On 8/7/20 9:48 AM, Kirill A. Shutemov wrote:
[...]
+static inline int head_mapcount(struct page *head)
+{
Do we want VM_BUG_ON_PAGE(!PageHead(head), head) here?
Well, no. That was the point of the bug report -- by the time we called
compound_mapcount, the page was no longer a head page.
On Fri, Aug 07, 2020 at 04:10:29PM +0100, Matthew Wilcox wrote:
> On Fri, Aug 07, 2020 at 05:35:04PM +0300, Kirill A. Shutemov wrote:
> > On Tue, Aug 04, 2020 at 02:48:07PM -0700, John Hubbard wrote:
> > > If a compound page is being split while dump_page() is being run on that
> > > page, we can
On Fri, Aug 07, 2020 at 05:35:04PM +0300, Kirill A. Shutemov wrote:
> On Tue, Aug 04, 2020 at 02:48:07PM -0700, John Hubbard wrote:
> > If a compound page is being split while dump_page() is being run on that
> > page, we can end up calling compound_mapcount() on a page that is no
> > longer
On Thu, Aug 06, 2020 at 06:15:00PM +0100, Matthew Wilcox wrote:
> On Thu, Aug 06, 2020 at 05:53:10PM +0200, Vlastimil Babka wrote:
> > On 8/6/20 5:39 PM, Matthew Wilcox wrote:
> > >> >> +++ b/mm/huge_memory.c
> > >> >> @@ -2125,7 +2125,7 @@ static void __split_huge_pmd_locked(struct
> > >> >>
On Tue, Aug 04, 2020 at 02:48:07PM -0700, John Hubbard wrote:
> If a compound page is being split while dump_page() is being run on that
> page, we can end up calling compound_mapcount() on a page that is no
> longer compound. This leads to a crash (already seen at least once in
> the field), due
On Thu, Aug 06, 2020 at 01:45:11PM +0200, Vlastimil Babka wrote:
> How about this additional patch now that we have head_mapcoun()? (I wouldn't
> go for squashing as the goal and scope is too different).
I like it. It bothers me that the compiler doesn't know that
compound_head(compound_head(x))
On Thu, Aug 06, 2020 at 05:53:10PM +0200, Vlastimil Babka wrote:
> On 8/6/20 5:39 PM, Matthew Wilcox wrote:
> >> >> +++ b/mm/huge_memory.c
> >> >> @@ -2125,7 +2125,7 @@ static void __split_huge_pmd_locked(struct
> >> >> vm_area_struct *vma, pmd_t *pmd,
> >> >> * Set PG_double_map before
On 8/4/20 11:48 PM, John Hubbard wrote:
> If a compound page is being split while dump_page() is being run on that
> page, we can end up calling compound_mapcount() on a page that is no
> longer compound. This leads to a crash (already seen at least once in
> the field), due to the
On Thu, Aug 06, 2020 at 05:13:05PM +0200, Vlastimil Babka wrote:
> On 8/6/20 3:48 PM, Matthew Wilcox wrote:
> > On Thu, Aug 06, 2020 at 01:45:11PM +0200, Vlastimil Babka wrote:
> >> How about this additional patch now that we have head_mapcoun()? (I
> >> wouldn't
> >> go for squashing as the goal
On 8/6/20 3:48 PM, Matthew Wilcox wrote:
> On Thu, Aug 06, 2020 at 01:45:11PM +0200, Vlastimil Babka wrote:
>> How about this additional patch now that we have head_mapcoun()? (I wouldn't
>> go for squashing as the goal and scope is too different).
>
> I like it. It bothers me that the compiler
On 8/6/20 5:39 PM, Matthew Wilcox wrote:
>> >> +++ b/mm/huge_memory.c
>> >> @@ -2125,7 +2125,7 @@ static void __split_huge_pmd_locked(struct
>> >> vm_area_struct *vma, pmd_t *pmd,
>> >>* Set PG_double_map before dropping compound_mapcount to avoid
>> >>* false-negative page_mapped().
>>
If a compound page is being split while dump_page() is being run on that
page, we can end up calling compound_mapcount() on a page that is no
longer compound. This leads to a crash (already seen at least once in
the field), due to the VM_BUG_ON_PAGE() assertion inside
compound_mapcount().
(The
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