Re: [PATCH 1/3] Unlock the locked hugetlb page withoutMF_COUNT_INCREASED.

From: Naoya Horiguchi
Date: Fri Jan 21 2011 - 00:15:56 EST


On Fri, Jan 21, 2011 at 10:23:26AM +0900, Jin Dongming wrote:
> When the unmapped hugetlb page is poisoned, the page is locked
> for checking some conditions of page. When one of the following condition
> in __memory_failure()
> if (!PageHWPoison(hpage)
> || (hwpoison_filter(p) && TestClearPageHWPoison(p))
> || (p != hpage && TestSetPageHWPoison(hpage) {
> ...
> }
>
> is matched, it just returns from __memory_failure() without unlocking
> the locked hugetlb page. This will block the process which wants to
> map the blocked hugetlb page.
>
> If some process is blocked, error message could be outputted as following:
> kernel: INFO: task hmmap:3307 blocked for more than 120 seconds.
> kernel: "echo 0 > /proc/sys/ kernel/hung_task_timeout_secs" disables this message.
> kernel: hmmap D ffff880196946100 0 3307 1 0x00000080
> kernel: ffff880196946100 0000000000000086 ffff880195ca6040 0000000000000000
> kernel: 0000000000000046 ffffffff81036a7d ffffffff81d08980 0000000000000000
> kernel: ffffffff8189c74c ffffffff814f6886 000000000000002e 0000000000000246
> kernel: Call Trace:
> kernel: [<ffffffff81036a7d>] ? release_console_sem+0x174/0x18e
> kernel: [<ffffffff810914f4>] ? sync_page+0x0/0x48
> kernel: [<ffffffff813bcbdb>] ? io_schedule+0x56/0x8c
> kernel: [<ffffffff81091538>] ? sync_page+0x44/0x48
> kernel: [<ffffffff813bd0ab>] ? __wait_on_bit_lock+0x3e/0x83
> kernel: [<ffffffff810914e1>] ? __lock_page+0x5e/0x64
> kernel: [<ffffffff8104ea89>] ? wake_bit_function+0x0/0x23
> kernel: [<ffffffff810bd723>] ? hugetlb_fault+0x38e/0x6ef
> kernel: [<ffffffff813c11ac>] ? do_page_fault+0x283/0x3dd
> kernel: [<ffffffff81032546>] ? __wake_up+0x30/0x44
> kernel: [<ffffffff813be79f>] ? page_fault+0x1f/0x30
>
> This is because the hugetlb page has been locked in __memory_failure(),
> the process will be blocked by lock_page() in hugetlb_fault()
> all the time.
>
> So this patch unlock the locked hugetlb page before returning from
> __memory_failure().
>
> Signed-off-by: Jin Dongming <jin.dongming@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx>
> ---
> mm/memory-failure.c | 1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 548fbd7..8665eed 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1000,6 +1000,7 @@ int __memory_failure(unsigned long pfn, int trapno, int flags)
> || (hwpoison_filter(p) && TestClearPageHWPoison(p))
> || (p != hpage && TestSetPageHWPoison(hpage))) {
> atomic_long_sub(nr_pages, &mce_bad_pages);
> + unlock_page(hpage);

Good fix, thank you.

Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
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