = migrate_huge_page(page, new_page, MPOL_MF_MOVE_ALL, 0, true);
> -	put_page(page);
> +	ret = migrate_huge_page(hpage, new_page, MPOL_MF_MOVE_ALL, 0, true);
> +	put_page(hpage);
>  	if (ret) {
>  		pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
>  			pfn, ret, page->flags);

I guess you want hpage->flags here.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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