On Mon, 25 Mar 2024 08:57:52 +0100 Vlastimil Babka <vbabka@xxxxxxx> wrote:
> On 3/21/24 15:24, Matthew Wilcox (Oracle) wrote:
> > The current folio_test_hugetlb() can be fooled by a concurrent folio split
> > into returning true for a folio which has never belonged to hugetlbfs.
> > This can't happen if the caller holds a refcount on it, but we have a
> > few places (memory-failure, compaction, procfs) which do not and should
> > not take a speculative reference.
>
> In compaction and with CONFIG_DEBUG_VM enabled, the current implementation
> can result in an oops, as reported by Luis. This happens since 9c5ccf2db04b
> ("mm: remove HUGETLB_PAGE_DTOR") effectively added some VM_BUG_ON() checks
> in the PageHuge() testing path.
>
> > Since hugetlb pages do not use individual page mapcounts (they are always
> > fully mapped and use the entire_mapcount field to record the number
> > of mappings), the PageType field is available now that page_mapcount()
> > ignores the value in this field.
>
> Reported-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218227
> Fixes: 9c5ccf2db04b ("mm: remove HUGETLB_PAGE_DTOR")
> Cc: <stable@xxxxxxxxxxxxxxx>
Thanks.
The patch doesn't work as a standalone thing.
In file included from ./include/linux/mmzone.h:23,
from ./include/linux/gfp.h:7,
from ./include/linux/slab.h:16,
from ./include/linux/crypto.h:17,
from arch/x86/kernel/asm-offsets.c:9:
./include/linux/page-flags.h:1021:1: error: return type defaults to 'int' [-Werror=implicit-int]
1021 | FOLIO_TYPE_OPS(hugetlb, hugetlb)
| ^~~~~~~~~~~~~~
./include/linux/page-flags.h:1021:1: error: function declaration isn't a prototype [-Werror=strict-prototypes]
./include/linux/page-flags.h: In function 'FOLIO_TYPE_OPS':
./include/linux/page-flags.h:1035:1: error: expected '=', ',', ';', 'asm' or '__attribute__' before '{' token
<a million more>
Matthew, could you please redo this patch (and its vmcore fix) and send
as a standalone -stable patch? It could be that the "Various
significant MM patches" will need a redo afterwards.
