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