On Mon, Aug 26, 2013 at 06:28:33PM -0400, Dave Jones wrote:
> >
> > I've not tried matching up bits with Dave's reports, and just going
> > into a meeting now, but this patch looks worth a try: probably Cyrill
> > can improve it meanwhile to what he actually wants there (I'm
> > surprised anything special is needed for just moving a pte).
> >
> > Hugh
> >
> > --- 3.11-rc7/mm/mremap.c 2013-07-14 17:10:16.640003652 -0700
> > +++ linux/mm/mremap.c 2013-08-26 14:46:14.460027627 -0700
> > @@ -126,7 +126,7 @@ static void move_ptes(struct vm_area_str
> > continue;
> > pte = ptep_get_and_clear(mm, old_addr, old_pte);
> > pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
> > - set_pte_at(mm, new_addr, new_pte, pte_mksoft_dirty(pte));
> > + set_pte_at(mm, new_addr, new_pte, pte);
> > }
>
> I'll give this a shot once I'm done with the bisect.
I managed to trigger the issue as well. The patch below fixes it.
Dave, could you please give it a shot once time permit?
Pavel, I kept 'make it dirty on move' logic, but i'm somehow doubt
in it, won't plain pte copying (as in Hugh's patch) work of us?
---
From: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
Subject: [PATCH] mm: move_ptes -- Set soft dirty bit depending on pte type
Dave reported corrupted swap entries
| [ 4588.541886] swap_free: Unused swap offset entry 00002d15
| [ 4588.541952] BUG: Bad page map in process trinity-kid12 pte:005a2a80 pmd:22c01f067
and Hugh pointed that in move_ptes _PAGE_SOFT_DIRTY bit
set regardless the type of entry pte consists of. The
trick here is that -- when we carry soft dirty status
in swap entries we are to use _PAGE_SWP_SOFT_DIRTY instead,
because this is the only place in pte which can be used
for own needs without intersecting with bits owned by
swap entry type/offset.
Reported-by: Dave Jones <davej@xxxxxxxxxx>
Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Hillf Danton <dhillf@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mremap.c | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
Index: linux-2.6.git/mm/mremap.c
===================================================================
--- linux-2.6.git.orig/mm/mremap.c
+++ linux-2.6.git/mm/mremap.c
@@ -15,6 +15,7 @@
#include <linux/swap.h>
#include <linux/capability.h>
#include <linux/fs.h>
+#include <linux/swapops.h>
#include <linux/highmem.h>
#include <linux/security.h>
#include <linux/syscalls.h>
@@ -69,6 +70,23 @@ static pmd_t *alloc_new_pmd(struct mm_st
return pmd;
}
+static pte_t move_soft_dirty_pte(pte_t pte)
+{
+ /*
+ * Set soft dirty bit so we can notice
+ * in userspace the ptes were moved.
+ */
+#ifdef CONFIG_MEM_SOFT_DIRTY
+ if (pte_present(pte))
+ pte = pte_mksoft_dirty(pte);
+ else if (is_swap_pte(pte))
+ pte = pte_swp_mksoft_dirty(pte);
+ else if (pte_file(pte))
+ pte = pte_file_mksoft_dirty(pte);
+#endif
+ return pte;
+}
+
static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
unsigned long old_addr, unsigned long old_end,
struct vm_area_struct *new_vma, pmd_t *new_pmd,
@@ -126,7 +144,8 @@ static void move_ptes(struct vm_area_str
continue;
pte = ptep_get_and_clear(mm, old_addr, old_pte);
pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
- set_pte_at(mm, new_addr, new_pte, pte_mksoft_dirty(pte));
+ pte = move_soft_dirty_pte(pte);
+ set_pte_at(mm, new_addr, new_pte, pte);
}
arch_leave_lazy_mmu_mode();
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