Hi Naoya,
On Thu, Aug 22, 2013 at 11:51:32AM -0400, Naoya Horiguchi wrote:
>Hi Wanpeng,
>
>On Thu, Aug 22, 2013 at 05:48:22PM +0800, Wanpeng Li wrote:
>> memory_failure() store the page flag of the error page before doing unmap,
>> and (only) if the first check with page flags at the time decided the error
>> page is unknown, it do the second check with the stored page flag since
>> memory_failure() does unmapping of the error pages before doing page_action().
>> This unmapping changes the page state, especially page_remove_rmap() (called
>> from try_to_unmap_one()) clears PG_mlocked, so page_action() can't catch
>> mlocked pages after that.
>>
>> However, memory_failure() can't handle memory errors on dirty mlocked pages
>> correctly. try_to_unmap_one will move the dirty bit from pte to the physical
>> page, the second check lose it since it check the stored page flag. This patch
>> fix it by restore PG_dirty flag to stored page flag if the page is dirty.
>
>Right. And I'm guessing that the discrepancy between pte_dirty and PageDirty
>can happen on the situations rather than mlocked pages.
>Anyway, using both of page flags before and after unmapping looks right to me.
>
The first check is p->flags which will contain PG_dirty flags if pte_dirty
is set. The second check which introduced by commit 524fca1e(HWPOISON:
fix misjudgement of page_action() for errors on mlocked pages) is just
for mlock page case.
>Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
>
Thanks for your review and quick feedback. ;-)
Regards,
Wanpeng Li
>
>> Testcase:
>>
>> #define _GNU_SOURCE
>> #include <stdlib.h>
>> #include <stdio.h>
>> #include <sys/mman.h>
>> #include <sys/types.h>
>> #include <errno.h>
>>
>> #define PAGES_TO_TEST 2
>> #define PAGE_SIZE 4096
>>
>> int main(void)
>> {
>> char *mem;
>> int i;
>>
>> mem = mmap(NULL, PAGES_TO_TEST * PAGE_SIZE,
>> PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_LOCKED, 0, 0);
>>
>> for (i = 0; i < PAGES_TO_TEST; i++)
>> mem[i * PAGE_SIZE] = 'a';
>>
>> if (madvise(mem, PAGES_TO_TEST * PAGE_SIZE, MADV_HWPOISON) == -1)
>> return -1;
>>
>> return 0;
>> }
>>
>> Before patch:
>>
>> [ 912.839247] Injecting memory failure for page 7dfb8 at 7f6b4e37b000
>> [ 912.839257] MCE 0x7dfb8: clean mlocked LRU page recovery: Recovered
>> [ 912.845550] MCE 0x7dfb8: clean mlocked LRU page still referenced by 1 users
>> [ 912.852586] Injecting memory failure for page 7e6aa at 7f6b4e37c000
>> [ 912.852594] MCE 0x7e6aa: clean mlocked LRU page recovery: Recovered
>> [ 912.858936] MCE 0x7e6aa: clean mlocked LRU page still referenced by 1 users
>>
>> After patch:
>>
>> [ 163.590225] Injecting memory failure for page 91bc2f at 7f9f5b0e5000
>> [ 163.590264] MCE 0x91bc2f: dirty mlocked LRU page recovery: Recovered
>> [ 163.596680] MCE 0x91bc2f: dirty mlocked LRU page still referenced by 1 users
>> [ 163.603831] Injecting memory failure for page 91cdd3 at 7f9f5b0e6000
>> [ 163.603852] MCE 0x91cdd3: dirty mlocked LRU page recovery: Recovered
>> [ 163.610305] MCE 0x91cdd3: dirty mlocked LRU page still referenced by 1 users
>>
>> Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
>> ---
>> mm/memory-failure.c | 3 +++
>> 1 files changed, 3 insertions(+), 0 deletions(-)
>>
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index bee58d8..e156084 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -1206,6 +1206,9 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
>> for (ps = error_states;; ps++)
>> if ((p->flags & ps->mask) == ps->res)
>> break;
>> +
>> + page_flags |= (p->flags & (1UL << PG_dirty));
>> +
>> if (!ps->mask)
>> for (ps = error_states;; ps++)
>> if ((page_flags & ps->mask) == ps->res)
>> --
>> 1.7.7.6
>>
>
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